The present invention relates to a method of improving the melt processing of thermoplastics by forming blends with segmental polymers. The present invention further relates to articles produced thereby.
Compositions of the thermoplastic polymer xe2x80x9cpoly(vinyl chloride)xe2x80x9d, xe2x80x9cPVCxe2x80x9d, in the absence of a plasticizer or processing aid, are difficult to process into homogeneous, useful articles. The compositions are difficult to flux (i.e., to transition from a solids blend to a fused melt blend), and the resulting melts are heterogeneous and xe2x80x9ccheesyxe2x80x9d having poor melt strength and low elongation. Plasticizers eliminate many of these processing problems but with a resultant loss of physical properties, particularly rigidity, in the thermoplastic articles produced.
Processing aids for PVC are polymeric additives that allow PVC to be processed to give good physical properties without loss of rigidity. It is known in the art that reducing the glass transition temperature, Tg, of processing aids for PVC allows those processing aids to disperse more completely into PVC (U.S. Pat. No. 3,833,686, EP394659). This can be seen in improved clarity and reduced gel defects in clear PVC sheet and indirectly in how rapidly the PVC fuses from a solids blend into a thermoplastic melt blend during processing. This greater ease of fusion manifests itself in, for example, shorter fusion time at a given temperature, or the achievement of a given fusion time at a lower temperature.
Unfortunately, there are limits to the extent to which the Tg of a processing aid can be lowered in that the processing aid, in the dry state, must be a free flowing solid, typically a powder, and it must remain so under typical storage conditions in order to be blended and formulated with PVC powder prior to melt processing. If the processing aid is an emulsion or suspension polymer it must not fuse or form a film during its isolation which is typically accomplished by such operations as spray drying at elevated temperature. Typically, if the Tg of the processing aid drops below 50xc2x0 C., a free flowing, storage stable powder can not be obtained, nor can the clumps, or even xe2x80x9cbricksxe2x80x9d that form during storage be easily broken down during solids blending to form a uniform solids blend.
One approach to reducing overall Tg of a processing aid is to use polymers prepared in two polymerization stages, wherein one component has a reduced Tg. U.S. Pat. No. 3,833,686 discloses two-stage sequentially produced, core-shell particles made by emulsion polymerization, wherein the lower Tg component is the core and a high Tg material, e.g., methyl methacrylate (MMA) is the shell. These core-shell particles contain substantially proportions of low Tg polymers having no high Tg segment, high Tg polymers having no low Tg segments, and polymers having both high and low Tg segments. Further, many of the chains are very long and have networked structure due to adventitious crosslinking. While one achieves a free flowing powder in this way even if the Tg of the core is near to, or below, room temperature, it is an unfortunate reality that such polymer particles are unable to break down fully during melt processing and, therefore, cannot realize their full potential as processing aid.
We have, surprisingly, found that segmental copolymers may be produced as non-tacky powders, yet behave as processing aids for thermoplastics (e.g., PVC), providing short fusion times and low fusion temperatures consistent with those promoted by low Tg processing aids. These segmental copolymers can further be stored under typical conditions without compacting, clumping, or fusing. They can be transported to a processing hall, and combined with thermoplastics to make solids blends, again without clumping. Heating and mixing of these solids blends produces melt blends, having improved melt processing behavior, that can be shaped and cooled to produce homogeneous, useful thermoplastic articles. Such improved processing behavior is essential if articles of consistently high quality are to be produced at high output rates with minimal downtime in such processing operations as, for example, calendering, extrusion, blow molding, injection molding, expansion into foam, and making of bi-oriented materials.
One aspect of the present invention relates to a method comprising the steps of:
(a) forming a solids blend comprising a thermoplastic polymer and a segmental copolymer; and
(b) mixing and heating said solids blend to form a melt blend;
wherein said melt blend has a melt processing improvement term having a value of at least 10.
A second aspect of the present invention relates to a method comprising the steps of:
(a) forming a solids blend comprising a thermoplastic polymer and a segmental copolymer;
(b) mixing and heating said solids blend to form a melt blend;
(c) shaping said melt blend to form an article; and
(d) cooling said article to room temperature;
wherein said melt blend has a melt processing improvement term having a value of at least 10.
A third aspect of the present invention relates to an article, wherein said article comprises a thermoplastic polymer and a segmental copolymer.
A fourth aspect of the present invention relates to a plastic article produced by the method of the second aspect of the present invention.
In another aspect, the thermoplastic polymer of aspects one through four is a polymer selected from the group consisting of poly(vinyl halide) homopolymer, poly(vinyl halide) copolymer, chlorinated poly(vinyl chloride) xe2x80x9cCPVCxe2x80x9d, and combinations thereof. A preferred thermoplastic polymer is poly(vinyl chloride). In a still further aspect, the segmental copolymer of aspects one through four is a copolymer selected from the group consisting of comb copolymer, block copolymer, and combinations thereof. It is preferred that the segmental copolymer is a comb copolymer.
Used herein, the following terms have these definitions:
The xe2x80x9cbackbonexe2x80x9d of a polymer chain is a collection of polymerized monomer units attached to one another. The attachment is typically achieved by covalent bonding. xe2x80x9cNon-terminalxe2x80x9d monomer units are directly attached to at least two other monomer units. A xe2x80x9cterminalxe2x80x9d monomer unit resides at the end of the polymer chain and is directly attached to one other monomer unit. For example, the polymerized monomer units of the backbone may be derived from ethylenically unsaturated monomers.
A xe2x80x9clinearxe2x80x9d polymer (homopolymer or copolymer) is a polymer having a backbone that is not branched. As used herein, the term xe2x80x9clinearxe2x80x9d is also meant to include polymers wherein a minor amount of branching has occurred. For example, hydrogen abstraction may lead to branching during free radical polymerizations.
A xe2x80x9cbranchedxe2x80x9d polymer is a polymer having a first xe2x80x9cbackbone segmentxe2x80x9d that has other backbone segments (i.e., xe2x80x9cbranchesxe2x80x9d) chemically attached to it through a xe2x80x9cnon-terminalxe2x80x9d atom of the first backbone segment. Typically, this first backbone segment and all of the branches have the same, or similar, composition.
A xe2x80x9cpendantxe2x80x9d group is a group that is attached to the backbone of a polymer. The term pendant may be used to describe a group that is actually part of a polymerized monomer unit. For example, the hydroxyethyl group of a polymerized unit of 2-hydroxyethyl methacrylate may be referred to as a xe2x80x9cpendant hydroxyethyl groupxe2x80x9d, or as xe2x80x9cpendant hydroxy functionalityxe2x80x9d. It is also common to refer to large groups attached to a polymer backbone as xe2x80x9cpendantxe2x80x9d when those large groups are compositionally distinct from the backbone polymer. These large groups may themselves be polymer chains. For example, when a macromonomer becomes incorporated into a polymer chain by reaction with other monomers, the two carbons of its reactive double bond become part of the backbone, while the polymeric chain originally attached to the double bond of the macromonomer becomes a xe2x80x9cpendant groupxe2x80x9d that may, for example, have a molecular weight of 500 to 100,000. A xe2x80x9cpendantxe2x80x9d group may further be described as xe2x80x9cpendant toxe2x80x9d the backbone.
A xe2x80x9cterminalxe2x80x9d group resides at the end of the polymer chain and is chemically attached to a terminal monomer unit. A terminal group may, for example, have a composition distinct from the composition of the backbone of the polymer. A xe2x80x9cpendantxe2x80x9d group may occur in a xe2x80x9cterminalxe2x80x9d position. As such, a xe2x80x9cterminalxe2x80x9d group is a special case of a xe2x80x9cpendantxe2x80x9d group.
A xe2x80x9cmacromonomerxe2x80x9d is any low molecular weight water-insoluble polymer or copolymer having at least one terminal ethylenically unsaturated group that is capable of being polymerized in a free radical polymerization process. By xe2x80x9cwater-insolublexe2x80x9d it is meant having a water solubility of no greater than 150 millimoles/liter at 25xc2x0 C. to 50xc2x0 C. By xe2x80x9clow molecular weightxe2x80x9d it is meant that the macromonomer has a degree of polymerization preferably from 10 to 1,000, more preferably from 20 to 1,000, and most preferably from 20 to 200. By xe2x80x9cdegree of polymerizationxe2x80x9d it is meant the number of polymerized monomer units present in the macromonomer.
A xe2x80x9cmacromonomerxe2x80x9d is a low molecular weight polymer having at least one functional group at the end of the polymer chain that can further polymerize with others monomers to yield comb copolymers. See e.g., Kawakami in the xe2x80x9cEncyclopedia of Polymer Science and Engineeringxe2x80x9d, Vol. 9, pp. 195-204, John Wiley and Sons, New York, 1987. Typically, the macromonomer polymer chain contains ethylenically unsaturated monomers, as polymerized units. Preferably, the ethylenically unsaturated monomer is selected to impart low or no water solubility to the macromonomer as previously described herein.
The term xe2x80x9cmacromonomer aqueous emulsionxe2x80x9d is used herein to describe an aqueous emulsion containing macromonomer dispersed therein as water insoluble particles.
A xe2x80x9cgraft segmentxe2x80x9d is a polymer chain occupying a pendant position along the polymer backbone. A graft segment may include, as polymerized units, one type of monomer or more than one type of monomer. The composition of a graft segment is different from the composition of the backbone polymer to which it is attached, in contrast to a xe2x80x9cbranch segmentxe2x80x9d of a branched backbone which has a composition which is the same as, or similar to, other portions the branched backbone of which it is a part. A xe2x80x9cterminal graft segmentxe2x80x9d resides at an end of a backbone polymer chain and is chemically attached to that backbone polymer chain. A xe2x80x9cterminal graft segmentxe2x80x9d is a special case of a xe2x80x9cpendant graft segmentxe2x80x9d. The comb copolymer (i.e., graft copolymer) of the present invention includes one or more compositional types of graft segment.
xe2x80x9cGraft copolymersxe2x80x9d are macromolecules formed when polymer or copolymer chains are chemically attached as side chains to a polymeric backbone. Those side chains are the xe2x80x9cgraft segmentsxe2x80x9d described herein above. Because graft copolymers often chemically combine unlike polymeric segments in one macromolecule, these copolymers have unique properties compared to the corresponding random copolymer analogues. These properties include, for example, mechanical film properties resulting from thermodynamically driven microphase separation of the copolymer, and decreased melt viscosities resulting in part from the segmental structure of the graft copolymer, and from separation of a soft (i.e., low Tg) phase. With respect to the latter, reduced melt viscosities can advantageously improve processability of the polymer. See e.g., Hong-Quan Xie and Shi-Biao Zhou, J. Macromol. Sci.-Chem., A27(4), 491-507 (1990); Sebastian Roos, Axel H. E. Mxc3xcller, Marita Kaufmann, Werner Siol and Clenens Auschra, xe2x80x9cApplications of Anionic Polymerization Researchxe2x80x9d, R. P. Quirk, Ed., ACS Symp. Ser. 696, 208 (1998).
The term xe2x80x9ccomb copolymer,xe2x80x9d as used herein, refers to the type of copolymer that is the xe2x80x9cgraft copolymerxe2x80x9d of the present invention, wherein the polymeric backbone of the graft copolymer is linear, or essentially linear, and each side chain (graft segment) of the graft copolymer is formed by a xe2x80x9cmacromonomerxe2x80x9d that is grafted to the polymer backbone. The comb copolymers may, for example, be prepared by the free radical copolymerization of macromonomer with conventional monomer (e.g., second ethylenically unsaturated monomer). It is required that either the backbone, the graft segment, or both backbone and graft segment be miscible in the thermoplastic polymer of the present invention. The solubility parameters of the backbone and the thermoplastic polymer can be estimated and compared to predict miscibility by methods such as that of Van Krevelen, described herein below. Used herein, the terms xe2x80x9cgraft copolymerxe2x80x9d and xe2x80x9ccomb copolymerxe2x80x9d are interchangeable.
A xe2x80x9cblock copolymerxe2x80x9d is a copolymer having a backbone characterized by the presence of two or more xe2x80x9cblocksxe2x80x9d. A xe2x80x9cblockxe2x80x9d is a segment of copolymer backbone having a particular and distinct composition. See e.g., G. Odian xe2x80x9cPrinciples of Polymerizationxe2x80x9d, Third Edn., pp. 142-149, John Wiley and Sons, New York, 1991. For example, a block could be composed entirely of styrene monomer, present as polymerized units. At least two blocks differing in composition must be present in a block copolymer, however, more than one block of a given composition may be present. For example, a poly(styrene)-b-poly(butadiene)-b-poly(styrene) has two poly(styrene) blocks joined by a poly(butadiene) block. Blocks are typically at least 10 monomer units, preferably at least 50 monomer units, and more preferably at least 100 monomer units in length.
A xe2x80x9ccopolymer segmentxe2x80x9d is a segment selected from the group including a xe2x80x9cbackbonexe2x80x9d of a comb copolymer, a xe2x80x9cgraft segmentxe2x80x9d of a comb copolymer, and xe2x80x9cblockxe2x80x9d of a block copolymer. It is required that at least one copolymer segment of the segmental copolymer (i.e., comb copolymer or block copolymer) of the present invention is miscible with the thermoplastic polymer. The solubility parameters a given copolymer segment and the thermoplastic polymer can be estimated and compared to predict miscibility by methods such as that of Van Krevelen described herein below. The comb copolymer of the present invention comprises a first copolymer segment and at least one second copolymer segment. The first copolymer segment is the backbone of the comb copolymer, and the second copolymer segment is the graft segment of the comb copolymer.
A xe2x80x9crandom copolymerxe2x80x9d is a copolymer having monomers, as polymerized units, randomly distributed along its backbone. Used herein, the term xe2x80x9crandomxe2x80x9d has its usual meaning in the art of polymerization. For example, the distribution of monomer units along a polymer chain prepared by emulsion polymerization is dictated not only by the relative amounts of each type of monomer present at any point during the polymerization, but also by such factors as, for example, the tendency of each monomer type to react with itself relative to its tendency to react with each of the other types of monomer present. These reactive tendencies are defined by reactivity ratios which are well know for many monomer combinations. See e.g., G. Odian xe2x80x9cPrinciples of Polymerizationxe2x80x9d, Third Edn., pp. 460-492, John Wiley and Sons, New York, 1991.
A xe2x80x9csegmental copolymerxe2x80x9d is a copolymer selected from the group consisting of xe2x80x9cblock copolymerxe2x80x9d, xe2x80x9ccomb copolymerxe2x80x9d, and combinations thereof.
A xe2x80x9caqueous dispersion of a segmental copolymerxe2x80x9d is a aqueous medium in which are dispersed a plurality of particles of segmental copolymer. Used herein, an xe2x80x9caqueous dispersion of a segmental copolymerxe2x80x9d is an xe2x80x9caqueous copolymer compositionxe2x80x9d.
xe2x80x9cTgxe2x80x9d is the xe2x80x9cglass transition temperaturexe2x80x9d of a polymeric phase. The glass transition temperature of a polymer is the temperature at which a polymer transitions from a rigid, glassy state at temperatures below Tg to a fluid or rubbery state at temperatures above Tg. The Tg of a polymer is typically measured by differential scanning calorimetry (DSC) using the mid-point in the heat flow versus temperature transition as the Tg value. A typical heating rate for the DSC measurement is 20 Centigrade degrees per minute. The Tg of various homopolymers may be found, for example, in Polymer Handbook, edited by J. Brandrup and E. H. Immergut, Interscience Publishers. The Tg of a polymer is estimated by using the Fox equation (T. G. Fox, Bull. Am. Physics Soc., Volume 1, Issue No. 3, page 123 (1956)).
xe2x80x9cEffective Tgxe2x80x9d. When a substance having some degree of solubility in a polymer is imbibed by that polymer, the softening temperature of the polymer decreases. This plasticization of the polymer can be characterized by measuring the xe2x80x9ceffective Tgxe2x80x9d of the polymer, which typically bears an inverse relationship to the amount of solvent or other substance contained in the polymer. The xe2x80x9ceffective Tgxe2x80x9d of a polymer containing a known amount of a substance dissolved within is measured just as described above for xe2x80x9cTgxe2x80x9d. Alternatively, the xe2x80x9ceffective Tgxe2x80x9d may be estimated by using the Fox equation (supra), assuming a value for Tg (e.g., the freezing point) of the solvent or other substance contained in the polymer.
Molecular Weight. Synthetic polymers are almost always a mixture of chains varying in molecular weight, i.e., there is a xe2x80x9cmolecular weight distributionxe2x80x9d, abbreviated xe2x80x9cMWDxe2x80x9d. For a homopolymer, members of the distribution differ in the number of monomer units which they contain. This way of describing a distribution of polymer chains also extends to copolymers. Given that there is a distribution of molecular weights, the most complete characterization of the molecular weight of a given sample is the determination of the entire molecular weight distribution. This characterization is obtained by separating the members of the distribution and then quantitating the amount of each that is present. Once this distribution is in hand, there are several summary statistics, or moments, which can be generated from it to characterize the molecular weight of the polymer.
The two most common moments of the distribution are the xe2x80x9cweight average molecular weightxe2x80x9d, xe2x80x9cMwxe2x80x9d, and the xe2x80x9cnumber average molecular weightxe2x80x9d, xe2x80x9cMnxe2x80x9d. These are defined as follows:             M      w        =                  ∑                              (                                          W                i                            ⁢                              M                i                                      )                    /                      ∑                          W              i                                          =              ∑                              (                                          N                i                            ⁢                              M                i                2                                      )                    /                      ∑                                          N                i                            ⁢                              M                i                                                                    M      n        =                  ∑                              W            i                    /                      ∑                          (                                                W                  i                                /                                  M                  i                                            )                                          =              ∑                              (                                          N                i                            ⁢                              M                i                                      )                    /                      ∑                          N              i                                          
where
Mi=molar mass of ith component of distribution
Wi=weight of ith component of distribution
Ni=number of chains of ith component
and the summations are over all the components in the distribution. Mw and Mn are typically computed from the MWD as measured by Gel Permeation Chromatography (see the Experimental Section).
xe2x80x9cParticle sizexe2x80x9d is the diameter of a particle.
The xe2x80x9caverage particle sizexe2x80x9d determined for a collection of particles (e.g., macromonomer particles, or particles of graft copolymer) the xe2x80x9cweight average particle sizexe2x80x9d, xe2x80x9cdwxe2x80x9d, as measured by Capillary Hydrodynamic Fractionation technique using a Matec CHDF 2000 particle size analyzer equipped with a HPLC type Ultra-violet detector.
The term xe2x80x9cparticle size distributionxe2x80x9d and the acronym xe2x80x9cPSDxe2x80x9d are used interchangeably. xe2x80x9cPolydispersityxe2x80x9d is used in the art as a measure of the breadth of the PSD. Used herein, xe2x80x9cpolydispersityxe2x80x9d is a description of the distribution of particle sizes for a plurality of particles. As such, xe2x80x9cpolydispersityxe2x80x9d and xe2x80x9cPSD polydispersityxe2x80x9d are used interchangeably. PSD polydispersity is calculated from the weight average particle size, dw, and the number average particle size, dn, according to the formulae:                     PSD        ⁢                  xe2x80x83                ⁢        Polydispersity            =                        (                      d            w                    )                /                  (                      d            n                    )                      ,    where                                            d            n                    =                    ⁢                      ∑                                          n                i                            ⁢                                                d                  i                                /                                  ∑                                      n                    i                                                                                                                                                              d                w                            =                            ⁢                              ∑                                                      n                    i                                    ⁢                                      d                    i                                    ⁢                                                            d                      i                                        /                                          ∑                                                                        n                          i                                                ⁢                                                  d                          i                                                                                                                                          ,                          and              ⁢                              xe2x80x83                            ⁢              where              ⁢                              xe2x80x83                            ⁢                              n                i                            ⁢                              xe2x80x83                            ⁢              is              ⁢                              xe2x80x83                            ⁢              the              ⁢                              xe2x80x83                            ⁢              number              ⁢                              xe2x80x83                            ⁢              of              ⁢                              xe2x80x83                            ⁢              particles                                ⁢                      "IndentingNewLine"                    ⁢                      having            ⁢                          xe2x80x83                        ⁢            the            ⁢                          xe2x80x83                        ⁢            particle            ⁢                          xe2x80x83                        ⁢            size            ⁢                          xe2x80x83                        ⁢                                          d                i                            .                                          
Estimation of whether a polymer and another component (i.e., another polymer or a solvent) will be miscible may be made according to the well-known methods delineated in D. W. Van Krevelen, Properties of Polymers, 3rd Edition, Elsevier, pp. 189-225, 1990. For example, Van Krevelen defines the total solubility parameter (xcex4t) for a substance by:
xcex4t2=xcex4d2+xcex4p2+xcex4h2,
where xcex4d, xcex4p, and xcex4h are the dispersive, polar, and hydrogen bonding components of the solubility parameter, respectively. Values for xcex4d, xcex4p, and xcex4h have been determined for many solvents, polymers, and polymer segments, and can be estimated using the group contribution methods of Van Krevelen. For example, to estimate whether a polymer having a given composition will be miscible with a particular solvent, one calculates xcex4t2 for the polymer and xcex4t2 for the solvent. Typically, if the difference between the two, xcex94xcex4t2, is greater than 25 (i.e., xcex94xcex4t greater than 5), then the polymer and the solvent will not be miscible.
If, instead, it is desired to determine whether two polymers, differing in composition, will be miscible, the same calculations may be carried out, but the predicted upper limit of xcex94xcex4t2 for miscibility will decrease as the molecular weight of one or both of polymers under consideration increases. This decrease is thought to parallel the decrease in entropy of mixing which occurs as the molecular weight of the components being mixed increases. For example, two polymers, each having a degree of polymerization of 100, will likely be immiscible even if the value of xcex94xcex4t2 for their mixture is 9, or even 4 (i.e., xcex94xcex4t=3, or even 2). Still higher molecular weight polymers may be immiscible at even lower values of xcex94xcex4t. To estimate whether a graft segment of the copolymer of the present invention, having a given composition, will be miscible with a backbone having another composition, one calculates xcex4t2 for the graft segment and xcex4t2 for the backbone. Typically, if the difference between the two, xcex94xcex4t2, is greater than 9 (i.e., xcex94xcex4t greater than 3), then the graft segment should be insoluble in the backbone polymer such that a film formed by the graft copolymer would have two distinct types of polymeric phase. Similar calculation can be performed to determine whether a film formed from a block copolymer will have more than one polymeric phase. Because it is desirable that the graft segment not be miscible with the backbone, the Van Krevelen calculations of miscibility provide useful estimates of whether a given pair of compositions of the graft segment and backbone will result in phase separation in, for example, films formed from the segmental copolymer.
A xe2x80x9cpolymeric additivexe2x80x9d, xe2x80x9cPAxe2x80x9d is a polymer that is added to the thermoplastic polymer composition.
A xe2x80x9cprocessing aidxe2x80x9d is a polymeric additive having a value of IMPxe2x89xa710 (defined below).
A xe2x80x9csolids blendxe2x80x9d is any thermoplastic polymer composition that is substantially solid, and not a melt blend. Such solids blends include, for example, blends of thermoplastic polymer in powder or pellet form with other components that themselves may, or may not, be solids. Through heating and mixing, a solids blend may be transformed into a melt blend.
A xe2x80x9cmelt blendxe2x80x9d is any thermoplastic polymer composition that is substantially in melt form. Fusion of a solids blend, through heating and mixing, creates a melt blend.
xe2x80x9cFusion timexe2x80x9d is the time interval between the initial loading (i.e., compaction) of the test sample in a melt flow instrument (e.g., Haake Rheocord 90 with a Haake Bowl attachment using counter rotating paddles) and the torque maximum which occurs on fusion.
xe2x80x9cFusion temperaturexe2x80x9d is the temperature at which the solids blend becomes a melt blend, and is measured at the point at which the torque reaches its peak (i.e., maximum) value. Fusion temperature depends upon the settings chosen for the melt flow instrument as well as the characteristics of the solids blend.
xe2x80x9cEquilibrium Torquexe2x80x9d is the torque value measured once the torque has become constant after peak torque (at fusion) has occurred.
xe2x80x9cMelt strengthxe2x80x9d is proportional to the torque of a given melt blend. High melt strength is associated with formation of uniform thermoplastic melt blends, consistent processing, and formation of uniform thermoplastic articles.
Because performance properties such as fusion time, fusion temperature, and equilibrium torque are all indicative of the processing performance of a melt of a thermoplastic polymer, consideration of only one of these properties to the exclusion of the others may give an incomplete assessment of the extent to which a given polymeric additive imparts improved melt processing behavior to a thermoplastic polymer. In recognition of that problem, three dimensionless terms are herein defined that express the extent to which each of those three performance properties are improved by the addition of a particular polymeric additive (xe2x80x9cPAxe2x80x9d) to a blend containing a thermoplastic polymer. The fusion time, fusion temperature, and equilibrium torque are measured under a well controlled set of processing conditions (e.g., type of melt blending apparatus, initial temperature, and RPM of mixing element) for a given thermoplastic polymer absent a particular polymeric additive, and then in the presence of that additive at a given level. The three dimensionless terms are then combined (i.e., summed) to give an overall term that more fully describes whether an improvement in melt processing performance has resulted from the presence of the polymeric additive and, if so, the extent of that improvement. All four of these xe2x80x9cimprovement termsxe2x80x9d are defined herein below:
The xe2x80x9cfusion time improvement termxe2x80x9d, xe2x80x9cIFTIxe2x80x9d is defined as:
IFTI=[((FTI without PA)xe2x88x92(FTI with PA))/(FTI without PA)]xc3x97100,
where xe2x80x9cFTIxe2x80x9d is the xe2x80x9cfusion timexe2x80x9d (e.g., in seconds) and xe2x80x9cPAxe2x80x9d is the xe2x80x9cpolymeric additivexe2x80x9d being assessed. If, for example, a PVC masterbatch (see Table 6 below) had a fusion time of 150 seconds, whereas a blend of that PVC masterbatch with a polymeric additive displayed a fusion time of only 75 seconds, the fusion time improvement term would have a value of xe2x80x9c50xe2x80x9d. A positive value of IFTI indicates a shorter fusion time in the presence of the polymeric additive, and shorter fusion times are associated with improved melt processing. Hence, a positive value of IFTI is one indicator that the melt processing of a thermoplastic polymer improves when the polymeric additive being assessed is present.
The xe2x80x9cfusion temperature improvement termxe2x80x9d, xe2x80x9cIFTPxe2x80x9d is defined as:
IFTP=[((FTP without PA)xe2x88x92(FTP with PA))/(FTP without PA)]xc3x97100,
where xe2x80x9cFTPxe2x80x9d is the xe2x80x9cfusion temperaturexe2x80x9d (in xc2x0 C.) and xe2x80x9cPAxe2x80x9d is the xe2x80x9cpolymeric additivexe2x80x9d. As with IFTI, a positive value of IFTP is an indicator that the melt processing of a thermoplastic polymer improves when a the polymeric additive being assessed is present.
The xe2x80x9cequilibrium torque improvement termxe2x80x9d, xe2x80x9cIETxe2x80x9d is defined as:
IET=[((ET with PA)/(ET without PA))xe2x88x921]xc3x97100,
where xe2x80x9cETxe2x80x9d is the xe2x80x9cequilibrium torquexe2x80x9d (e.g., in meter-grams) and xe2x80x9cPAxe2x80x9d is the xe2x80x9cpolymeric additivexe2x80x9d being assessed. If, for example, a PVC masterbatch had an equilibrium torque of 750 mg, whereas a blend of that PVC masterbatch with a polymeric additive displayed a value of 825 mg under identical conditions, the equilibrium torque improvement term would have a value of xe2x80x9c10xe2x80x9d. As with IFTI and IFTP, a positive value of IET is an indicator that the melt processing of a thermoplastic polymer improves when a the polymeric additive being assessed is present. Equilibrium torque correlates directly with melt viscosity which, in turn, is directly correlated with melt strength. Therefore, an increase in equilibrium torque upon addition of polymeric additive indicated increased melt strength, a processing characteristic desired in a thermoplastic melt.
The xe2x80x9cmelt processing improvement termxe2x80x9d, xe2x80x9cIMPxe2x80x9d, more fully describes the ability of a given polymeric additive to improve the melt processing of a thermoplastic polymer through a summation of the other three improvement terms as follows:
IMP=IFTI+IFTP+IET.
The segmental copolymers of the present invention are typically included in melt blends with the thermoplastic polymer at concentrations of 0.5 to 10 PHR (parts per hundred parts, weight/weight), based on the weight of the thermoplastic polymer. Over that concentration range, the segmental copolymers of the present invention preferably have values for the melt processing improvement term, IMP, of greater than 10, more preferably 20 to 200, and most preferably 35 to 200. All ranges used herein are inclusive and combinable.
A preferred method of preparing the graft copolymers of the present invention and their aqueous dispersions is by emulsion polymerization. A preferred process for this preparation includes (a) forming, by polymerization of at least one first ethylenically unsaturated monomer, a macromonomer aqueous emulsion containing one or more water-insoluble particles of macromonomer; (b) forming a monomer composition containing at least one second ethylenically unsaturated monomer; and (c) combining at least a portion of the macromonomer aqueous emulsion and at least a portion of the monomer composition to form a xe2x80x9cpolymerization reaction mixturexe2x80x9d. The macromonomer and second ethylenically unsaturated monomer are polymerized in the presence of an initiator to form graft copolymer particles. The graft copolymers prepared by this preferred process are comb copolymers.
The macromonomer, present in the macromonomer aqueous emulsion as water insoluble particles, is any low molecular weight water-insoluble polymer or copolymer having at least one terminal ethylenically unsaturated group that is capable of being polymerized in a free radical polymerization process. By xe2x80x9cwater-insolublexe2x80x9d it is meant having a water solubility of no greater than 150 millimoles/liter at 25xc2x0 C. to 50xc2x0 C. By xe2x80x9clow molecular weightxe2x80x9d it is meant that the macromonomer has a degree of polymerization of preferably from 10 to 1,000, more preferably from 20 to 1,000, and most preferably from 20 to 200. By xe2x80x9cdegree of polymerizationxe2x80x9d it is meant the number of polymerized monomer units present in the macromonomer.
The macromonomer contains, as polymerized units, at least first ethylenically unsaturated monomer. Preferably, the first ethylenically unsaturated monomer is selected to impart low or no water solubility to the macromonomer as previously described herein.
If the macromonomer will be used to prepare the graft segment of a comb copolymer, the backbone of which is not miscible with the thermoplastic polymer of the present invention, it is required that the composition of the macromonomer be chosen such that the graft segments of the comb copolymer formed therefrom will be miscible in the thermoplastic polymer. If the backbone is miscible with the thermoplastic polymer, the graft segment may, optionally, be miscible in the thermoplastic polymer. The solubility parameters of the macromonomer (and graft segment prepared therefrom) and the thermoplastic polymer can be estimated and compared to predict miscibility by methods such as that of Van Krevelen, described herein above.
The composition of the macromonomer should be chosen so that the Tg of the graft segment of the comb copolymer formed therefrom will be preferably from xe2x88x9265xc2x0 C. to 180xc2x0 C., more preferably from xe2x88x9245xc2x0 C. to 180xc2x0 C., and most preferably from xe2x88x9220xc2x0 C. to 130xc2x0 C.
Suitable first ethylenically unsaturated monomers for use in preparing macromonomer include for example methacrylate esters, such as C1 to C18 normal or branched alkyl esters of methacrylic acid, including methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, lauryl methacrylate, stearyl methacrylate; acrylate esters, such as C1 to C18 normal or branched alkyl esters of acrylic acid, including methyl acrylate, ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate; styrene; substituted styrenes, such as methyl styrene, a-methyl styrene or t-butyl styrene; olefinically unsaturated nitriles, such as acrylonitrile or methacrylonitrile; olefinically unsaturated halides, such as vinyl chloride, vinylidene chloride or vinyl fluoride; vinyl esters of organic acids, such as vinyl acetate; N-vinyl compounds such as N-vinyl pyrrolidone; acrylamide; methacrylamide; substituted acrylamides; substituted methacrylamides; hydroxyalkylmethacrylates such as hydroxyethylmethacrylate; hydroxyalkylacrylates; basic substituted (meth)acrylates and (meth)acrylamides, such as amine-substituted methacrylates including dimethylaminoethyl methacrylate, tertiary-butylaminoethyl methacrylate and dimethylaminopropyl methacrylamide and the likes; dienes such as 1,3-butadiene and isoprene; vinyl ethers; or combinations thereof. The term xe2x80x9c(meth)xe2x80x9d as used herein means that the xe2x80x9cmethxe2x80x9d is optionally present. For example, xe2x80x9c(meth)acrylatexe2x80x9d means methacrylate or acrylate.
The first ethylenically unsaturated monomer can also be a functional monomer including for example monomers containing hydroxy, amido, aldehyde, ureido, polyether, glycidylalkyl, keto functional groups or combinations thereof. These functional monomers are generally present in the macromonomer at a level of from 0.1 weight percent to 15 weight percent and more preferably from 0.5 weight percent to 10 weight percent, and most preferably from 1.0 to 3 weight percent, based on the total weight of the graft copolymer. Used herein, all ranges are inclusive and combinable. Examples of functional monomers include ketofunctional monomers such as the acetoacetoxy esters of hydroxyalkyl acrylates and methacrylates (e.g., acetoacetoxyethyl methacrylate) and keto-containing amides (e.g., diacetone acrylamide); allyl alkyl methacrylates or acrylates; glycidylalkyl methacrylates or acrylates; or combinations thereof. Such functional monomers can provide crosslinking if desired.
The macromonomer typically also contains as polymerized units less than 10 weight percent, preferably less than 5 weight percent, more preferably less than 2 weight percent and most preferably less than 1 weight percent acid containing monomer, based on the total weight of the macromonomer. In a most preferred embodiment, the macromonomer contains no acid containing monomer. Used herein, xe2x80x9cacid containing monomerxe2x80x9d and xe2x80x9cacid functional monomerxe2x80x9d are used interchangeably. By xe2x80x9cacid containing monomerxe2x80x9d it is meant any ethylenically unsaturated monomer that contains one or more acid functional groups or functional groups that are capable of forming an acid (e.g., an anhydride such as methacrylic anhydride or tertiary butyl methacrylate). Examples of acid containing monomers include, for example, carboxylic acid bearing ethylenically unsaturated monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid and fumaric acid; acryloxypropionic acid and (meth)acryloxypropionic acid; sulphonic acid-bearing monomers, such as styrene sulfonic acid, sodium vinyl sulfonate, sulfoethyl acrylate, sulfoethyl methacrylate, ethylmethacrylate-2-sulphonic acid, or 2-acrylamido-2-methylpropane sulphonic acid; phosphoethylmethacrylate; the corresponding salts of the acid containing monomer; or combinations thereof.
The macromonomer may also contains as polymerized units, mercapto-olefins. Used herein, xe2x80x9cmercapto-olefinxe2x80x9d and xe2x80x9cmercaptan-olefinxe2x80x9d are used interchangeably. These mercapto-olefin compounds are those as disclosed in U.S. Pat. No. 5,247,000 to Amick. Further, the methods of U.S. Pat. No. 5,247,000 may be utilized to prepare comb copolymers of the present invention.
In a preferred embodiment of the present invention, the macromonomer is composed of 20 weight percent to 100 weight percent, more preferably from 50 to 100 weight percent, and most preferably from 70 to 100 weight percent, based on total weight of macromonomer, of at least one xcex1-methyl vinyl monomer, a non xcex1-methyl vinyl monomer terminated with an xcex1-methyl vinyl monomer, or combinations thereof. In a most preferred embodiment of the present invention the macromonomer contains as polymerized units from 90 to 100 weight percent xcex1-methyl vinyl monomers, non xcex1-methyl vinyl monomers terminated with xcex1-methyl vinyl monomers, or combinations thereof, based on the total weight of the macromonomer. The phrase xe2x80x9cnon xcex1-methyl vinyl monomer terminated with an xcex1-methyl vinyl monomerxe2x80x9d means that, when a vinyl monomer bearing no xcex1-methyl group is present, as polymerized units, in the macromonomer, the macromonomer must be terminated by a unit derived from an xcex1-methyl vinyl monomer. For example, while styrene might be present, as polymerized units, in a macromonomer chain, that macromonomer chain would be terminated by xcex1-methyl styrene, or some other xcex1-methyl vinyl monomer. Suitable xcex1-methyl vinyl monomers include, for example, methacrylate esters, such as C1 to C18 normal or branched alkyl esters of methacrylic acid, including methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, or stearyl methacrylate; hydroxyalkyl methacrylates such as hydroxyethyl methacrylate; glycidylmethacrylate; phenyl methacrylate; methacrylamide; methacrylonitrile; or combinations thereof.
One skilled in the art will recognize that there are many ways to prepare the macromonomer useful in the present invention. For example, the macromonomer may be prepared by a high temperature (e.g., at least 150xc2x0 C.) continuous process such as disclosed in U.S. Pat. No. 5,710,227 or EP-A-1,010,706, published Jun. 21, 2000. In a preferred continuous process, a reaction mixture of first ethylenically unsaturated monomers is passed through a heated zone having a temperature of at least 150xc2x0 C., and more preferably at least 275xc2x0 C. The heated zone may also be maintained at a pressure above atmospheric pressure (e.g., greater than 3,000 kPa=greater than 30 bar). The reaction mixture of monomers may also optionally contain a solvent such as water, acetone, methanol, isopropanol, propionic acid, acetic acid, dimethylformamide, dimethylsulfoxide, methylethylketone, or combinations thereof.
The macromonomer useful in the present invention may also be prepared by polymerizing first ethylenically unsaturated monomers in the presence of a free radical initiator and a catalytic metal chelate chain transfer agent (e.g., a transition metal chelate). Such a polymerization may be carried out by a solution, bulk, suspension, or emulsion polymerization process. Suitable methods for preparing the macromonomer using a catalytic metal chelate chain transfer agent are disclosed in for example U.S. Pat. Nos. 4,526,945, 4,680,354, 4,886,861, 5,028,677, 5,362,826, 5,721,330, and 5,756,605; European publications EP-A-0199,436, and EP-A-0196783; and PCT publications WO 87/03605, WO 96/15158, and WO 97/34934.
Preferably, the macromonomer useful in the present invention is prepared by an aqueous emulsion free radical polymerization process using a transition metal chelate complex. Preferably, the transition metal chelate complex is a cobalt (II) or (III) chelate complex such as, for example, dioxime complexes of cobalt (II), cobalt (II) porphyrin complexes, or cobalt (II) chelates of vicinal iminohydroxyimino compounds, dihydroxyimino compounds, diazadihydroxyiminodialkyldecadienes, or diazadihydroxyiminodialkylundecadienes, or combinations thereof. These complexes may optionally include bridging groups such as BF2, and may also be optionally coordinated with ligands such as water, alcohols, ketones, and nitrogen bases such as pyridine. Additional suitable transition metal complexes are disclosed in for example U.S. Pat. Nos. 4,694,054; 5,770,665; 5,962,609; and 5,602,220. A preferred cobalt chelate complex useful in the present invention is Co II (2,3-dioxyiminobutane-BF2)2, the Co III analogue of the aforementioned compound, or combinations thereof. The spatial arrangements of such complexes are disclosed in for example EP-A-199436 and U.S. Pat. No. 5,756,605.
In preparing macromonomer by an aqueous emulsion polymerization process using a transition metal chelate chain transfer agent, at least one first ethylenically unsaturated monomer is polymerized in the presence of a free radical initiator and the transition metal chelate according to conventional aqueous emulsion polymerization techniques. Preferably, the first ethylenically unsaturated monomer is an xcex1-methyl vinyl monomer as previously described herein.
The polymerization to form the macromonomer is preferably conducted at a temperature of from 20xc2x0 C. to 150xc2x0 C., and more preferably from 40xc2x0 C. to 95xc2x0 C. The solids level at the completion of the polymerization is typically from 5 weight percent to 70 weight percent, and more preferably from 30 weight percent to 60 weight percent, based on the total weight of the aqueous emulsion.
The concentration of initiator and transition metal chelate chain transfer agent used during the polymerization process is preferably chosen to obtain the desired degree of polymerization of the macromonomer. Preferably, the concentration of initiator is from 0.2 weight percent to 3 weight percent, and more preferably from 0.5 weight percent to 1.5 weight percent, based on the total weight of monomer. Preferably, the concentration of transition metal chelate chain transfer agent is from 5 ppm to 200 ppm, and more preferably from 10 ppm to 100 ppm, based on the total monomers used to form the macromonomer.
The first ethylenically unsaturated monomer, initiator, and transition metal chelate chain transfer agent may be added in any manner known to those skilled in the art to carry out the polymerization. For example, the monomer, initiator and transition metal chelate may all be present in the aqueous emulsion at the start of the polymerization process (i.e., a batch process). Alternatively, one or more of the components may be gradually fed to an aqueous solution (i.e., a continuous or semi-batch process). For example, it may be desired to gradually feed the entire or a portion of the initiator, monomer, and/or transition metal chelate to a solution containing water and surfactant. In a preferred embodiment, at least a portion of the monomer and transition metal chelate are gradually fed during the polymerization, with the remainder of the monomer and transition metal chelate being present in the aqueous emulsion at the start of the polymerization. In this embodiment, the monomer may be fed as is, or suspended or emulsified in an aqueous solution prior to being fed.
Any suitable free radical initiator may be used to prepare the macromonomer. The initiator is preferably selected based on such parameters as its solubility in one or more of the other components (e.g., monomers, water); half life at the desired polymerization temperature (preferably a half life within the range of from about 30 minutes to about 10 hours), and stability in the presence of the transition metal chelate. Suitable initiators include for example azo compounds such as 2,2xe2x80x2-azobis (isobutyronitrile), 4,4xe2x80x2-azobis(4-cyanovaleric acid), 2,2xe2x80x2-azobis [2-methyl-N-(1,1-bis(hydroxymethyl)-2-(hydroxyethyl)]-propionamide, and 2,2xe2x80x2-azobis [2-methyl-N-(2-hydroxyethyl)]-propionamide; peroxides such as t-butyl hydroperoxide, benzoyl peroxide; sodium, potassium, or ammonium persulphate or combinations thereof Redox initiator systems may also be used, such as for example persulphate or peroxide in combination with a reducing agent such as sodium metabisulphite, sodium bisulfite, sodium formaldehyde sulfoxylate, isoascorbic acid, or combinations thereof. Metal promoters, such as iron, may also optionally be used in such redox initiator systems. Also, buffers, such as sodium bicarbonate may be used as part of the initiator system.
An emulsifier is also preferably present during the aqueous emulsion polymerization process to prepare the macromonomer. Any emulsifier may be used that is effective in emulsifying the monomers such as for example anionic, cationic, or nonionic emulsifiers. In a preferred embodiment, the emulsifier is anionic such as for example sodium, potassium, or ammonium salts of dialkylsulphosuccinates; sodium, potassium, or ammonium salts of sulphated oils; sodium, potassium, or ammonium salts of alkyl sulphonic acids, such as sodium dodecyl benzene sulfonate; sodium, potassium, or ammonium salts of alkyl sulphates, such as sodium lauryl sulfate; ethoxylated alkyl ether sulfates; alkali metal salts of sulphonic acids; C12 to C24 fatty alcohols, ethoxylated fatty acids or fatty amides; sodium, potassium, or ammonium salts of fatty acids, such as Na stearate and Na oleate; or combinations thereof. The amount of emulsifier in the aqueous emulsion is preferably from 0.05 weight percent to 10 weight percent, and more preferably from 0.3 weight percent to 3 weight percent, based on the total weight of the monomers.
The macromonomer thus prepared is emulsion polymerized with at least one second ethylenically unsaturated monomer to form a copolymer composition containing graft copolymer particles. The polymerization is carried out by providing the macromonomer as water insoluble particles in a macromonomer aqueous emulsion and the second ethylenically unsaturated monomer in a monomer composition. At least a portion of the macromonomer aqueous emulsion is combined with at least a portion of the monomer composition to form a polymerization reaction mixture that is polymerized in the presence of an initiator.
Although in no way intending to be bound by theory, it is believed that by providing the macromonomer in the form of water insoluble macromonomer particles in an aqueous emulsion, and the second ethylenically unsaturated monomer in a separate monomer composition, upon combination, the second ethylenically unsaturated monomer diffuses through the aqueous phase and then into the macromonomer particles where the polymerization occurs. Preferably, the diffusion of the second ethylenically unsaturated monomer into the macromonomer particles is evidenced by swelling of the macromonomer particles. It is an essential feature of the invention that, prior to being combined with the monomer composition, the macromonomers are present in plural discrete particles dispersed in the aqueous phase. Preferably, these plural macromonomer particles have previously been formed by aqueous emulsion polymerization, and the resultant macromonomer aqueous emulsion is combined with the monomer composition and subsequently polymerized without being isolated. Addition of the monomer composition to the macromonomer aqueous emulsion results initially in the presence of plural monomer droplets in the aqueous emulsion as separate entities distributed among, but not in direct contact with, the plural macromonomer particles. That is, the monomer droplets are separated from the macromonomer particles, and from each other, by an aqueous phase. Individual monomer molecules must then exit the monomer droplet, dissolve in the aqueous phase, diffuse through that aqueous phase to a macromonomer particle, and enter that macromonomer particle where polymerization to form the graft copolymer (preferably, comb copolymer) occurs. Because the water insoluble macromonomers are unable to diffuse through the aqueous phase, it is essential that the monomer droplets not include water insoluble macromonomer if gel formation is to be avoided and if the number of particles initially established by the macromonomer particles is to be maintained during polymerization of monomers with macromonomers.
The macromonomer aqueous emulsion useful in the present invention may be formed in any manner known to those skilled in the art. For example, the macromonomer, produced by any known method, may be isolated as a solid (e.g., spray dried) and emulsified in water. Also, for example, the macromonomer, if prepared via an emulsion or aqueous based polymerization process, may be used as is, or diluted with water or concentrated to a desired solids level.
In a preferred embodiment of the present invention, the macromonomer aqueous emulsion is formed from the emulsion polymerization of at least one first ethylenically unsaturated monomer in the presence of a transition metal chelate chain transfer agent as described previously herein. This embodiment is preferred for numerous reasons. For example, the macromonomer polymerization can be readily controlled to produce a desired particle size distribution (preferably narrow, e.g., polydispersity less than 2). Also, for example, additional processing steps, such as isolating the macromonomer as a solid, can be avoided, leading to better process economics. In addition, the macromonomer, macromonomer aqueous emulsion, and the graft copolymer can be prepared by consecutive steps in a single reactor which is desirable in a commercial manufacturing facility because process parameters, such as manufacturing cost and particle size distribution, may be optimized.
The xe2x80x9cmacromonomer aqueous emulsionxe2x80x9d useful in the present invention contains from 20 weight percent to 60 weight percent, and more preferably from 30 weight percent to 50 weight percent of at least one water insoluble macromonomer, based on the total weight of macromonomer aqueous emulsion. The macromonomer aqueous emulsion may also contain mixtures of macromonomer. Preferably, the macromonomer aqueous emulsion contains less than 5 weight percent and more preferably less than 1 weight percent of ethylenically unsaturated monomer, based on the total weight of macromonomer aqueous emulsion.
The water insoluble macromonomer particles have a particle size chosen such that, upon addition of monomers, particles of graft copolymer having a desired particle size will be formed. For example, the final graft copolymer particle size is directly proportional to the initial particle size of the macromonomer and the concentration of second ethylenically unsaturated monomer in the polymerization reaction mixture, assuming all the particles participate equally in the polymerization. Preferably, the macromonomer particles have a weight average particle size of from 50 nm to 500 nm, and more preferably from 80 nm to 200 nm as measured by Capillary Hydrodynamic Fractionation technique using a Matec CHDF 2000 particle size analyzer equipped with a HPLC type Ultra-violet detector.
The macromonomer aqueous emulsion may also include one or more emulsifying agents. The type and amount of emulsifying agent is preferably selected in a manner to produce the desired particle size. Suitable emulsifying agents include those previously disclosed for use in preparing the macromonomer by an emulsion polymerization process. Preferred emulsifying agents are anionic surfactants such as, for example, sodium lauryl sulfate, sodium dodecylbenzene sulfonate, sulfated and ethoxylated derivatives of nonylphenols and fatty alcohols. The total level of emulsifying agent, based on the total weight of macromonomer is preferably from 0.2 weight percent to 5 weight percent and more preferably from 0.5 weight percent to 2 weight percent.
The xe2x80x9cmonomer compositionxe2x80x9d useful in the present invention contains at least one kind of ethylenically unsaturated monomer. The monomer composition may contain all (i.e., 100%) monomer, or contain monomer dissolved or dispersed in an organic solvent and/or water. Preferably, the level of monomer in the monomer composition is from 50 weight percent to 100 weight percent, more preferably from 60 to 90 weight percent, and most preferably from 70 to 80 weight percent, based on the total weight of the monomer composition. Examples of organic solvents that may be present in the monomer composition include C6 to C14 alkanes. The organic solvent in the monomer composition will be no more than 30 weight percent, and more preferably no more than 5 weight percent, based on the total weight of the monomer composition.
In addition to water and/or organic solvent, the monomer composition may also optionally contain monomers containing functional groups, such as, for example, monomers containing hydroxy, amido, aldehyde, ureido, polyether, glycidylalkyl, keto groups or combinations thereof. These other monomers are generally present in the monomer composition at a level of from 0.5 weight percent to 15 weight percent, and more preferably from 1 weight percent to 3 weight percent based on the total weight of the graft copolymer. Examples of functional monomers include ketofunctional monomers such as the acetoacetoxy esters of hydroxyalkyl acrylates and methacrylates (e.g., acetoacetoxyethyl methacrylate) and keto-containing amides (e.g., diacetone acrylamide); allyl alkyl methacrylates or acrylates; glycidylalkyl methacrylates or acrylates; or combinations thereof. Such functional monomer can provide crosslinking if desired.
In a preferred embodiment, the monomers in the monomer composition are pre-emulsified in water to form a xe2x80x9cmonomer aqueous emulsionxe2x80x9d. Preferably, the monomer aqueous emulsion contains monomer droplets having a droplet size from 1 micron to 100 microns, and more preferably from 5 micron to 50 microns. Any suitable emulsifying agent may be used, for example those previously described, to emulsify the monomer to the desired monomer droplet size. Preferably, the level of emulsifying agent, if present, will be from 0.2 weight percent to 2 weight percent based on the total weight of monomer in the monomer composition.
The second ethylenically unsaturated monomer of the monomer composition is preferably selected to provide the desired properties in the resulting graft copolymer (i.e., copolymer) composition. Suitable ethylenically unsaturated monomers include for example methacrylate esters, such as C1 to C18 normal or branched alkyl esters of methacrylic acid, including methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate, isobornyl methacrylate; acrylate esters, such as C1 to C18 normal or branched alkyl esters of acrylic acid, including methyl acrylate, ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate; styrene; substituted styrenes, such as methyl styrene, a-methyl styrene or t-butyl styrene; olefinically unsaturated nitriles, such as acrylonitrile or metbacrylonitrile; olefinically unsaturated halides, such as vinyl chloride, vinylidene chloride or vinyl fluoride; vinyl esters of organic acids, such as vinyl acetate; N-vinyl compounds such as N-vinyl pyrrolidone; acrylamide; methacrylamide; substituted acrylamides; substituted methacrylamides; hydroxyalkylmethacrylates such as hydroxyethylmethacrylate; hydroxyalkylacrylates; dienes such as 1,3-butadiene and isoprene; vinyl ethers; or combinations thereof. The ethylenically unsaturated monomer can also be an acid containing monomer or a functional monomer, such as those previously described herein. Preferably, the ethylenically unsaturated monomer of the monomer composition does not contain amino groups.
If the monomers (i.e., the second ethylenically unsaturated monomers) of the monomer composition will be used to prepare the backbone of a comb copolymer, the graft segment of which is not miscible with the thermoplastic polymer of the present invention, it is required that the composition of the those monomers be chosen such that the backbone of the comb copolymer formed therefrom will be miscible in the thermoplastic polymer. If the graft segment is miscible with the thermoplastic polymer, the backbone may, optionally, be miscible in the thermoplastic polymer. The composition of the monomers of the monomer composition further should be chosen so that the Tg of the backbone of the comb copolymer formed therefrom will be preferably from xe2x88x9265xc2x0 C. to 180xc2x0 C., more preferably from xe2x88x9245xc2x0 C. to 180xc2x0 C., and most preferably from xe2x88x9220 xc2x0 C. to 130xc2x0 C.
In a preferred embodiment, the monomer composition includes one or more ethylenically unsaturated monomers selected from C1 to C18 normal or branched alkyl esters of acrylic acid, including methyl acrylate, ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate; styrene; substituted styrenes, such as methyl styrene, xcex1-methyl styrene or t-butyl styrene; butadiene or combinations thereof.
As previously mentioned, the macromonomer aqueous emulsion and monomer composition are combined to form a xe2x80x9cpolymerization reaction mixturexe2x80x9d, and polymerized in the presence of a free radical initiator to form an xe2x80x9caqueous copolymer compositionxe2x80x9d, also referred to herein as an xe2x80x9caqueous dispersion of a segmental copolymerxe2x80x9d. The term xe2x80x9cpolymerization reaction mixture,xe2x80x9d as used herein, refers to the resulting mixture formed when at least a portion of the macromonomer aqueous emulsion and at least a portion of the monomer composition are combined. The polymerization reaction mixture may also contain initiator or any other additive used during the polymerization. Thus, the polymerization reaction mixture is a mixture that changes in composition as the macromonomer and monomer in the monomer composition are reacted to form graft copolymer.
The macromonomer aqueous emulsion and monomer composition may be combined in various ways to carry out the polymerization. For example, the macromonomer aqueous emulsion and the monomer composition may be combined prior to the start of the polymerization reaction to form the polymerization reaction mixture. Alternatively, the monomer composition could be gradually fed into the macromonomer aqueous emulsion, or the macromonomer aqueous emulsion could be gradually fed into the monomer composition. It is also possible that only a portion of the macromonomer aqueous emulsion and/or monomer composition be combined prior to the start of the polymerization with the remaining monomer composition and/or macromonomer aqueous emulsion being fed during the polymerization.
The initiator can also be added in various ways. For example, the initiator may be added in xe2x80x9cone shotxe2x80x9d to the macromonomer aqueous emulsion, the monomer composition, or a mixture of the macromonomer aqueous emulsion and the monomer composition at the start of the polymerization. Alternatively, all or a portion of the initiator can be co-fed as a separate feed stream, as part of the macromonomer aqueous emulsion, as part of the monomer composition, or any combination of these methods.
The preferred method of combining the macromonomer aqueous emulsion, the monomer composition, and initiator will depend on such factors as the desired graft copolymer composition. For example, the distribution of the macromonomer as a graft along the backbone can be affected by the concentrations of both the macromonomer and the second ethylenically unsaturated monomers at the time of the polymerization. In this regard, a batch process will afford high concentration of both the macromonomer and the second ethylenically unsaturated monomers at the onset of the polymerization whereas a semi-continuous process will keep the second ethylenically unsaturated monomer concentration low during the polymerization. Thus, through the method by which the macromonomer aqueous emulsion and monomer composition are combined, it is possible to control, for example: the number of graft segments, derived from macromonomer, per polymer chain; the distribution of graft segments in each chain, and the length of the polymer backbone.
Initiators useful in polymerizing the macromonomer and second ethylenically unsaturated monomer include any suitable initiator for emulsion polymerizations known to those skilled in the art. The selection of the initiator will depend on such factors as the initiator""s solubility in one or more of the reaction components (e.g. monomer, macromonomer, water); and half life at the desired polymerization temperature (preferably a half life within the range of from about 30 minutes to about 10 hours). Suitable initiators include those previously described herein in connection with forming the macromonomer, such as azo compounds such as 4,4xe2x80x2-azobis(4-cyanovaleric acid), peroxides such as t-butyl hydroperoxide; sodium, potassium, or ammonium persulfate; redox initiator systems such as, for example, persulphate or peroxide in combination with a reducing agent such as sodium metabisulfite, sodium bisulfite, sodium formaldehyde sulfoxylate, isoascorbic acid; or combinations thereof. Metal promoters, such as iron; and buffers, such as sodium bicarbonate, may also be used in combination with the initiator. Additionally, Controlled Free Radical Polymerization (CFRP) methods such as Atom Transfer Radical Polymerization; or Nitroxide Mediated Radical Polymerization may be used. Preferred initiators include azo compounds such as 4,4xe2x80x2-azobis(4-cyanovaleric acid).
The amount of initiator used will depend on such factors as the copolymer desired and the initiator selected. Preferably, from 0.1 weight percent to 1 weight percent initiator is used, based on the total weight of monomer and macromonomer.
The polymerization temperature will depend on the type of initiator chosen and desired polymerization rates. Preferably, however, the macromonomer and second ethylenically unsaturated monomer are polymerized at a temperature of from 0xc2x0 C. to 150xc2x0 C., and more preferably from 20xc2x0 C. to 95xc2x0 C.
The amount of macromonomer aqueous emulsion and monomer composition added to form the polymerization reaction mixture will depend on such factors as the concentrations of macromonomer and second ethylenically unsaturated monomer in the macromonomer aqueous emulsion and monomer composition, respectively, and the desired graft copolymer composition. Preferably, the macromonomer aqueous emulsion and monomer composition are added in amounts to provide a graft copolymer containing as polymerized units from 20 weight percent to 80 weight percent, more preferably from 30 weight percent to 70 weight percent, and most preferably from 40 weight percent to 60 weight percent macromonomer as polymerized graft segment, and from 20 weight percent to 80 weight percent, more preferably from 30 weight percent to 70 weight percent and most preferably from 40 weight percent to 60 weight percent second ethylenically unsaturated monomer as polymerized units of the backbone.
One skilled in the art will recognize that other components used in conventional emulsion polymerizations may optionally be used in the method of the present invention. For example, to reduce the molecular weight of the resulting graft copolymer, the polymerization may optionally be conducted in the presence of one or more chain transfer agents, such as n-dodecyl mercaptan, thiophenol; halogen compounds such as bromotrichloromethane; or combinations thereof. Also, additional initiator and/or catalyst may be added to the polymerization reaction mixture at the completion of the polymerization reaction to reduce any residual monomer, (e.g., chasing agents). Suitable initiators or catalysts include those initiators previously described herein. In addition, the chain transfer capacity of a macromonomer through addition-fragmentation can be utilized in part to reduce molecular weight through appropriate design of monomer compositions and polymerization conditions. See e.g, E. Rizzardo, et. al., Prog. Pacific Polym. Sci., 1991, 1, 77-88; G. Moad, et. al., WO 96/15157.
Preferably, the process of the present invention does not require neutralization of the monomer, or resulting aqueous graft copolymer composition. These components preferably remain in unneutralized form (e.g., no neutralization with a base if acid functional groups are present).
The resulting aqueous graft copolymer composition formed by polymerization of the macromonomer and the ethylenically unsaturated monomer in the monomer composition preferably has a solids level of from 30 weight percent to 70 weight percent and more preferably from 40 weight percent to 60 weight percent. The aqueous graft copolymer composition preferably contains graft copolymer particles that are water insoluble and have a particle size of from 60 nm to 500 nm, and more preferably from 80 nm to 350 nm.
The graft copolymer formed preferably has a backbone containing, as polymerized units, the second ethylenically unsaturated monomer from the monomer composition, and one or more macromonomer units, as polymerized units, wherein a terminal ethylenically unsaturated group of the macromonomer is incorporated into the backbone and the remainder of the macromonomer becomes a graft segment pendant to the backbone (i.e., a side chain) upon polymerization. Preferably, each side chain is a graft segment derived from the grafting of one macromonomer to the backbone. The degree of polymerization of the graft segments derived from the macromonomer is preferably from 10 to 1,000, more preferably from 20 to 1,000, and most preferably from 20 to 200, where the degree of polymerization is expressed as the number of polymerized units of ethylenically unsaturated monomer used to form the macromonomer. The weight average molecular weight of the graft copolymer (e.g., of the comb copolymer) is preferably in the range of from 50,000 to 2,000,000, and more preferably from 100,000 to 1,000,000. The number average molecular weight of a comb copolymer is typically less than the corresponding weight average molecular weight. The number average molecular weights of the comb copolymers of the present invention are at least 25,000, and typically range from 25,000 to 600,000. Molecular weights as used herein can be determined by size exclusion chromatography (SEC), also known as gel permeation chromatography (GPC).
In a preferred embodiment of the present invention, the polymerization is conducted in two stages. In the first stage, the macromonomer is formed in an aqueous emulsion polymerization process, and in the second stage the macromonomer is polymerized with the second ethylenically unsaturated monomer in an emulsion. For efficiency, preferably these two stages are conducted in a single vessel. For example, in the first stage, the macromonomer aqueous emulsion may be formed by polymerizing in an aqueous emulsion at least one first ethylenically unsaturated monomer to form water insoluble macromonomer particles. This first stage polymerization is preferably conducted using a transition metal chelate chain transfer agent as previously described herein. After forming the macromonomer aqueous emulsion, a second emulsion polymerization is preferably performed in the same vessel to polymerize the macromonomer with at least one second ethylenically unsaturated monomer. This second stage may be conducted for example by directly adding (e.g., all at once or by a gradual feed) the monomer composition and initiator to the macromonomer aqueous emulsion. One main advantage of this embodiment is that the macromonomer does not have to be isolated, and the second polymerization can take place simply by adding the monomer composition and initiator to the macromonomer aqueous emulsion. In this preferred embodiment, the particle size and particle size distribution of the plural water insoluble macromonomer particles may be precisely controlled, and later addition of more macromonomer aqueous emulsion would typically not be required, except when, for example, a second mode (particle size and/or composition) of graft copolymer is desired.
In another preferred embodiment of the present invention, the polymerization of the macromonomer and second ethylenically unsaturated monomer is at least partially performed in the presence of an acid containing monomer, acid containing macromonomer, or combinations thereof. The acid containing monomer or acid containing macromonomer may be added in any manner to the polymerization reaction mixture. Preferably, the acid containing monomer or acid containing macromonomer is present in the monomer composition. The acid containing monomer or acid containing macromonomer may also be added as a separate stream to the polymerization reaction mixture.
The amount of acid containing monomer or acid containing macromonomer added to the polymerization reaction mixture is preferably from 0.2 weight percent to 10 weight percent, more preferably from 0.5 weight percent to 5 weight percent, and most preferably from 1 weight percent to 2 weight percent, based on the total weight of monomer and macromonomer added to the polymerization reaction mixture.
Acid containing monomers which may be used in this embodiment include ethylenically unsaturated monomers bearing acid functional or acid forming groups such as those previously described herein. The xe2x80x9cacid containing macromonomerxe2x80x9d useful in this embodiment is any low molecular weight polymer having at least one terminal ethylenically unsaturated group that is capable of being polymerized in a free radical polymerization process, and that is formed from at least one kind of acid containing monomer. Preferably, the amount of acid containing monomer present, as polymerized units, in the acid containing macromonomer is from 50 weight percent to 100 weight percent, more preferably from 90 weight percent to 100 weight percent, and most preferably from 95 weight percent to 100 weight percent.
The acid containing macromonomer may be prepared according to any technique known to those skilled in the art such as those previously described herein. In a preferred embodiment of the present invention, the acid containing macromonomer is prepared by a solution polymerization process using a free radical initiator and transition metal chelate complex. Such a process is disclosed in, for example, U.S. Pat. No. 5,721,330. Preferred acid containing monomers used to form the acid containing macromonomer are xcex1-methyl vinyl monomers such as methacrylic acid.
In another preferred embodiment of the present invention, a xe2x80x9cmacromolecular organic compoundxe2x80x9d having a hydrophobic cavity is present in the polymerization medium used to form the macromonomer and/or aqueous copolymer composition. Preferably, the macromolecular organic compound is used when copolymerizing ethylenically unsaturated monomers with very low water solubility such as lauryl or stearyl acrylates and/or methacrylates. By xe2x80x9cvery low water solubilityxe2x80x9d it is meant a water solubility at 25xc2x0 C. to 50xc2x0 C. of no greater than 50 millimoles/liter. For example, the macromolecular organic compound may be added to the monomer composition, the macromonomer aqueous emulsion, or the polymerization reaction mixture used to form the aqueous copolymer composition. Also, for example, the macromolecular organic compound may be added to an aqueous emulsion of ethylenically unsaturated monomer used to form the macromonomer. Suitable techniques for using a macromolecular organic compound having a hydrophobic cavity are disclosed in, for example, U.S. Pat. No. 5,521,266.
Preferably, the macromolecular organic compound having a hydrophobic cavity is added to the polymerization reaction mixture to provide a molar ratio of macromolecular organic compound to very low water solubility monomer or macromonomer of from 5:1 to 1:5000 and more preferably from 1:1 to 1:500.
Macromolecular organic compounds having a hydrophobic cavity useful in the present invention include for example cyclodextrin or cyclodextrin derivatives; cyclic oligosaccharides having a hydrophobic cavity such as cycloinulohexose, cycloinuloheptose, or cycloinuloctose; calyxarenes; cavitands; or combinations thereof. Preferably, the macromolecular organic compound is xcex2-cyclodextrin, more preferably methyl-xcex2-cyclodextrin.
Monomers having low water solubility include for example primary alkenes; styrene and alkylsubstituted styrene; xcex1-methyl styrene; vinyltoluene; vinyl esters of C4 to C30 carboxylic acids, such as vinyl 2-ethylhexanoate, vinyl neodecanoate; vinyl chloride; vinylidene chloride; N-alkyl substituted (meth)acrylamide such as octyl acrylamide and maleic acid amide; vinyl alkyl or aryl ethers with (C3-C30) alkyl groups such as stearyl vinyl ether; (C1-C30) alkyl esters of (meth)acrylic acid, such as methyl methacrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, benzyl (meth)acrylate, lauryl (meth)acrylate, oleyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate; unsaturated vinyl esters of (meth)acrylic acid such as those derived from fatty acids and fatty alcohols; multifunctional monomers such as pentaerythritol triacrylate; monomers derived from cholesterol or combinations thereof.
The aqueous methods used to produce the comb copolymer of the present invention may produce an aqueous copolymer composition containing water insoluble particles of comb copolymer. The comb copolymer particles preferably have a weight average particle size of from 50 nm to 500 nm, and more preferably from 80 nm to 350 nm.
Preferably, the particles of comb copolymer contain from 20 weight percent to 80 weight percent, more preferably from 30 to 70 weight percent, and most preferably from 40 to 60 weight percent polymerized units of a macromonomer, based on the total weight of the copolymer, where the macromonomer preferably has a composition as previously described herein for the water insoluble macromonomer present in the macromonomer aqueous emulsion. The comb copolymer particles also preferably contain from 20 weight percent to 80 weight percent, more preferably from 30 to 70 weight percent, and most preferably from 40 to 60 weight percent polymerized units of at least one second ethylenically unsaturated monomer, based on the total weight of the copolymer. The second ethylenically unsaturated monomer may be any ethylenically unsaturated monomer that provides desirable properties in the copolymer particles, such as those useful in the monomer composition as previously described herein.
Although the backbone of the comb copolymer may be branched, with such branching including, for example, xe2x80x9cstarxe2x80x9d structures, it is preferred that the backbone is linear. Compositionally, the backbone of the copolymer preferably contains polymerized units of the second ethylenically unsaturated monomer derived from the monomer composition.
Preferably, the Tg of the backbone of the comb copolymer of the present invention is from xe2x88x9265xc2x0 C. to 180xc2x0 C., more preferably from xe2x88x9245xc2x0 C. to 180xc2x0 C., and most preferably from xe2x88x9220xc2x0 C. to 130xc2x0 C. It is further required that, if the graft segment of the comb copolymer is not miscible with the thermoplastic polymer of the present invention, the backbone is miscible with that thermoplastic polymer.
The pendant graft segments of the graft copolymer preferably contain polymerized units of the macromonomer. In a preferred embodiment of the present invention, each graft segment is derived from one macromonomer. Additionally, the pendant graft segments contain less than 5 weight percent and more preferably less than 1 weight percent of the polymerized second ethylenically unsaturated monomer derived from the monomer composition, based on the total weight of the pendant graft segments.
Preferably, the Tg of the graft segment is from xe2x88x9265xc2x0 C. to 180xc2x0 C., more preferably from xe2x88x9245xc2x0 C. to 180xc2x0 C., and most preferably from xe2x88x9220xc2x0 C to 130xc2x0 C. It is further required that, if the backbone of the comb copolymer is not miscible with the thermoplastic polymer of the present invention, the graft segment is miscible with that thermoplastic polymer.
Preferably, the overall weight average molecular weight of the comb copolymer is from 50,000 to 2,000,000, and more preferably from 100,000 to 1,000,000.
In a preferred embodiment of the present invention, the water insoluble graft copolymer particles further contain from 0.2 weight percent to 10 weight percent, more preferably from 0.5 weight percent to 5 weight percent, and most preferably from 1 weight percent to 2 weight percent of an acid containing macromonomer, based on the total weight of the graft copolymer. The acid containing macromonomer preferably has a composition as previously described herein.
Although in no way intending to be bound by theory, it is believed that the xe2x80x9cacid containing macromonomerxe2x80x9d is attached to the surface of the water insoluble graft copolymer particles and provides stability. By xe2x80x9cattached,xe2x80x9d as used herein, it is believed that the acid containing macromonomer is bound in some manner (e.g., covalent, hydrogen bonding, ionic) to a polymer chain in the particle. Preferably, the acid containing macromonomer is covalently bound to a polymer chain in the particle. It has been found that the acid containing macromonomer provides stability to the particles such that the aqueous copolymer composition produced exhibits unexpected improved shear stability; freeze thaw stability; and stability to additives in formulations, as well as reduction of coagulum during the polymerization. Although improved stability can be achieved using acid containing monomer, these benefits are most dramatic when an acid containing macromonomer is used.
When the segmental copolymer of the present invention is a block copolymer, at least one block (i.e., copolymer segment) must be miscible with the thermoplastic polymer of the present invention.
The segmental copolymers of the present invention may be isolated as powders, or other solid particles, from dispersions containing them (e.g., aqueous emulsions) by methods well known in the art. These methods include, for example, spray drying, coagulation and oven drying, and freeze drying. For purposes of isolation, handling, storage, shipping, and blending of the segmental copolymer, it is preferred that either the backbone or graft segment have a Tg of at least 30xc2x0 C., more preferably from 50xc2x0 C. to 180xc2x0 C., and most preferably from 70xc2x0 C. to 130xc2x0 C.
The segmental copolymer of the present invention are, for example, blended with the thermoplastic polymer to form a solids blend that is mixed and heated to form uniform melt blends containing the segmental copolymer at a level of, preferably, 0.5 to 10 PHR and more preferably 1 to 10 PHR. Used herein, xe2x80x9cPHRxe2x80x9d refers to parts by weigh per hundred part by weight of thermoplastic polymer. The melt blends are then shaped and cooled, typically to room temp, and preferably to below the desired use temperature of the article so formed.
The melt blend is shaped to form the thermoplastic article of the present invention by any technique common to the art. Equipment used to shape the melt blend includes, for example, dies, presses, molds, and blow molds. The articles thus formed are typically cooled to room temperature. The articles of the present invention may further be laminated to other thermoplastic compositions or thermoset compositions by techniques know in the art, such as, for example, co-extrusion. The article of the present invention may also be affixed directly to other substrates, such as for example wood or metal, with or without the use of an adhesive. Any type of thermoplastic article common to the art may be made by the method of the present invention. A non-exhaustive list of these articles includes, for example: construction materials, such as siding, gutters, downspouts, pipe, pipe fittings, wallboard, wall-coverings, molding, fencing, decking, window frames and profiles; consumer goods such as bottles, jars, other containers, films, and laminates; appliance housing such as housings for computers, refrigerators, and air conditioners, as well as interior appliance parts; both interior and exterior automotive parts such as body side molding, and instrument and door panels; packaging materials; rigid film and sheet such as credit cards and computer disks; toys; and plastic parts such as screws, gears, and wires.
The preferred thermoplastic polymers, and the polymers which are most effectively modified by the segmental copolymers of the present invention, are the homopolymers of vinyl chloride and copolymers of vinyl chloride and vinyl acetate. More preferred are the homopolymers of vinyl chloride and copolymers of vinyl chloride and vinyl acetate. Poly(vinyl chloride) is the most preferred thermoplastic polymer.
Solids blends of the segmental copolymer and the thermoplastic polymer can be accomplished by any convenient technique. Dry mixing techniques, as with a mechanical mixer-blender device, may be employed. The powder blends can, if desired, be processed in commercial extrusion equipment at conditions varying with the molecular weight of the polyvinyl halide used and the equipment employed for that purpose.
Certain lubricants, stabilizers, and the like are often incorporated in the blends. The stabilizers serve to prevent the breakdown of the polyvinyl halide and are of several different types. Two varieties stabilize against thermal and ultraviolet light stimulated oxidative degradation, discoloration, and the like.
Other additives to the blends prepared in accordance with the present invention may include, for example, colorants, including organic dyes, such as anthraquinone red; organic pigments and lakes such as phthalocyanine blue; inorganic pigments such as titanium dioxide, and cadmium sulfide; fillers and particulate extenders such as carbon black, amorphous silica, asbestos, glass fibers, and magnesium carbonate; plasticizers such as dioctyl phthalate, dibenzyl phthalate, butyl benzyl phthalate, and hydrocarbon oils; and impact modifiers such as typical core-shell methacrylate/butadiene/styrene modifiers and core shell acrylate/methacrylate modifiers.
While only a few of such materials have been specifically recited, it is not intended to exclude others; the recitation is exemplary only, and each category of additives is common and well-known in the art. The inclusions can be made at any stage of preparation in. accordance with accepted techniques well-known to those ordinarily skilled in the art, in proportions which are commonly employed. Such additional materials are not of particular significance in the present invention.
Experimental
Molecular Weight Determination Using Gel Permeation Chromatography (GPC)
Gel Permeation Chromatography, otherwise known as size exclusion chromatography, actually separates the members of a distribution of polymer chains according to their hydrodynamic size in solution rather than their molar mass. The system is then calibrated with standards of known molecular weight and composition to correlate elution time with molecular weight. The techniques of GPC are discussed in detail in Modern Size Exclusion Chromatography, W. W. Yau, J. J Kirkland, D. D. Bly; Wiley-Interscience, 1979, and in A Guide to Materials Characterization and Chemical Analysis, J. P. Sibilia; VCH, 1988, p.81-84.
For example, the molecular weight information for a low molecular weight sample (e.g., 10,000) may be determined as follows: The sample (an aqueous emulsion containing low molecular weight particles) is dissolved in THF at a concentration of approximately 0.1% weight sample per volume THF, and shaken for 6 hours, followed by filtration through a 0.45 xcexcm PTFE (polytetrafluoroethylene) membrane filter. The analysis is performed by injecting 100 xcexcl of the above solution onto 3 columns, connected in sequence and held at 40xc2x0 C. The three columns are: one each of PL Gel 5 100, PL Gel 5 1,000, and PL Gel 5 10,000, all available from Polymer Labs, Amherst, Mass. The mobile phase used is THF flowing at 1 ml/min. Detection is via differential refractive index. The system was calibrated with narrow polystyrene standards. PMMA-equivalent molecular weights for the sample are calculated via Mark-Houwink correction using K=14.1xc3x9710xe2x88x923 ml/g and a=0.70 for the polystyrene standards and K=10.4xc3x9710xe2x88x923 ml/g and a=0.697 for the sample.