Stabilization of vinyl resin foam systems
United States Patent Huntzinger et al.  
 Filed: Aug. 8, I973 Appl. No.: 386,613  
 Related US. Application Data Continuation-impart of Set. No. 149,325. June 2, 1971, Pat. No. 3.824.204.  
 US. Cl 260/2.5 P; 260/23 AR; 260/3l.8 R; 260/33.6 UA; 260/33.8 UA; 260/45.7 R; 260/78.5 E; 260/89.5 A; 260/899 Int. Cl. C08f 47/10 Field of Search 260/2.5 P  
 References Cited UNlTED STATES PATENTS 12/1968 Soltys 260/ .5 P 7/1969 Wluka 260 ...5 P 2/1973 Huntzingcr et al 260/ .5 P  
 [ Apr. 22, 1975 OTHER PUBLICATIONS Monomeric Acrylic Esters, Edward H. Riddle. Rohn and Haas Co.. Rheinhold Pub. Corp., 1954, N.Y., pp. 56-58.  
 Primary Examiner-Morton Foelak Attorney, Agent, or FirmHarold A. Hormann; Barry Moyermann [57] ABSTRACT Vinyl resin foam products having desirable characteristics including fine uniform cellular structure and low density are prepared with extended processing latitude from a foamable precursor composition which includes as stabilizing agent an effective amount of a composition comprising the reaction product, having an intrinsic viscosity, [1;], in deciliters per gram, determined in chloroform at 30C., of less than about 0.35 of the polymerization of the monomeric esters of methacrylic acid and alcohols having from 3 to 5 carbon atoms. effected in the presence of chain transfer agents.  
 6 Claims, No Drawings STABILIZATION OF VINYL RESIN FOAM SYSTEMS This is a division of application Ser. No. I49,325. filed June 2, 1971. now US. Pat. No. 3.824.204.  
 BACKGROUND OF THE INVENTION 1. Field of the Invention This invention concerns the stabilization of vinyl resin foam systems to provide cellular or porous resinous bodies.  
 2. Prior Art Vinyl plastics of the type generally known as polyvinyl chloride or PVC constitute a large segment of the plastics art. The preparation and use of foamed polyvinyl chloride falls within a fairly narrow area of the vinyl plastics art. Typical general prior art appears in such US. Pat. Nos. as 2,056,796. 2,960,728: 3.093.525. 3,050,4l2; 3,063,110. 3,197,472; 3,267,197; 3,270,032; and 3,284,545. More closely related are U.S. Pat. Nos. 3,399,107 and 3,417,038 of which 3,399,l07 concerns the use of homopolymeric methacrylate esters in relatively high concentrations in the preparation of certain cellular polyvinyl chloride products.  
  The present invention brings to the art an effective and economical stabilizing agent capable of providing foamed polyvinyl chloride and polyvinyl chloride products not only with improvements in their formation but also with improvements in the product such as have been previously unattainable with the ease and consistency now made possible.  
 SUMMARY OF THE INVENTION This invention concerns the stabilization of polyvinyl chloride plastic compositions. having foamed cellular structures during their formation and transformation to final form. The precursor plastic compositions comprise a vinyl resin and a plasticizing agent. Provision for the creation of the foam or cellular structure is generally made by inclusion in the precursor composition of a blowing agent which may, however, be reduced in amount or eliminated entirely by mechanical, i.e.. froth, technique in creation of the foamed or cellular structure. Stabilization of the foam, along with other improvements described herein below, is obtained when there is present with the precursor materials during the foaming and fusion step or steps an amount in the range of 0.05 to 2.0 part by weight based on the polymeric material as herein defined per 100 parts by weight of fusible resin in the formulation a polymeric material having an intrinsic viscosity [1)] at 30 CHCIg; in the range of 0.05 to 0.35 and obtained as the reaction product of the polymerization of one or more of the monomeric methacrylate esters of C to C alcohols with a chain transfer agent and a polymerization initiator all dissolved in a suitable solvent.  
  The intrinsic viscosity, [1 in deciliters per gram is defined in the Polymer Handbook, 1. Brandrup &amp; E. H. lmmergut, lnterscience Publishers, New York, 2nd Printing, 1966, pp N 1,2. The molecular weight of a polymer is related to its intrinsic viscosity by the equation:  
 [n] kM in which M is the molecular weight, k and a are con stants, and a is between 0.5 and 1. Thus the higher the intrinsic viscosity of a polymer, the higher the molecular weight.  
  The polymeric material stabilizer additive of this invention may be prepared by any method whereby a preponderant amount of the monomeric methacrylate and a minor amount of chain transfer agent react to form polymeric product having an intrinsic viscosity [n] at 30 CHCL; in the range of 0.05 to 0.35 upon suitable polymerization initiation and at acceptable polymerization conditions. Such polymeric material may be recovered in substantially pure form from the polymerization system by known means which include precipitation of the polymer with a nonsolvent, solvent evaporation, filtration or the like. Preferably however the reaction product is obtained at conditions and in such systems such that the entire solution is recovered and employed as recovered and used in amounts providing the polymeric material in the above-defined range.  
  The monomeric C to C methacrylates are appreciably more suited to the preparation of the polymeric materials than the methacrylate esters of the ethyl or lower alcohols or of the hexyl or higher alcohols. The normal butyl methacrylate and the isobutyl methacrylates are particularly desirable.  
  The chain transfer agents include the known chain transfer agents such as mercaptans, halo compounds such as carbon tetrabromide or carbon tetrachloride. compounds with allylic hydrogen, or the like which act in known manner in the noninterference with the kinetic chain which acts with the aid of the transfer reac tion to produce several polymer chains. While it is not surprising that the chain transfer agent usage here has the result under the appropriate conditions of providing the polymeric material product in the relatively shorter polymer chain lengths as indicated by the lower values of intrinsic viscosity. it was discovered that the polymeric materials thus obtained are surprisingly more effective than the high molecular weight homopolymers derived from similar monomeric methacrylates in some somewhat related use systems and distinctively different in other systems not too otherwise dissimilar.  
  A particularly surprising result was discovered in finding that certain compounds having vinylic H, particularly dibutyl maleate and dibutyl fumarate, are par ticularly effective in the role of transfer agents in giving an effective polymeric material of excellent stabilizing nature either as the polymeric material itself or more particularly when the entire polymerization system is such as to permit its use in its entirety as recovered.  
 It is. therefore, among the objects of this invention to a. to provide a polyvinyl resin foamed product of desirable nature including fine pore structure, with the pores uniformly sized and distributed throughout the structure;  
  b. to provide increased tolerance in the ability of emulsion grade plastic resin to accommodate extender (suspension) grade resin and still produce quality product;  
  c. to provide greater processing latitude in times and temperatures in the preparation of products, particularly at unusually high fusion temperatures previously considered detrimental to the production of quality product;  
  d. to increase the capacity of precursor formulations for higher filler loading and for greater pigmentation:  
  e. to provide precursor formulations amenable to ready processing by injection molding and by calendering; and  
  f. to provide enhanced manipulative techniques through utilization of properties associated with and in accordance with the products and processes of the invention. These and other related objects will be apparent from the detailed description and examples which follow. While the following material describes a preferred mode of operation and various typical embodiments. it is understood that the presentation is of an in structive and illustrative nature.  
 DETAILED DESCRlPTlON OF THE INVENTION As noted above the chain transfer controlled polymerization of the C -C methacrylate may be effected in any appropriate manner. The practical system is typically one involving a solvent characterized in its ability to dissolve the precursors and product and is employed in an amount ranging from the minimum required for such solvation to a maximum limited. more for practical reasons than for effect on the reaction. to about 2 times by weight of the weight of the C -C methacrylate involved. Such solvent is further required to be nonreactive in the precursor composition in the absence of a suitable polymerization initiator although the solvent may be reactive in the presence of an initiator and may of itself have chain transfer properties. Such a solvent must be compatible with all of the ingredients as well as with the end use systems when its presence is retained in part or in toto in the polyvinyl chloride foam stabilization. Such solvents. therefore. include mineral spirits. benzene. toluene. xylenes. carbon tetrachloride, chloroform, bis-(2-ethylhexyl)-phthalate. and related materials known and/or determined as suitable.  
  The polymerization reaction requires the use of an initiator to start the chain formation. Such initiator may be any of the free radical type. of which the various peroxides are embodiments. Benzoyl peroxide is one such suitable initiator. The initiator use requires a measure of care in that it is known excessive amounts may lead to undesirable and possibly violent reactions. Also to be noted is that chain length and thus molecular weight of the polymeric product is sensitive. in addition to the polymerization temperature and the amount and type of chain transfer agent. to the amount of initiator employed and that the chain length decreases inversely with regard to the amount ofinitiator in the system. To all practical purposes therefore to obtain proper reaction initiation. polymer chain length within the prescribed range and for suitable reaction control the initiator usage level is within the range of 0.l to 5.0% by weight of the weight of the C -C methacrylate in the polymerization system exclusive of other ingredients such as the solvent.  
  Thus. typical polymerization precursor systems have 30-50% of the C -C methacrylate monomer. 0.2-5.071 initiator. chain transfer agent of at least 0571 and up to when the chain transfer agent and the solvent are different and the solvent is not a chain transfer agent and up to about 69% when the solvent is a chain transfer agent.  
  Of the various methods for the polymerization reaction an unsophisticated method is to have all the ingredients in a reaction zone in an inert atmosphere. e.g.. nitrogen. and to effect the reaction by heating the contents at a temperature in the range of -l00C. for a time period in the range of about 3 to 8 hours at about atmospheric pressure with continuous agitation. Exclusive of the above-noted effect of the initiator on molecular weight. the molecular weight tends to be lower at higher temperature.  
  Another somewhat more sophisticated but fundamentally similar system involves charging the reactor vessel with a portion of the solvent and the monomer with or without a portion of the initiator and/or chain transfer agent or neither and under a nitrogen cover heating to a temperature of 70-l00C. with stirring. To the reaction zone there is then added simultaneously at a more or less uniform rate over a period of 2 to 8 hours a first solution comprising a mixture comprising the balance of the monomer and transfer agent; and a second solution comprising the balance of the solvent and initiator. For uniformity of product it may be found desirable to maintain the reactant mass at the elevated temperature with continued stirring for an additional period such as 30 to minutes after all of the ingredients have been combined.  
  Consideration of the following examples will aid in an understanding of procedures and advantages available in accordance with this invention.  
 EXAMPLE I A polymeric composition was prepared from a system comprising isobutyl methacrylate and dibutyl maleate. The preparation was as follows: To a glass lined vessel was charged 4.6 parts by weight lsobutyl methacrylate 6.9 parts by weight Dibutyl maleate 1 L5 parts by weight Mineral spirits 0.06 parts by weight Dihenzoyl peroxide Solution No. l Solution No. 2  
 Parts by Weight Parts by Weight lsohutyl methacrylate 691 Dlbutyl maleate 4.6 Mineral spirits 4.6 69.0 Dihenloyl peroxide 0.6  
 The polymerization reaction was continued by maintaining the contents of the vessel at 90C. for 30 minutes after all solutions were charged to the vessel.  
  The contents of the vessel were then cooled to about room temperature and recovered. The recovered material was a colorless liquid with a Brookfield Viscosity at room temperature of 650 cps. The NMR spectrographic examination of the product indicated that somewhat more than 95% of the isobutyl methacrylate had polymerized (showed less than 5% isobutyl methacrylate of the original charge); also. that somewhat less than 5% of the original dibutyl maleate was no longer present as the free maleate.  
  A portion of the product was treated with methanol to precipitate the polymeric material which was separated and recovered. This recovered material was purified by dissolving in acetone. treated with water to again precipitate the polymeric material. and the precipitate was separated and dried. From the dried sample a portion was dissolved in CHCL, and the intrinsic viscosity [1 was determined at 30C. as being 0.247. The weight average molecular weight was 55.000 and the number average molecular weight was 30.000 as determined by gel permeation chromatography. The NMR and IR spectra were similar to those of homopolymeric isobutyl methacrylate, being unable to distinn guish. the structural difference in the overwhelming or smothering situation of the predominantly methacrylate polymer structure.  
 A formulation was prepared using the following:  
  This plastisol formulation was employed in foam formation without cell stabilizer additive and with varying amounts of the cell stabilizer product prepared as described above The several samples without and with added cell stabilizer were spread as a mil coating on release paper and fused and expanded for 1 /2 minutes at 460F Product of the material without the cell stabilizer had a rough surface and had approximately cells per linear inch. a condition unsatisfactory and an acceptable as suitable foam product which generally requires a cell count per linear inch of at least 120. The product of the material containing the cell stabilizer added on the basis of the solids concentration in the recovered product of amounts of 0.2, 0.4. 1.0 and 2.0 parts per 100 parts of the resin had smooth surfaces and cell counts in every case above 170 cells per linear inch. The foam product of the plastisol containing the cell stabilizer had excellent physical and mechanical properties including foam densities in the order of 20 lb/cu.ft.  
  In the same formulation polymeric products prepared from isobutyl methacrylate having intrinsic vis cosities of 0.56 and 1.13 respectively. when formulated and fused in like manner at like concentrations. gave products of generally poor and unacceptable quality in both surface characteristics and low cell counts.  
 EXAMPLE 11 A readily foamable recipe was prepared to illustrate the improvement obtainable in resistance to overblowing.  
 Parts by Weight Marvinol 53 (paste PVC resin) Escambia 8200 (extender PVC resin) 40 DlOP (di-isooctyl phthalate) 60 BB? (butyl benlyl phthalate) 10 Paraplex G-oZ (epoxidized soybean oil) 5 Athastab ABC -1 (liquid zinc activator) 2 Atomite (calcium carbonate) Azodicarbonamide (blowing agent) 1n the absence of added cell stabilizer this material when fused at 460F. for 3 /2 minutes resulted in a collapsed foam system having rough and irregular distribution of the pores of 30-50 per linear inch. However. when the cell stabilizer of Example 1 was added to the above formulation in amounts ranging from 0.1 to 1.5 parts by weight based on the weight of contained solids per parts by weight of the resin. the products had excellent and uniform pore sizes and distributions ranging in the order 200 cells per linear inch and densities in the ranges of 18 to 20 lb/cu.ft. In similar runs where the cell stabilizer product of Example 1 was diluted with added mineral spirits to a level of contained solids of 25% by weight. equally good results were obtained when used in the formulation in the same range of concentration based on weight of contained solids.  
  A further advantage resides in the use of the cell stabilizer with similar formulations employed in the production of foam covered fabrics which are prepared by first coating the fabric with plastisol. causing the plasti sol to foam and fuse and then in a second operation further subjecting the thus coated fabric to heat embossing. Here. the use of the cell stabilizer additive in amounts such as in the order of 0.1 to 0.5 parts by weight per 100 parts of resin reduces to a considerable extent the temperature critic-ality heretofore normally existing in the prevention of foam collapse during the heat embossing period. The practical temperature range would thus be extended from a range of about 10F. to a broader range of about 50F. or greater.  
  1n the same formulation the effectiveness of the cell stabilizer as prepared in Example 1 on the foam stabilization efficiency over extended time periods is shown in Table 1 below.  
 Table l Cells/inch Foamed at 460F.  
  2 mins. 3 mins. 4 mins. No Stabilizer 205 95 40 Stabilizer of this invention 0.05 phr 210 I40 (1.1 phr 200 I71) 151) EXAMPLE Ill coating on release paper and foaming and fusing for 2 minutes at 440F.  
  The above table shows the presence of the cell stabilizer has a highly beneficial effect at high level usage of extender resin in the formulation.  
 EXAMPLE IV A formulation was prepared as follows:  
 EXAMPLE IV A formulation was prepared as follows:  
 (icon I24 (Paste P\&#39;C Resin) 60 Escambia X200 (Extender PVC Resin) 40 DOP (di-(2-ethyl-hexyl) phthalate) X Dythal (dibasic lead phthalate) 3 Calcium carbonate as shown Azodicarbonamide 2 Cell stabili/cr as shown Various amounts of calcium carbonate filler were employed and sample systems without and with the cell stabilizer are shown in Table 3 below.  
 Table 3 Cell stabilizer Calcium Carbonate of Example l Foam Quality phr phr cells/inch U 0.5 I70 0 50 0.5 I70 (l 4U 40 0.5 H10 (it) ll 30 on 0.5 140 The above data show that the use of as little as 20 parts per 100 parts by weight of resin of calcium carbonate filler in the absence of the cell stabilizer results in foam collapse to an unacceptable product. On the other hand with cell stabilizer present acceptable product is obtained when as high as 60 parts by weight per 100 parts by weight of resin of calcium carbonate filler are present.  
 EXAMPLE V In the preparation of colored products comprising polyvinyl chloride. the matter of pigmentation is extremely important to the producer. As shown below the use of the cell stabilizer in this invention substantially enhances the ability of polyvinyl chloride systems to tolerate a high order of pigment additive and thereby obtain a desirable richer coloration. A formulation was prepared as follows:  
 Marvinol 53 (dispersion resin) Marvinol l-l (blending resin) 30 DOP 20 DlDP (diisodecyl phthalate) l8 Monoplcx NODA (n-octyl ndecyl adipate) 9 Admix 7l 1 (epoxidized oil) 5 \anstay 8300 (Pb stabilizer) L9 Ferro 5078 (Pb stabilizer) Atomite (calcium carbonate) l5 Azodicarbonamide l .8 Carbon black pigment as shown Foam stabilizer as shown The samples were prepared as cast films and foamed and fused for 4 minutes at 420F. Comparative data are shown in Table 4. These data show that quality foam product was obtained at carbon black pigmentation loading levels twice as great by the use of the cell stabi&#39; lizer as in the absence thereof.  
 Table 4 Carbon Black Pigment Foam Stabilizer (Bone Black) of Example I Foam Quality &#39;0 100 (polymer basis) cells/inch phr  0 0 I60 0 0.2 H10 5 0 I55 A 5 0.2 I55 7 0 7 0.2 150 l() l) 35 l() 0.1 l-lll EXAMPLE Vl \&#39;C PM (Injection molding grade of PVC) )00 DOP (bis-t Z-cthylhexyl )-phthalate) 73 Paraplcx C1412 (epoxidized oil) it Actafoam R-3 (commercial heat stabilizer and blowing agent activator) Stearic acid 0.15 Atomite (calcium carbonate) 8 Azodicarbonamide (blowing agent) 0.75 Foam Stabilizer (of Example I) as shown The above formulations in the various lots as indicated below were separately mixed in a Hobart mixer at low speeds for approximately l0 minutes. Each mixture was fluxed on a 2 roll mill at roll temperatures in the order of 2703()0F. for 7 minutes. The milled product was sheeted off at 0.25 inch thickness. A suitable mold and unattached cover plate was preheated in a steam heated press at 360F. for at least 15 minutes and then filled with the cut strip having dimensions of approximately 4 X l inch. The cover plate was applied and fastened. Pressure in the press was adjusted at 5000 psig and the mold was maintained at about 360F. and 5000 psig for 6 minutes. Pressure was released to allow for expansion of the stock and cooling by means of a water flow was effected simultaneously. After approximately 2 minutes the mold assembly was removed from the Table 5 Cell Stabilizer Foam Quality l of Example I (phr) cells/inch Blow ratio l l I Ratio of final foam thickness to unblown stock thickness EXAMPLE Vll Calendered foam products likewise can be improved when the cell stabilizer of this invention is employed. A recipe was prepared as follows:  
 \t&#39;ygen I I0 (calendering grade of PVC) I00 DlOP (diisooctyl phthalate) 80 Nuostabe \&#39;-l026 (Pb stabilizer) 2 Stearic acid 0.4 Alodicarbonamidc (blowing agent) 5 Foam Stabilizer as shown Table 6 l Minimum Etl&#39;ective Concentration Foam Stabilizer According to US. 3.270.032 Of Example I l Quantity of foam stabili/er needed to produce a foam ha\ing a cell count of II to I50 cells/inch. In the absence ol&#39;cell sta ili/er cell counts are in the to cells/inch range.  
 EXAMPLE Vlll In a manipulative manner identical with that shown the preparation of the cell stabilizer material of Example 1. reaction vessel was charged with lsobutyl methacrylate 4.6 parts by weight Dibutyl fumarate 6.9 parts by weight Mineral spirits I I5 parts by weight Dibenyoyl peroxide 006 part by weight n-Dodeeyl mercaptan 006 part by weight To this was added the 2 separate solutions. one composed of 69 parts by weight of mineral spirits and 0.6 part by weight of dibcnzoyl peroxide: and the second solution composed of 69.] parts by weight 4.6 parts by weight 4.6 parts by weight 06 part by weight lsobutyl methacrylate Dibutyl fumarate Mineral spirits n-Dodecyl mercaptan The product recovered from this reaction. except for a mild but noticeably different odor. had physical and chemical properties similar to the cell stabilizer product of Example I. When employed as cell stabilizer in like amounts in identical formulations the stabilizing activity in all instances was at least as effective as the demonstrated effectiveness of the cell stabilizer of Example l.  
 EXAMPLE lX The procedure of Example I was followed in the preparation of cell stabilizer except that normal butyl methacrylate was substituted for isobutyl methacrylate. The polymeric material in the product had an intrinsic viscosity of 0.23 and was approximately similar in its cell stabilizing and other beneficial aspects to that of the product of the polymerization reaction in Example EXAMPLE X In a polymerization run similar to that in Example l except that dilauroyl peroxide was used as initiator and no chain transfer agent was employed. the polymer after polymerization reaction at C. had an intrinsic viscosity of above 0.4 and the recovered product was generally ineffective as a cell stabilizer in the formulation of Example I.  
 EXAMPLE Xl Following the procedure of Example I similar ingredients were employed in the same amounts with the exception that xylene was substituted for the mineral spirits. and the chain transfer agent was changed from dibutyl maleate to 0.7 parts by weight of dodecyl mercaptan. Xylene does exhibit some chain transfer properties. The isolated polymer from the recovered product has an intrinsic viscosity. [1)]. of about 0.31. The total product composition in tests of its cell stabilizing effectiveness showed an effective minimum concentration to produce a cell count above 120 cells per linear inch in the plastisol formulation of Example I to be in the order of 0.6 part by weight per parts of resin.  
 EXAMPLES Xll. Xlll AND XlV The halogen compound used in Example Xll was dis solved in the monomer. while that used in Examples XIII and XlV was added to a 500 mil reaction flask. A volume of solvent equal to that of the monomer and halogen compound dissolved therein was used to dissolve the peroxide. and the remainder of the solvent was placed in the reaction flask. The monomer and solvent solution were then added simultaneously at constant rates over 6 hours to the stirred flask. the contents of which were maintained under nitrogen at 80C. throughout the addition period. and for V2 hour longer. The solutions were then cooled.  
  The materials recovered from the several reactions had polymeric products. as measured, on separated polymer solids, with intrinsic viscosity values of less than 0.3. The recovered products. unseparated. employed as cell stabilizers in the plastisol formulation of Example I. each exhibited an effective minimum concentration to obtain cell structured product of above 120 cells per linear inch in the range of 0.4 to 0.5 part by weight per 100 parts by weight of resin.  
 EXAMPLE XV Two separate batch polymerization reactions were run. each employing 14.2 parts by weight of isobutyl methacrylate dissolved in 30 parts by weight benzene and differing in that one contained 0.2 part by weight dibenzoyl peroxide and 0.1 part by weight of n-dodecyl mercaptan and the other contained 0.l part by weight of dibenzoyl peroxide. Each batch was stirred at reflux conditions under nitrogen atmosphere for 4 hours. The polymeric material in the product from the batch containing the mercaptan had an intrinsic viscosity of 0. l 7. The product from the batch containing no mercaptan but also considerably larger than normal amount of initiator had an intrinsic viscosity of 0.30. indicative of the possibility of obtaining relatively low molecular weight product in a system with the chain length shortening effect of a relatively large amount of initiator. in tests on cell stabilizing activity, the sample prepared with the mercaptan showed an appreciably higher foam stabilizing activity than the higher molecular weight material prepared in the absence of mercaptan. The minimum effective concentration to obtain foamed product from the resin formulation of Example I to produce a cell structure above 120 cells per linear inch was 0.3 for the material prepared with mercaptan as opposed to 0.7 part by weight per l parts of resin of product prepared in the absence of mercaptan.  
  The foregoing description has concerned polyvinyl chloride resins and resinous compositions as embodiments of the materials favorably responsive to the stabilizing effect of the stabilizers of the invention. It is to be understood that such descriptive terminology includes those copolymers which are derived from predominantly vinyl chloride with minor amounts of copolymerizable comonomers. For instance the cell stabilizer material of this invention is very effective in stabilizing the relatively low-temperature fused foam carpet backing derived from copolymers of polyvinyl chloride and polyvinyl acetate.  
  Other tests have demonstrated that the cell stabilizer of the invention provides a marked advance in processing and preparation of quality cellular products where abnormally high processing temperatures are encountered or desired. This feature is highly desirable in that oven residence time can be reduced substantially with a resultant increase of production rate. It has been found that with the cell stabilizer of the invention temperatures as high as 535F. are feasible for times up to 0.7 minutes and that temperatures up to 550F. are possible for times as long as 0.5 minutes.  
  Obviously. many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.  
 What is claimed is:  
  l. In the process of foaming a vinyl chloride resin plastisol containing a chemically heat decomposable blowing agent the improvement which comprises adding to said plastisol composition a cell stabilizer liquid, on the basis of contained dissolved solids. in an amount in the range of 0.05 to 2.0 parts by weight per parts by weight of fusible vinyl chloride resin. said stabilizer consisting of the total product of the reaction. at polymerization conditions. of a precursor composition of at least one monomeric methacrylate ester of methacrylic acid with a C to C alcohol; a chain transfer agent selected from the group consisting of dibutyl maleate and dibutyl fumarate; an initiator; and solvent. said solvent being present in an amount at least sufficient for solvation of precursors and product to an amount equal to and no greater than 2 times the weight of monomeric methacrylate ester. and said solvent being non-reactive in the precursor composition. in the absence of said initiator. wherein said precursor composition consists of 0.1 to 20 parts by weight of chain transfer agent and 0.05 to 2.0 parts by weight of initiator per 100 parts by weight of the monomer methacrylate ester. and wherein the separable polymeric material produced from said total product of reaction has an intrinsic viscosity. measured at 30C. in CHCl in the range of 0.05 to 0.35 deciliters per gram.  
  2. The preparation of foamed cellular bodies in accordance with claim 1 wherein said stabilizer solution is the reaction product of a precursor composition consisting of isobutyl methacrylate as the methacrylate ester. dibutyl maleate as the chain transfer agent. dibenzoyl peroxide as the initiator, and mineral spirits as the solvent.  
  3. The preparation of foamed cellular bodies in accordance with claim 2 wherein said precursor composition consists of 100 parts by weight of isobutyl methacrylate. 1.0 to 60 parts by weight of dibutyl maleate. 0.4 to 10.0 parts by weight of dibenzoyl peroxide. and from 100 to 200 parts by weight of mineral spirits.  
  4. The preparation of foamed cellular bodies in ac cordance with claim 3 wherein said precursor composition consists of 100 parts by weight of isobutyl methacrylate. 15.6 parts by weight of dibutyl maleate. 9.0 parts by weight of dibenzoyl peroxide and 102 parts by weight of mineral spirits.  
  5. The preparation of foamed cellular bodies in accordance with claim 1 wherein said elevated temperature is above about 500F.  
  6. The preparation of foamed cellular bodies in accordance with claim 1 wherein said precursor composition comprises a fusible vinyl chloride resin comprising a major amount of extender resin. and fusion is effected at a temperature of up to 550F. for a time no greater than 30 seconds.