Polychloroprene elastomer
United States Patent [191 Kitagawa et al.  
 [451 Apr. 8, 1975 POLYCHLOROPRENE ELASTOMER [73] Assignee: Denki Kagaku Kogyo Kabushiki Kaisha, Tokyo, Japan [22] Filed: Sept. 18, 1972 [2l] Appl. No.: 289,915  
 Related US. Application Data [62] Division of Ser. No. 753,765, Aug. 1968, Pat. No,  
 [52] US. Cl. 260/890; 260/29.7 D; 260/33.6 A; 260/78.5 BB; 260/78.5 UA; 260/79.3 M; 260/82.l; 260/83.5; 260/83.7;  
  511 rm. Cl. cos: 29/12 [58] Field of Search 260/890 [56] References Cited UNITED STATES PATENTS 3.714.296 1/1973 Kitagawa et al. 260/890 Primary Examiner-+Murray Tillman Assistant Examiner-J. Ziegler Attorney, Agent, or FirmSughrue, Rothwell, Mion, Zinn &amp; Macpeak [57] ABSTRACT A process is disclosed for preparing a polychloroprene elastomer consisting of a blend of from 20 to 80 parts by weight of (a) a toluene-insoluble gel polymer and from 80 to 20 parts by weight of (b) a toluene-soluble sol polymer, the process comprising preparing the toluene-insoluble gel polymer by polymerizing chloroprene or a mixture of chloroprene with a small amount of at least one copolymerizable monomer in the presence of a suitable cross-linking agent, preparing the toluene-soluble sol polymer by polymerizing chloroprene or a mixture of chloroprene with a small amount of at least one copolymerizable monomer and blending the gel and sol polymers wherein an improved elastomer is obtained by polymerizing the toluene-insoluble gel polymer to a cross-linking density of at least 2.4 X 10 to a monomer conversion of at least 80%.  
 9 Claims, N0 Drawings 1 POLYCHLOROPRENE ELASTOMER i This is a division of application $61. No. 753,765, filed Aug. 19, 1968, now us. Pat. No. 3,714,296.  
 BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a polychloroprene elastomer having excellent extrusion and molding properties.  
 2. Description of the Prior Art The term polychloroprene elastomer or chloroprene as used herein refers to polymers of 2-chloro- 1,3-butadiene or copolymers of 2-chlorol ,3-butadiene with one or moe copolymerizable monomers.  
 Ordinary polychloroprene elastomers do not possess satisfactory processability characteristics especially for extrusion molding processes. Generally, it is not characterized by reduced die swell on extrusion through the rolls of the extrusion machines, by resistance to deformation, by smoothness of surface of extruded products, high velocity of extrusion and other factors as would be desirable. Accordingly, it is difficult to fabricate polychloroprene elastomers into shaped articles having complicated contours with any degree of precision by extrusion or by calendering. That is to say, that when manufacturing extruded products having a complicated figure and some resiliency, certain defects appear, namely, deformation, dimension changes, surface roughness, edge napping and the like.  
  It is an object of the present invention to provide a polychloroprene elastomer which is free from such defects and which is characterized by an improved processability, and excellent extrusion and molding properties. In more detail, the object of the present invention is to provide a polychloroprene elastomer which has excellent extrusion and molding properties as well as other improved processing properties such that it can be fabricated at a high extrusion rate into a smooth-surfaced extruded product which is free from any deformation or warp even though the product has a complicated cross-section.  
 SUMMARY OF THE INVENTION Thepresent invention comprises preparing a polychloroprene elastomer by blending a crosslinked toluene-insoluble gel-like polychloroprene (hereinafter referred to as the fgelpolymer), obtained by polymerizing chloroprene in the presence of a crosslinking agent, with a toluene-soluble sol-like polychloroprene (hereinafter referred to as sol polymer), obtained by ordinary polymerization procedures.  
 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS product. On the other hand, incorporation in a lesser 2 amount will result in unsatisfactory surface smoothness and a reduced flow property of the resulting elastomer and, consequently, a&#39;decreased extrusion rate.  
  more comonomers in the presence of a bifunctional crosslinking agent such as glycol dimethacrylates of the formula CH l wherein n is an integer of from 1 to 8, or  
 wherein n is an integer of from 2 to 4. Examples of suitable crosslinking agents include ethylene glycol dimethacrylate (EDMA), trimethylene glycol dimethacrylate, tetramethylene glycol dimethacrylate (TDMA),  
 diethylene glycol dimethacrylate (DEDMA), triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate (TEDMA) and the like; and divinylbenzene,  
 divinyl ether, diallyl phthalate, divinylsulfone and the like. The excellent extrusion and molding properties of the elastomer of the present invention are obtainable by the use of a highly crosslinked gel polymer having a crosslinking density of at least 2.4 X 10&#39;. If the density is less than 2.4 X 10&#39; the die swelling on extrusion will increase, the extrusion rate will decrease, the surface smoothness of the extruded product will be lost and, thus, the material will be poorly extruded. The crosslinking density of gel polymer depends on the type and quantity of crosslinking agent used, the degree of l monomer to polymer conversion and other factors,  
 and, therefore, the desired value is obtainable by properly adjusting these factors. 7 I The swelling index and crosslinking density of the crosslinked gel polymer are determined in the follow ing manner: The weight Wa of a sample is weighed by means&#39;of a chemical balance and the sample is soaked in about cc of toluene contained in a stoppered 100 cc measuring flask. The container is allowed to stand in a thermostat controlled bath of 30C. After reaching swelling equilibrium, the sample isremoved from the toluene, lightly wiped with filter paper, and  
 quickly weighed. The weight (WB) after swelling was noted and the swelling index (Q) was calculated by the equation Q= (ai -i) (Q) where P is the density (g/cc) of gel chloroprene, P is the density (g/cc) oftoluene. The crosslinking density /Wa 1) l/P2) where V, is the volume fraction of solvent toluene, V is the volume fraction of polychloroprene in the swollen gel and p. is interaction coefficient between polychloroprene and solvent.  
  The sol polymer used in the present invention may be obtained by polymerizing chloroprene or a mixture of chloroprene with small amounts of one or more copolymerizable monomers in the presence of an aliphatic mercaptan such as n-dodecylmercaptan. The resulting polymer is substantially gel-free and has a Mooney viscosity (ML, at 100C. of at least 15.  
  In the present invention there may be used as a comonomer copolymerizable with chloroprene, e.g., styrene, vinyltoluene, butadiene, isoprene 2,3- dichlorobutadiene-l ,3, methyl vinyl ketone, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, and acrylonitrile.  
  The gel polymer and sol polymer thus obtained are blended in the form of a latex in the proportion as mentioned above and the mixture is isolated by freeze coagulation or by similar conventional techniques or by drum drying to obtain a polychloroprene elastomer having a Mooney viscosity (ML, at 100C. of 30 to 70, preferably of 40 to 60.  
  The chloroprene elastomer thus obtained is thixotropic namely, when the elastomer is directly dissolved in benzene only the sol component dissolves and the gel component remains undissolved, when the elastomer is dissolved in benzene after mastication on a roll it dissolves entirely providing a turbid benzene solution which insolubilizes again after a few hours when allowed to stand still at room temperature. The gel polymer by itself is not solubilized by mastication, and this is a peculiar property obtained by blending with a low molecular sol polymer. All gel polymers do not exhibit such property when blended with a sol polymer, for instance, a gel polymer prepared by treating a chloroprene rubber with a peroxide will not exhibit such property.  
  The greatest characteristic of the rubber obtained by blending a gel polymer with a sol polymer in accordance with the present invention is the thixotropic property as mentioned above. It seems that the excellent extrusion molding property is attributable to this peculiar property since the low molecular sol polymer acts as a plasticizer on extrusion and the thixotropic gel polymer acts to prevent deformation, shrinkage and swelling. As a result of the interaction of the two polymers, the elastomer of the present invention exhibits good flow properties and good processability on extrusion and provides a good extruded product having a reduced deformation and die swelling tendency.  
  The present invention will now be illustrated by the following example which is not intended to be limiting in any manner. All parts are by weight.  
 EXAMPLE A. Preparation of sol polymer:  
  A polymerization mixture of the following recipe was charged into a stirred jacketed polymerization vessel and gradually heated, with stirring, to 40C. over a pcriod of one hour. A mixed aqueous solution of 0.25% of potassium persulfate and 0.025% of sodium anthraquinone-B-sulfonate was added to the mixture as a polymerization catalyst. Polymerization was continued to a predetermined conversion.  
 Chloroprene -100 (parts) Other monomer 5-0 Disproportionated rosin 4 n-Dodecylmercaptan 0.3 Fonnaldehyde-sodium naphthalene sulfonate condensation product 0.8  
 Sodium hydroxide 0.8  
 Water The reaction was stopped by the addition of an emulsion containing 0.03% of phenothiazine and 0.03% of tert-butylcatechol. Unreacted chloroprene was then eliminated at 60C. under an absolute pressure of mm. Hg. Thus, there was obtained a toluene-soluble polychloroprene latex.  
 B. Preparation of the gel polymer:  
  A polymerization mixture as follows was polymerized in a stirred, jacketed polymerization vessel to a predetermined conversion and post-treated in the similar manner as in the preparation of the sol polymer.  
 Chloroprene 98-100 (parts) Other monomer 2-0 Disproportionated rosin 3.5 n-Dodecylmercaptan 0.2-0.35 Formaldehyde-sodium naphthalene sulfonate condensation product 0.8 Sodium hydroxide 0.8 Crosslinking agent 3-7 Water 150 C. Blend of sol polymer and gel polymer:  
 Polymer blend 100 (parts) Phenyl-u-naphthylamine 1 .0 Magnesium oxide 4.0  
 Zinc oxide 5.0 2-Mercaptoimidazoline 0.35  
  The compound thus formed was extruded by means of a Koka-type flow tester and, thereby, the extrusion rate and the die swelling (ratio of the average outer diameter of the extruded product to the diameter of the extrusion die) were measured. The results were summarized in Table 1.  
  The test conditions by the Koka-type flow tester were as follows:  
 Die l.0mmXl.0rnrn Load GQKg/cm Temperature lOC. I  
 wherein n is an integer of from 1 to 8,  
 CH C-O-(-CH CH O-) C-C=CH wherein n is an integer of from 2 to 4, divinylbenzene and diallyl phthalate, preparing said toluene-soluble sol TABLE 1&#39; E-l g a 4 S01 polymer Gel polymer:  
 crosslinking agent Monomer composition.  
 u-Dodecylmercaptan.  
 EDMA, EDMA, EDMA, EDMA, EDMA&#39;, TDMA, DEDMA, 2 0. 5 .0. 1.0. 4.0. 4.5. 5.0. 4.0.  
 CP..--- oP &#39;IEDMA, &#39;DVB, DVB, DVB, DAP,  
  5.0. 5.0. 5.0. 5.0. 1.0. OP oP.--;-.-. CP... CP... CP-.- OP.  
 Conversion 9 93... so 95..... 80&#39; crosslinking density X100 22.7. 2.4--.. 8.2-... 22.0-.. 4.2. Monomer composition OP CP... CI... CP... OP. Mooney viscosity 21.0.; 23.0........ 23.0... 22.5... 24.5... 21.0.  
  ML1+4 (100&#34; c.)- Gill poymter/sol polymer 54/40...- 52/48.... 51/49...- 54 40-... 53/47---- 54/40.... 52/48 54/40 50/50.. 50/50.- 50/50.. 50/50. on ra 1o. v Mooney viscosity of blend 48.5..... 49.5..... 51.5--. 50.5-...- 51.5--.-- 49.0...-. 48.5 51.0 49.0-.- 50.5--. 48.5-.. 51.0.  
  ML|+4 (100 c. Compound:  
 Eiztriliggpn rate, cc./see. 28.2... 39.8- 37.1&#34;... 31.4&#34;..- 37.5..... 35.3..... 36.1 35.4 20.0-.. 27.0-.. 28.9-.. 24.5.  
  x Die swelling 1.27... 1.07 1.05. 1.20...&#34; 1.26&#34;... 3&#34;... 1.12 1.18 1.60... 1.35... 1.10... 1.52. Surface smoothness Em&#34;... Exc..... Exc-.... Exc--... Exc.. Exc..... Exc Exc Good. Exc-.. Exp-.. Exc.  
 N es; polymer by polymerizing chloroprene or a mixture of chloroprene with a small amount of at least one copoly- I I merizable monomer, and blending said toluene- BXE} ggig gf &#39;figfifi insoluble gel polymer and said toluene-soluble sol poly- ED Ethylene glycol dimethacrylate 3 5 mer, the improvement comprising polymerizing said Egg gqza y s fiq fi &#39;i i y toluene-insoluble gel polymer to a cross-linking density I ac TEDMA; 51.2 ;isfie gi cfimeoiicifim of at least 2.4 X 10 6 and a monomer conversion of at CP: Chloroprene least 80%. gf gggifg 2. The process of claim 1 wherein the cross-linking As evident from the Table l, polychloroprene elastomers prepared using a gel polymer having a density of crosslinking of at least 2.4 X 10 are extrudable at high extrusion rates without difficulty. The extruded product is characterized by a smooth surface. The elastomer prepared using a gel polymer of a crosslinking density of 0.6 X 10, which is outside the scope of the present invention, has poor extrusion characteristics.  
 What is claimed is:  
  1. In a process for preparing a polychloroprene elastomer consisting of a blend of from to 80 parts by weight of (a) a toluene-insoluble gel polymer and from 80 to 20 parts by weight of (b) a toluene-soluble sol polymer comprising preparing said toluene-insoluble gel polymer by polymerizing chloroprene or a mixture of chloroprene with a small amount of at least one copolymerizable monomer in the presence of a crosslinking agent selected from the group consisting of a compound represented by the following formula:  
 agent is ethylene glycol dimethacrylate, tetramethylene glycol dimethacrylate, diethylene glycol dimethacrylate or tetraethylene glycol dimethacrylate.  
  3. The process of claim 1 wherein the monomer copolymerizable with chloroprene is a monomer selected from the group consisting of styrene, vinyltoluene, butadiene, isoprene, 2,3-dichlorobutadiene-l,3, methyl vinyl ketone, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate and acrylonitrile.  
  4. The process of claim 1 wherein the monomer copolymerizable with chloroprene is styrene.  
  5. The process of claim 1 wherein the monomer copolymerizable with chloroprene is 2,3- dichlorobutadiene- 1 ,3.  
  6. The process of claim 1 wherein the weight ratio of said gel polymer to said sol polymer varies from 50:50 to 54:46.  
 7. The process of claim 1 wherein the Mooney viscos- 8. In a process for preparing a polychloroprene elastomer consisting of a blend of from 20 to parts by weight of (a) a toluene-insoluble gel polymer and from 80 to 20 parts by weight of (b) a toluene-soluble sol polymer comprising preparing said toluene-insoluble 65 gel polymer by polymerizing chloroprene or a mixture of chloroprene with a small amount of at least one coity (ML.., at C. of the blend varies from 30 to- 7 8 polymerizable monomer in the presence of a cross,- ge p lym r y polym rizing hloroprene Or a mixture linking agent selected from the group consisting f a of chloroprene with a small amount of at least one cocompound represented by the following formula; polymerizable monomer in the presence of a crosslinking agent selected from the group consisting of a CH CH 5 compound represented by the following formula:  
  3 3 I I CH C C O-(-CH O (&#34;I C =CH 3 3 o r i on c c-o CH CH 0 clz c CH wherein n is an integer of from 1 to 8, divinylbenzene O O and diallyl phthalate, preparing said toluene-soluble sol Polymer by pqlymeriling chloroprene or a mixture of wherein n is an integer of from 2 to 4, divinylbenzene chiofoprene with a small Copoiy&#39; 5 and diallyl phthalate, preparing said toluene-soluble sol fnenzabie monomer blending Said toluene polymer by polymerizing chloroprene or a mixture of insoiiibie gel polymer and Said toiuene&#39;soiubie Soi poiy&#39; chloroprene with a small amount of at least one copolythe improvement comprising polymerizing Siiid merizable monomer, and blending said toluenetoluene-insoluble gel polymer to a cross-linking density insoluble g e1 p 01y m e r and Said toluene soluble Sol poly 2O of at least 2.4 X 10 and a monomer conversion of at met, the Improvements compnsmg polymenzmg Sald least toluene-insoluble gel polymer to a cross-linking density 9. In a process for preparing a polychloroprene elasi of at least 2.4 X 10 and a monomer conversion of at tomer consisting of a blend of from to 80 parts by least 80% weight of (a) a toluene-insoluble gel polymer and from 80 to 20 parts by weight of (b) a toluene-soluble sol polymer comprising preparing said toluene-insoluble