US2576722A - Chloro-anacardic polymers and methods of making the same - Google Patents

Description

Patented Nov. 27, 1951 OF FI'CE CHLOROI-ANAGARDIC POLYMERS AND. METHODSLOF. MAKING THE SAME:-

Emil" ES Novotny', ,Pro spectvill; and George K; Vogelsang; Cheltenham, Pa, assignors to' 'Tlie Bordeni-Compan-y; New York,-N.-1.Y., art-corpora tlomof: New-Jersey No Drawing. Application lime 16;.1949", Serial No. 99,576

9:Claima;-. (01. 260-46) This invention relates to ch1oro=anacardie polymers and to methods for making the-same: The present application is a continuation irrpart of application SerialNo.- 486,432; fi1ed'-May"10 1943 (now abandoned); Said application is a 5 continuation in part of application Seri-al'=No.- 227,528; filed August30, 1938 (now-abandoned); which is in turn'a continuation in part of appli cation-Serial No. 188,796; filed February 4, 19385 Said last mentioned application matured into -l0 Patent 'No. 2,306j077 on December 22 1942;

By way-of introduction, itmay be-stated that when' chlorinating' anacardic material-according to the teachings of the above identified patent and patent applications,- particularly when the"- chlorination is "carried out at elevated temper atures in the absence of I a diluent ormodifyingagent; a small but'nevertheless noticeableamount of condensation-polymerization occurs-during. the

process-of chlorination. The condensation p'oly merization; which may occur during the'process o1 chlorination; isgenerally-not suclraato a preciably alter the characterof" the ultimate chlorination product whichlis essentially monomeric in character. Nor is it possible to substan- 26 tiallyincrease-theamount of condensation-polymerization that can occur during the process of chlorination because-as thecondensation' poly merizationprogresses the viscosity of the mass soon reaches a-point which renders it d-iiiioirlt; 30

not impossible,- to introduce further desirable-- amounts of chlorine. If a solvent or diluent' is used for the purposeof lowering the viscosity;

the -chlorination proceeds further,- but '-'the* reac= tion-- ofc0ndensation-polymerization is slowed down'to-a negligible degree.-- It'will thus be seen that intheprocess-of chlorination "there-aresel-f limiting factors restricting the amount of con--- densation-pol-ymerization to a'loW value-.

, Applicants have now'found it'possible tech- 40 taina degree of 'condensanon-polymerization, far beyond the maximum normallyobtainable;- dur-i-ng the process-of chlorination per se: Fur thermore, they have found that the degree or;

c0ndensation-polymerization can readily b'e con' process of-condensanon-polymerization entails -a'-- building up of the molecular weight of the material, the mean molecular "weight ofthe-product' can be conveniently cited as a'- criterion' of the degree oi condensation polymerizatlom- Briefly stated, the -method= of the-invention" consists 'subje'ct-ing-- substantially monomeric chlorinatedanacardic material having achlorine contentof-"at least-10% on the weightbf thez anacardic material to a heat treatment with or without one or more co-reactants until the-mean molecu-lar' weight has at least doubled; The? chloro-anacardic=material is referred toas being: "substantially monomeric," becausewhateveriincidental condensation-polymerization; it any, thatmay have occurred during the process) of chlorination is tooinsignificantto materially alter the character of the chloro'-anacardic: ma terial, which still" has all the attributes'associated with monomeric anacardic material.

The starting materials for practicing-the res! entinvention are the substantially monomeric: chlorinated anacardicmaterialsdisclosed in Patent No; 2,306,077 above mentioned and in appli-- cation Serial No: 458,950 filed September 19,1942: (now abandoned) the primary object/of theair'i' vention being to increase greatly the number of: useful derivatives of anacardic materials; andto extend" their field of utility.

Another very important object is to provide a: largenumberof compounds and compositionshaving characteristic and unique proper-ties which render'them particularly suitable for many special usessuch as synthetic resins andrubber-spplasticizers; co-reactants; etc.

Other'objectsof importance-will appear or: will'be pointed'out as the description'proceedst The substantially monomeric chlorinated-anacardic starting materials maybe made in-"various ways: For instance, anacardic material may--'be-= subjected "to theaction of a chlorinating agent under'suitably controlledreaction conditions=un-= tilthe anacardic' material has taken up between-' 10% and 30 of chlorine, based upon the weight 4 of the anacardic-material. The-chlorinating*' agent 'mayadvantageously be-gaseous-chlorine; which case the gas ispassed into the anacard-ic" material:

A- particularly suitable way oi" making the" starting materials is to mix anacardicmaterials with anon anacardicmaterial,"and tochlorin'ate constitute at "least' 50 =of the mixtureol *ana cardic' anctnon-anacardic materials the presently preferred' embodim'ent ofthe is invention, the non-anacardic material is selected from the group consisting of vegetable and animal oils and fats and their fatty acids.

The chlorinated starting materials .are subjected to a treatment or processing toraise their molecular weights and intrinsic viscosity. This treatment or processing may involve the use of yield a dense, compact material. 1-

The product of the foregoing procedure may be .blended with any one or more of a variety of heat or reaction with any one ormore of a wide variety of powerful reactants or a combination of reactants and heat. A permissible variation is first to heat the chlorinated anacardic materials and then to react the heat-treated material The following examples are illustrative of the with appropriate co-reagents, preferably with heat.

The principal purpose of the heat treatment is densation or reaction with the other reactants.

I to bring about the desired polymerizationjcon" Other effects are also brought about. For inmaterial as well as water which is engendered during the heat treatment. I

Another permissible variation includes the step of introducing live, preferably super-heated, steam either into the bodyof the mass or upon the surface, thereof. The steam apparently. has two functions: First, theuse of steam distilla tion results in a more ready and thorough removal of volatiles and odorous ingredients. Secondly, there is definite evidence that the steam or for that matter hot water enters into reaction with the chlorinated anacardic material resulting in a further elimination of hydrogen chloride concomitant either with the introduction of oxygen,.'e. g., OH groups into the mass undergoing the, heat treatment, or in the introduction of double bonds. v rectly attribute to the polymerization of the mass.

It should be pointed out, however, that this step of subjecting the chlorinated anacardic material under the influence of heat to the action of steam (or hot water) is entirely optional. Tests made uponthe final processed products reveal that the difierences in physical and chemical properties of materials processed with or without steam are in the nature of degree rather than of kind. However, it appears that the steamtreatment is desirable in that it yields products that are some What more stable and exhibit less tendency to give off acidic components in the ultimate articles or:

which they may be substituents. I v

Another variation consists in subjecting the chloro-anacardic material first to a heat treatment in a kettle with or without the application of reduced pressures and the action of steam, and

then to a further heat treatment, which may be.

ata higher temperature in an oven. If the timetemperature schedule is sufiiciently drastic, the

normally liquid products gel and eventually set to a spongy, porous, rubbery mass. In this latter instance large quantities of hydrogen chloride are eliminated. In such a baking operation, it has been found that a certain amount of superficial oxidation occurs. Such oxidation is ordinarily not objectionable but it can be greatlyminimized, if not altogether eliminated, by carrying out the further heat treatment in the presence of either The latter may or may not dicompounding ingredients so as to yield a fairly stable 'and neut'ral material, which lends itself very readily to further processing with substances such as butadiene-acrylonitrile rubbers or polyvinyl acetals, e. g., plasticized polyvinyl butyral.

process of the present invention:

1. Example 1 I Chlorinated anacardic material, with a chlorine content of not less than 10 per cent and preferably between 20 and 28 per cent, is heated in an oven as per the following time-temperature schedule: Slowly bring up to 220 F. Hold atthis; temperature for about one hour, then raise the perature usually raises the molecular weight toia point at which isproduced a highly viscous product just short of the gel point. ment at the elevated temperature for aperiod of approximately six to ten hours usually yields a. puffed-up spongy soft rubbery mass. It isto be noted that in this particular example no stirring or agitation is employed. This, in a sense, has

the disadvantage of yielding a somewhat ,non-

uniform product. However, formany purposes the material after blending on differential rolls (in the instance of the soft solid) yields a product of adequate uniformity.

' 7 Example 2 Chlorinated anacardic materialprepared in ac cordance with the disclosure of Patent No. 2,306,077 is placed into a glass-lined kettle provided with an agitator and facilities for heating and cooling. The mass is first gently heated, and when the product is liquid enough the agitatoris started and kept running. When the temperature attains a value of between 210 F. and 230 F'., a

very decided quantity of foam is engendered duev to the elimination of water and other ready volatiles.; In this phase of the operation the amount of heat-that can be applied to the mass is strictly limited by theamount of foam that it is permissible to engender, this latter being determined by the. free volume of the kettle. The foam, however, soon subsides andfrom that time on ever increasing amounts of heat can be applied to the reaction mass. perature of 320 F.,and if possible, to maintain a temperature no higherythan 300, F.. The 'material is conveniently kept at or above 275 F. for

having a viscosity comparable to that of heavy molasses. Such material has utility as a plasticizer for rubber as well as for a widevariety of other purposes. This material is also capable of being thermoset by a wide varietyof reagents in-- eluding hexamethylenetetramine, formaldehyde,-

a reactiveketo-aldehyde reaction products, many f the m re w r u ,.ecc l rg e s q rn t el ubse A heat treat-.

It is desirable not to exceed a temher, at. "'inepuysmartifidchemicalpfoberusoi'" the ultimate materialdependin lar'ga'measure upo'nfihe original or -ultimate "chlorine content. When it is desired to produce plasticizers, chlorinated anacardic materials withohlorine contentsofbetween '1'5 and20per cent are'preferably used. When it is desired to produce materials which, as is more fully expla'inedin a further example, are'to' be used as rubber exten'dersor" as binders in conjunction with polyvinyl butyral, chloro-anacardio materials 'with f'- chlorine contents of between '20 and30'per- 'cen't,-e. "g; 22- to 26 per cent of 'chlorinaare preferably used.

Example 3 Chlorinated ana'cardic material prepared in accordance with the disclosure of Patent No. 2,306,077 is placed into aglass'lined kettle provided with a stirrer and means'for heating. The material is slowly heated. When themass becomes sufficiently fluid the stirrer is started, and

from this time on the mass is continuously stirred. The temperatureis gradually raiseduntil the mass foams up. After the foam has subsided the heating is continued until a temperature of 240 F. or higher'is attainedpat which time vacuum is slowly applied to the kettle. The temperature is either maintained at 'theprevious level oris raised'to'between 280 Rand 335? during the *whole of which time the-vacuum is the latter instance, the stirrer mustbe'stopp'ed just prior'to the gelling. When-the reaction of condensation or polymerization has proceeded to the proper point, the vacuum is shut off and the material withdrawn from the kettle, It will be noted that in the instance where the endproductis a soft rubbery-material, carrying out of the whole of the operation-in a kettle has the disa'd vantage that the kettlemust-be dismantled in order to remove the product. For-this reason, the reaction is preferably carried out in the kettle well short of the point where the mass sets up, and the fluid product'is then withdrawn into pans which are placed in'an' oven. Itis'a relatively simple matter toremove the rubbery prodnot from such pans. Material processed with the aid of vacuum is-quite similar to that processed without vacuum, except that the material is somewhat freer of volatiles and odorousconstituents.

The products of the foregoing prooesshave molecular weights'which are very'much higher than that of the highly viscous products of Examples l and 2, indeed the molecular-weights are usually so high that they cannotbe-determined by ordinary methods.

Example 4 or superheate is b own-over the surreeefef tne mass or bubbled throughthe' inass while-maintaining the material the stated temperature'range. The processing is'continued until the desired increase in molecularweight has occurred. The fluid mass is then-withdrawn from the kettle and may, if desired,-be subjectedto further processing as describedelsewhere. Material subjected to theabove steam t'reatment is quite similar to material processedwithou'tthe' aid of steam, but is freer of objectionableodorsand haslesstendency to liberate acidic products.

Example 5 Chlorinated anacardic material prepared in accordance with the disclosure of Patent No. 2,306,077 is placed into a-glasslined kettle-provided with an agitator-and facilitiesfor vacuum and the blowing inof steam either through'the mass or on the surface of the material. The material is slowly heated. The agitatoris started-as soon as possible and kept running throughout the remainder of the operation. The heating-is continued until the material foams. After defoaming, the temperature is raised to above 220 F.," at which time a greater or lesser vacuumis applied.

The vacuum is maintained for a period thatmay' vary from fifteen minutes to a few hours. The vacuum is then discontinued, and in lieu thereof steam is either blown onto the surfaceof the material or passed through the same. During this steaming operation, it is desirable to maintain temperatures of between 250 F. and 335 -F. (preferably 280 F. to 310 F.) When themolecular weight has reached the desired point the material is withdrawn from the kettle. If desired, the product may be subjectedto further processing as m an oven. The steaming may advantageously precede the' vacuum step.

Example 6 The molecular weight of the processed chloroanacardic material of Examples 2, 3,4 or '5 may be increased by placing the material into "pans which are set into an'oven where the material is subjected to a further heat treatment. For-most applications, it is desirable to maintain an oven temperature or between 300 F. and 350F. The material gradually further thickens and then gels. The gel gradually stiffens and concomitantly therewith, particularlyif higher temperatures-are maintained, the product foa'ms' and puffs up. Considerable acrid vapor and fumesareelii'nb nated in this step. The baking operation is"'c'o':i--

' tinued until the desired degree of reaction has been obtained. If the-material is'left-in the oven long enough, it becomes hard and brittle, in which case it is particularly suitable foruse as a filler in the manufacture of frictional elements. If the product is to be used in formulating a-rubber or resin mix, the material should be removed from the oven while still soft and rubbery.

Example 7 Experimentation has disclosed that'the more highly condensed and polymerized the product is, i. e. the higher the molecularweight the strongor and more'suitable it becomesfor use as'a rubber extender or as a co-reactant for vinyl derivatives such as polyvinyl butyral or for purposes of co-curing the same with such materials. Such highly polymerized or condensed products, however, because of their high molecular weight, have such high intrinsic viscosity, that theyFare. virtually =non=peurab1e-et room "temperatures;

7 This difliculty can be circumvented by adding to the material in the kettle just prior to normal pour time an appropriate quantity of a suitable diluent in the nature of a solvent or plasticizer. Thus one may incorporate a plasticizer such as dioctyl phthalate or dibutoxY-ethyl-phthalate. The use of a quantity of plasticizer equal to the Weight of the processed chlorinated anacardic material is typical. For application where this type of product is desired, it is desirable to process chlor-anacardic material just short of the gel point.

Example 8 Chlorinated anacardic material which has had its molecular weight increased until it is in the form of a soft rubbery solid is milled upon differential rolls with appropriate compounding ingredients calculated to impart the elements of neutrality and stability to the same as well as to enhance the processing qualities. The following is a typical formulation:

' Parts Processed chlorinated anacardic material in the form of a soft rubbery material" 100.00

Zinc oxide 18.38 Magnesium oxide, light calcined 6.03 Butadiene-acrylonitrile copolymer rubber- 5.40 Plasticizer 1.32 Cerese Wax (micro-crystalline parafiin wax) 0.70

Blended waxes"; 0.40

Phenylethanolamine 0.20 Benzothiasyl disulphide 0.09 Phenylbetanaphthylamine 0.06 Stearic acid 0.06

The above ingredients, when thoroughly mill processed, yield a strong, tough, and highly flexible material which is suitable as a substitute for rubber in certain applications. The product is highly effective as an extender of rubbers of the butadiene-acrylonitrile copolymer type.

As has already been pointed out, the physical and chemical attributes of the final products are in large measure dependent upon the chlorine content of the chlorinated anacardic material as well as upon the type and quantity of other agents that may be contained in the chlorinated material. The following is a typical formulation for a chlorinated anacardic material which is preeminently adapted for use as a raw material in the production of the products of the present invention, particularly those designed for use as rubber extenders, polyvinyl acetal extenders, etc.

Parts Defoamed anacardic material 60.00 Tetrachlorethane (diluent) 50 Palm oil fatty acid 0.50 Linseed oil fatty acid 0.25 Pine oil 0.75 Chlorine 18.75

Excellent results are obtained when the chlorination is carried out in a period of between six and eight hours at a temperature of approximately 175 F.

When it is desired to produce a plasticizer, it is recommended that a smaller quantity of chlorine be introduced.

Chlorinated anacardic material, preferably aft er the molecular weight has been increased by one of the heat treatments above described, may be admixed with material such as lime, zinc oxide, magnesia, etc., to yield compositions which, when heat treated, setup to yield materials simulating slate.- Fillers such as. asbestos corporated to advantage.

By adding moderate quantities of copper oxide,

copper acetate, copper chloride, ferric chloride,

chromates, bichromates, etc., to chlorinated anacardic material, preferably after a preliminary heat treatment, it is possible, by subjecting the mixture to adequate temperatures in an oven. to obtain spongy, porous coke-like masses which may be ground up to yield the material between and 300 mesh. The products are preeminently suited for the manufacture of frictional elements, e. g., clutch facings and brake linings. In the above reactions, a substantial amount of crosslinking occurs, leading to the formation of very high molecular weight complexes.

The process of the present invention may also be carried out without the use of appreciable heat, provided that very powerful co-reactants are utilized. Thus chloro-anacardic material may be admixed with hexamethylenetetramine, strongly acidic materials, agents which liberate strongly acidic materials, or the very powerful agents belonging tothe group consisting of the saturated halogenation products of the aldehydes of the mono hetero atomic five membered rings and their reactive derivatives, and allowed to stand for a period of time. The resultant polymers are essentially of the condensation type. It is to be noted, however, that superior products result from the use of heat as disclosed in the given examples.

The condensation-polymerization products of the present invention have much higher molecular weights than the unprocessed chloro-anacardic materials from which they were derived. The chlorination of anacardic material leads to the production of substantially monomeric chlorination products. Whatever polymerizationcondensation may occur during the process of chlorination per se is of negligible import and does not appreciably alter the monomeric character of the material. Experiments have shown that in order that the condensation-polymerization exert an efiect sufiiciently large so as to enable one to readily distinguish between the original substantially monomeric product and the derived product, the mean molecular weight should be at least'double that of the original substantially monomeric material. When the molecular weight of the processed material is double that of the original substantially monomeric chlorinated material, the polymerized material acquires attributes which permit one to readily distinguish the same from the original material. In most technical applications, it is desirable to increase the weight many times over the above that of the original material. Thus, while an original product may have a mean molecular weight in the neighborhood of 600, a thick viscous product short of the rubbery point may possess a mean molecular weight in the neighborood of between 5,000 and 20,000. The molecular weights of the soft rubbery or the still harder polymers are correspondingly higher.

It is not known for a certainty whether these products are polymerization polymers or condensation polymers. There are definite indications, however, that the mechanism of polymer formation partakes of both types of polymerization. Accordingly, the products of the present invention may be described as chloro-anacardic polymerization-condensation polymers or more briefly as chloro-anacardic polymers. In the interest of clarity and brevity, the polymers of the floats may be 111-:

present eveeizl aarahereie ii s rei to as chloro-anacardic polymers.

, chloro anacardic polymers, if in theform of tors such as are used in the compounding of natural rubber, the saturated halogenation products of the aldehydes of the mono-hetero atomic five membered rings and their reactive derivatives, etc. These products may be used as substitutes for slate blackboards or, if ground up, are useful as filler in the manufacture of frictional elements.

The soft rubbery polymers are particularly suitable for use as rubber extenders or as compounding ingredients to be used in conjunction with rubber, either natural or synthetic.

The products of the present invention, particularly those processed just short of the gel point (which are conveniently used in admixture with plasticizers for the purpose of imparting a working fluidity to the whole) are preeminently suited for ec-vulcanization with polyvinyl acetals, e. g., polyvinyl butyral.

Typewriter platens containing equal parts of natural rubber and one of the foregoing chloroanacardic rubbery polymers together with the usual compounding ingredients are exceptionally tough, durable, resilient, and are capable of producing a large number of copies. They have a frictionally smooth and velvety surface not subject to rapid hardening.

Many of the chloro-anacardic polymers, particularly those of a soft rubbery nature, are suitable for use as carriers for agents which, in and of themselves cannot be conveniently handled. Thus the pungent and acrid saturated halogenation products of the aldehydes of the mono-hetero atomic five membered rings and their reactive derivatives may be readily milled into the soft rubbery chloro-anacardic polymers to yield rub- I bery products which cannot readily be handled in the conventional manner.

The softer and more fluid polymers prepared according to the present disclosure are very useful as plasticizers for a wide variety of products including natural and synthetic rubbers, the polyvinyl acetals, a wide variety of cellulosic derivatives, phenolic resins, aminoaldehyde resins, furfur-acetone resins, gum accroides resins, resins processed out of dragons blood, etc.

Many of the chloro-anacardic polymers, possessing as they do an inherent and intrinsic rubbery quality, are preeminently adapted for incorporation into a wide variety of resins, e. g. those of the phenol-aldehyde and amino-aldehyde types, for the purpose of imparting improved flexibility, decreased brittleness, and in general improved machinability. Chloro-anacardic polymers are also ideally adapted for use as fluxing agents, flow aids, and lubricants in the manufacture of molding compositions. q

Chloro-anacardic polymers may be reacted with phenols as well as with a wide variety of resins such as the phenol-formaldehyde and phenol-furfural resins to yield resinous compositions possessing new and unique qualities. Such modified resins are of particular value in applications where extensive machining is necessary as well as where high heat resistance and good electrical properties are called for.

he more ubb ry Pa me an; e u d y themselves in the manufacture of gas}; and sea n in s w l a h articl s .ergviqu made of rubber. The more fluidrpolymers which ear i 0 32 11? nature-Q uid t of tho of plasticizers, arg-1 a .-q ee rapes materials either alone, or in conjunction with l i-Q 2. ififiil a The invention has been described in connection with a-numberyof. illustrative embodiments, materials, er e i es demns-end arran me of operations for carrying 'outitsteachings. It is, therefore, to be understood that the invention is not to be restricted to the foregoing disclosure, and that no limitations are to be imported which are not required by. the language of the appended claims and the state of the prior art. It is further to be understood that the invention is not dependent upon any explanations or theories which have been set forth as descriptive of the actions involved, nor dependent upon the accuracy or soundness of any theoretical statements so advanced.

We claim:

1. The method of preparing chloro-anacardic polymers which comprises heating a substantially monomeric chlorinated anacardic material having a chlorine content of between 10% and 30% to a temperature between 240 and 350 F. until the mean molecular weight has increased to at least double that of the original chloro-anacardic material, the said heat being used as the sole agent to effect the polymerization.

2. The method of preparing chloro-anacardic polymers which comprises heating a substantially monomeric chlorinated anacardic material having a chlorine content of between 10% and 30% to a temperature between 240 and 350 F. until the mean molecular weight has increased to at least double that of the original chloro-anacardic material, and the product is substantially free of ready volatiles, the said heat being used as the sole agent to eifect the polymerization.

3. A method of preparing chloro-anacardic polymers which comprises subjecting a substantially monomeric chlorinated anacardic material having a chlorine content of between 10% and 30% to the action of heat and steam until the mean molecular weight has increased to at least double that of the original chloro-ana-cardic material and the product is substantially free of ready volatiles, the said heat being used as the sole agent to effect the polymerization.

4. The method defined in claim 1, the heating step being carried out below atmospheric pressure.

5. The method defined in claim 1, the material being subjected to the action of steam during at least part of the heating step.

6. The method defined in claim 1, the material being subjected to the action of steam during part of the heating step and being maintained below atmospheric pressure during another part of the heating step.

'7. The method of preparing chloro-anacardic polymers, which consists in subjecting anacardic material to the. action of a chlorinating agent until the anacardie material has taken up from 10% to 30% of chlorine based on the weight of the anacardic material to produce a substantially monomericchlorinated anacardic material, and after the completion of the chlorination step heating the monomeric chlorinated anacardic material until it mean molecular weight has increased to at least double that of the monomeric chlorinated anacardic material, the said heat e i2 being used as the sole agent to efi'ect the poly- UNITED'STATES PATENTS merization- Number Name Date 8. chloro-ana cardie polymers made by the 2,306,077 Novotny et aL 22,1942 method defined 1n clzklm 2,399,735 Harvey May 7, 1946 9. Chloro-anacarchc polymers made by the 5 method defined in claim 3. v I OTHER REFERENCES 7 N EM E- V Mattiello: Protective and Decorative Coatings, GEORGE K. VOGELSANG. v 1, 1, 1941, page 98,

REFERENCES CITED 1.

The following references are of record in the file of this patent:

Claims (1)

1. THE METHOD OF PREPARING CHLORO-ANACARDIC POLYMERS WHICH COMPRISES HEATING A SUBSTANTIALLY MONOMERIC CHLORINATED ANACARDIC MATERIAL HAVING A CHLORINE CONTENT OF BETWEEN 10% AND 30% TO A TEMPERATURE BETWEEN 240* AND 350* F. UNTIL THE MEAN MOLECULAR WEIGHT HAS INCREASED TO AT LEAST DOUBLE THAT OF THE ORIGINAL CHLORO-ANACARDICMATERIAL, THE SAID HEAT BEING USED AS THE SOLE AGENT TO EFFECT THE POLYMERIZATION.