Plastics from Natural Rubber 6. Salomon, 6. J. van Amerongen, C . J. van Veersen, 6. Sohuar. and H. C. J. de Decker Rubber FoundatJon, Delft, Holland
a
Methods for the preparation of rubber derivatives from acid-stabilized natural latex are discussed. Usually the primary reaction product consists of particles corresponding in size with the original, slightly cross-linked macromolecules in the latex globules and are therefore insoluble. A s a consequence, the technology of latex derivatives differs considerably from that of the same or a similar derivative prepared in solution. Latex-chlorinated rubber has a lower chlorine content and a slightly lower stability compared with the classic product prepared in solution. I t is often virtually insoluble in the conventional paint vehicles, because of a slight amount of cross linking. On the other hand, from the product a stable latex can be obtained, which makes
new applications possible. Properly soluble chlorinated rubbers of high chlorine content (up to 70%) are obtained by means of an aftertreatment of latex-chlorinated rubber. Rubber hydrochloride from latex is a powdery product with a high degree of crystallinity. Part of this crystallinity persists even near the decomposition temperature at 130" C. Processing methods have therefore to be adapted to these general properties, which resemble those of saran. Several applications have been developed. Cyclized rubber from latex, a thermoplastic, finely divided powder, can be processed with softeners of the paraffinic oil type and with cheap fillers. I t differs from the known derivative by its remarkable reinforcing effect on rubber, when mixed in the form of a latex with rubber latex.
D
the application or the development of acid. Hevea latex is in general stabilized with ammonia and coagulates very easily with acid. To avoid coagulation by acid, special stabilizers have to be added-e.g., nonionic stabilizers or cationic soaps which are added in amounts of 1 t o 5% relative t o the rubber. The incorporation of these emulsifiers prevents the coagulation of the latex on addition of acid, although the latex loses much of its stability. At higher acidities (above approximately 6 N relative t o the water phase) the stability of the latex again begins t o increase considerably. Probably at these higher acidities charge reversal gives the proteins of the rubber particles new stabilizing power, which is then added to that of the emulsifier. Indeed, it can be shown that the sign of the charge carried by the rubber particles is reversed from negative t o positive when the latex is acidified. The acid-resistant latex thus obtained can be used for the preparation of several rubber derivatyves, which formerly could be prepared only from rubber in solution or from solid rubber.
URING nearly 12 years chemical research in the authors'
laboratory has been focused on three basic problems: ( 1 ) fundamental research concerning the influence of chemical modification of natural rubber on structure and mechanical properties; ( 2 ) the preparation of rubber derivatives starting from latex; and (3) the development of a technology of these latex rubber derivatives. Much of the line of thought was influenced by the first Rubber Technology Conference in 1938, where rubber derivatives and synthetic rubbers were discussed together for the first time. At the same conference Blow (6) demonstrated the use of cationic soaps with latex. A full review of the knowledge on natural rubber derivatives has been given recently by Le Bras and Delalande ( l a ) .
Preparation of Rubber Derivatives from Latex General Method. The preparation of rubber derivatives from latex meets the difficulty that most reactions with rubber involve
315
INDUSTRIAL AND ENGINEERING CHEMISTRY
316
Generally the concentration of the rubber in the latex can be varied widely. Commercial latex of a 60% concentration is often very suitable for the purpose. Chlorinated Rubber. Chlorinated rubber can be prepared from stabilized latex by passing gaseous chlorine through it after it has been strongly acidified ( 1 ) . The temperature of reaction may vary from -10' up t o 1 1 0 0 " C., a temperature of about 20" C. being very satisfactory. After some hours a stable chlorinated rubber latex is obtained. Acidification of the latex before the reaction is necessary t o avoid the formation of hypochlorous acid, which might be formed according to the equation ( I S ) . Clz
+ OH--
HOC1 f C1-
The equilibrium of the reaction may be expected to shift t o the side of the chlorine upon the addition of hydrogen or chlorine ions. Consequently, the formation of hypochlorous acid in the latex can be prevented byadding an excess quantity of theseionse.g., in the form of hydrochloric acid-an amount of a t least 3 gram-equivalents of acid per liter of latex being preferred. Sulfuric acid can also be used. The degree of acidity increases on chlorination because of the development of hydrochloric acid in the substitutive reaction of chlorine with rubber. The presence of hypochlorous acid is undesirable because i t reacts with rubber t o form an unstable hypochlorinated rubber. Another advantage of high acidity of the latex is the increased mechanical stability it brings about. However, saturation of the latex with hydrochloric acid should be avoided in this case t o prevent hydrochlorination of the rubber. Sulfuric acid a t too high a concentration would cyclize the rubber. The chlorinated rubber can be isolated from the latex by precipitation with alcohol or by warming, preferably after addition of a sodium chloride solution. The chlorine content of the chlorinated rubber depends on the amount of chlorine applied and may reach as much as 61%. Usually the dry product is a finely divided white powder. It swells strongly in solvents like carbon tetrachloride and chloroform, indicating a slight amount of cross linking. The chlorine content of the latex-chlorinated rubber can be increased up to 65 or 7oY0 by an aftertreatment, during which the chlorinated rubber can be broken down to a product with sufficiently low viscosity in solution t o be applied in paints. Patent applications are pending. Hydrochlorinated Rubber. By saturating stabilized latex with hydrochloric acid for about 48 hours at room temperature, rubber hydrochloride is formed ( 2 4 ) . It is necessary t o keep the latex saturated with hydrochloric acid, because only in that case nonionized hydrochloric acid is present to react with the rubber. The time of reaction can be decreased considerably by applying a higher temperature and some pressure. The reaction product is obtained in the form of a stable latex, consisting of a dispersion of rubber hydrochloride. The dry product, which can be isolated from the latex in the same way as described for chlorinated rubber, is a white powder, containing up t o 33% of chlorine-i.e., over 95% of the theoretical amount. Like the rubber in latex itself, rubber hydrochloride from latex is slightly cross-linked. Cyclized Rubber. Sulfuric acid is added rapidly to stabilized latex until the water phase of the latex contains about 75 weight yo of sulfuric acid. The mixture is heated to about 70" to 100' C. for some time during which a rapid cyclization reaction of the rubber takes place (23). The reaction product is again obtained in the form of a stable latex, from which the cyclized rubber can be isolated by filtration after dilution. The dry product is a finely divided, yellow-white insoluble powder, which is easily redispersible in water t o a latex. Usually i t contains 0.5 t o 1% of sulfur partly combined in acid groups. These acid groups should be neutralized with alkali during the isolation process. The degree of cyclization depends on the conditions of reaction-vie., the degree of acidity, the temperature,
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and the time. A nearly complete cyclization is obtained after reaction for 2 hours a t 100" C. a t an acidity of 7501, by weight. Independently a similar method of preparation of c j clized rubber from latex has been found by Gordon (8). Formaldehyde Reaction Products of Rubber. A reaction takes place after formalin has been added to hydrochloric acidacidified latex with formation of a rather coarse suspension of a rubber derivative. This derivative appeared to consist of a powdery, insoluble, nonthermoplastic compound, and mav be the result of the following reaction (9, 10):
>=
I
C-
6
C1 CH,OH
No application of the product has been found. A similar product can be obtained, using sulfuric acid as the acidifying agent. Rubber Hydroxy Compounds. On addition to a 60% stabilized latex of double the amount of 30y0 hydrogen peroxide and subsequently a fourfold amount of acetic acid, a reaction takes place. The best conditions for the reaction are about 24 hours a t 60' C.; a lower temperature requires a longer time. A small amount of sulfuric acid catalyzes the reaction strongly. After the reaction the rubber of the latex appears t o be dissolved in the serum. The reaction product can be isolated from this solution after precipitation with water. The white powdery product appears t o be of rather low molecular weight, judging from its intrinsic viscosity in chloroform of 0.05. I t s oxygen content is about 30% and its saponification number about 100. From this it can be calculated that per isoprene unit about 1.65 hydroxyl groups and 0.2 acetate group are present. Its structure probably is:
L
OH OH
Part of the hydroxyl groups are apparently esterified. Sinlilar products are described in the literature (6,11). A product containing only hydroxyl groups can be prepared on adding a mixture of hydrogen peroxide and sulfuric acid t o latex instead of hydrogen peroxide and acetic acid. Cyclization of the rubber should be avoided in this case.
Chemical Structure of Rubber Derivatives Kinetic Analysis. A new tool was used in extensive studies on rubber halides: the identification of halide structures by kinetic analysis ($0). This method is based essentially on the fact that the rate of reaction of primary, secondary, tertiary, allylic, and vinylic halide groups with aniline, pyridine, or piperidine is a characteristic property of the group and can therefore be used t o estimate the amount of different halide groups in the same polymer chain. Within certain limits it can be extended to the identification of different types of polychlorides. I t s application in elucidating the structures of chlorinated and hydrochlorinated polymers is discussed below. Chlorination. The reaction of rubber with bromine and iodine chloride is essentially an addition to the double bond; chlorination, however, has a more complicated character. Kinetic analysis with aniline proved that the structure of reaction products of rubber in latex and chlorine differs only slightly from the classical chlorination products prepared from rubber in solution. In both cases the first chlorine atom is introduced in the isoprene unit of the rubber molecule by substitution in place of a n allylic hydrogen atom, leaving the number of double bonds unchanged. This primary reaction product is generally very unstable. Theoretical considerations (8, $8) make a polar course of the reaction probable in which the double bond is shifted:
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1951
CHz -CHz-C
I
= CH-CHZ-
+ C1,
---+
CHz It
-cH~-~-cH-cH~-
CE Cl
I
. e
C1@
\
CH3 I -CH=C-CH-
C H r I
Some cyclization may also occur. A decision between the two reaction products, IIa and IIb, which could be formed from the hypothetical intermediate, I, has become possible with t h e aid of ~ infrared analysis (81). It is found t h a t the original 1 2 absorption band for the rubber double bond is replaced by a new strong llp band typical of the vinyl group. This would indicate t h a t IIa is the main primary reaction product. This product is gradually transformed on further chlorination into a stable chlorinated rubber. Again infrared analysis reveals the presence of residual double bonds, even at a chlorine content of 70%. This indicates t h a t the process of substitutional addition is repeated (111)besides addition to the double bond (IV):
solid rubber, of rubber in solution, and of rubber in latex at temperatures as low as -70" C. and as high as 100' C. No trace of the presence of a secondary chlorine atom, as suggested in the literature ( l a ) ,has ever been found. Polybutadiene and GR-S on the other hand react only a t higher temperatures and pressures with hydrochloric or hydrobromic acid (80)with formation of complicated structures with large secondary chlorine fractions. The fact that 3 t o 6% of the double bonds of natural rubber do not react with hydrochloric acid might indicate t h a t these double bonds have a different structure. We may assume that in the first stage of the typical polar reaction between natural rubber and hydrochloric acid the r-electrons of the natural rubber double bond form a coordination complex with hydrochloric acid. This complex formation can be formulated ( 2 4 ) as follows:
CH3
I
-CHS-C-CH-CHz..
+-
-
I
c1 The availability of nelectrons a t the rubber double bond is also demonstrated by the ease of reversible complex formation with silver nitrate and silver perchlorate (16). Cyclization. Cyclization of natural rubber is a polar reaction which is related t o the hydrochlorination reaction (85). I n the first step of the reaction a rubber carbonium ion is formed under influence of the strongly proton donor properties of the cyclizing agent-e.g., sulfuric acid.
I
I
--CHZ--
-CHz-C-CHZ--CHz-
-CHz-C=CH-CHz-
-CHZ-C=CH-CHt-
j+
CHs
'333
CH3
C-CH [?"H CI
This complex is easily transformed into the final product:
I
Structural units of the I11 type are the cause of the chemical instability of chlorinated rubber with 50 t o 60% chlorine. Saturated and therefore less reactive isomers of the same chlorine content have been obtained by chlorination (act,ivated by ultraviolet light) of rubber hydrochloride or of rubber dichloride (9). The synthesis of the rubber dichloride becomes possible b y the radical initiated addition of chlorine from sulfuryl chloride t o rubber in solution ( 2 , 4).
f HCI C-
-CHz-
CHzCl -CHz-C-CH-CHz-
317
--HzSO4
peroxide
+ SOClz -* CH3 I
the second step of the reaction this very unstable carbonium -cH,-LcH-cH~+ soe ionI ncyclizes as follows: I t c1 c1 CH, This dichloride can be distinguished from the product of direct chlorination by its much higher stability toward aniline at 100O C. Unfortunately, i t is not possible t o carry out this dichlorination reaction in latex because of the fast decomposition of sulfuryl chloride in water. Hydrochlorination. Natural rubber, especially in solution, adds hydrochloric or hydrobromic acid with great ease even at very low temperatures. Kinetic analysis confirmed t h a t all chlorine atoms of rubber hydrochloride are fixed a t the tertiary carbon atom, in accordance with the rule of Markownikoff. This tertiary structure has been obtained by hydrochlorination of
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318
It is obvious that this reaction may continue till the formation of a chain of ring structures. It may be possible that a cyclized rubber molecule contains several groups of rings separated by unchanged isoprene units.
Structure and Mechanical Properties Several structural factors vhich influence the mechanical properties of high polymeric materials can be distinguished (18): molecular weight , degree of cyclization, intermolecular forces, presence of double bonds, and crystallinity. Molecular Weight. The mechanical properties of thermoplastic polymers improve with increasing molecular weight. Latex technology offers the obvious advantage of preserving the high molecular weight of the starting material in the derivative, the hydroxy compounds being a notable exception. Rubber in the form of ammonia-preserved latex is slightly cross-linked and so are most derivatives; nevertheless, they are essentially thermoplastic. Degree of Cyclization. The absence of rubber elasticity and the high softening point of cyclized rubber are due to the loss of chain flexibility and the formation of bulky 6-rings in the chain. From the structural formula it can be understood that the properties are more or less similar to the high-styrene copolymers and the low molecular resins like damar, rosin, or copal (65). The large molecular size makes the polymer less brittle a t 20' C. than these latter resins. Intermolecular Forces and Presence of Double Bonds. The addition of polar groups to the double bonds of rubber leads t o an increase in the brittle point. As loss of double bonds by itself reduces chain flexibility, it is difficult to evaluate the stiffening effect of polar groups alone. The first phase of chlorination, however, leads to the allylic chloride, I l a , which can be compared with neoprene. CHz
ll
-CHz-C-CH-CHZI dl
(114
-CHZ-CH=C-CH2I
GI Seoprene
It is found that I I b is only a "sloiv" rubber-i.e., a rubber with a low rate of recovery a t 20" C. Apart from the difference in the position of double bonds between IIa and neoprene, bulky side groups such as methyl or vinyl groups reduce the flexibility of the chain. This rather unexpected influence of methyl groups hecomes evident in the properties of polymers from dienes and their copolymers (17, 19). The brittle point increases by a t least 20' t o 30" C. for each methyl group in the series polybutadiene < polyisoprene < polydimethylbutadiene. LOBE of rubber elasticity on chlorination can generally be understood as a combined effect of polar chlorine groups and double bond shifts, cyclization being an additional essential factor. This explains why chlorinated rubbers with 50 t o 60% chlorine are hard, rather brittle materials, which soften at 50" C. Crystallinity. Crystallization of high polymers affects the mechanical properties strongly. The crystallized areas act as a kind of cross link between the polymer molecules, which increase tensile strength strongly and decrease flow. Generally, stretching of the high polymeric material increases crystallization considerably, because during the stretching process the chain molecules are pulled in a parallel orientation favorable to crystallization. Such a n orientated crystallization explains the good mechanical properties of many fibers. The crystallinity of rubber and gutta-percha hydrochloride has been extensively studied by Gehman el al. (7). A11 synthetic polyisoprene hydrochlorides are amorphous, although the chlorine is tertiary and the lattice of the rubber hydrobromide is identical with t h a t of the hydrochloride. This proves t h a t the regular pattern of the chain is one decisive factor for the ease of crystal-
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lization. The authors surmise that the similar size of chlorine and methyl groups is the second factor; probably both groups are interchangeable in the lattice. The special symmetry of the hydrochloride then becomes similar t o that of polyvinylidene chloride (saran):
-C-CH~-CH~-CH~--
I c1
Rubber hydrochloride
C1 c1 I I -C-CH~-C-CH~--
I!!(
I
c1
Polyvinylidene chloride
In both cases irregularities in the molecules reduce the amount of crystalline phase. In fact, the technology of both plastics is very similar Another promising crystallizable rubber derivative is the SO2 adduct. The technical value of a new type of oriented fiber ( 1 4 ) made from this material is based on its crystallinity. A third group of spontaneously crystallizing derivatives is the complexes of rubber with silver nitrate and silver perchlorate (16). Here again the natural polymer chains, rubber and guttapercha, yield crystalline products, while all other polymer complexes are amorphous (15).
Technology of Latex Rubber Derivatives Chlorinated Rubber. The primary product of chlorination in latex is much less soluble than the well-known chlorinated rubber prepared from solution. There is also a difference in chlorine content, heat stability, and aging properties. I t is therefore necessary t o break down the primary product, whenever it must be applied as a soluble paint vehicle. This breakdown can be carried out successfully and with simultaneous afterchlorination t o as much as 70% chlorine by a suitable chemical treatment (patent application pending). On the other hand, from the primary product a stable latex can be easily obtained, which can be used as such; in this case the advantage of the original high molecular weight is conserved. Coatings, films, and other products can be manufactured easily. The films and coatings are uniform and tight; their resistance t o alkali and mineral oil is as good as that of films from soluble chlorinated rubber; and their water vapor permeability and softening temperature are dependent on the manufacturing process. Rubber Hydrochloride. The methods of processing rubber hydrochloride from latex must be based on the following facts. The molecular weight is very high and the molecules are to some extent cross-linked. The material has a high degree of crystallinity, even near the softening temperature of about 120' C. Decomposition begins at about 130" C . The material is sensitive to light and in several respects closely resembles saran. The chemical resistance is generally very good a t room temperature and a t slightly elevated temperatures; resistance to oxidizing reagents is only moderate. The methods of processing can be divided into two groups-hot processing and cold processing. For hot processing, in which the material must flow easily in a not too narrow temperature range, it is necessary to break down the hydrochloride molecules. This can be done by milling; the milling process must be controlled in order t o avoid decomposition with loss of hydrochloric acid. The improvement of flow can be enhanced by the addition of suitable softeners or fillers. The decomposition reaction in which hydrochloric acid is evolved is autocatalytic and is also accelerated by Friedel-Crafts catalysts like ferric chloride or zinc chloride; the decomposition may be counteracted by basic substances such as magnesium oxide and amines, which act as heat stabilizers. The decomposition is also promoted by water, so that the material t o be milled must be dry. After the milling process the material can be pressed, calen-
February 1951
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INDUSTRIAL AND ENGINEERING CHEMISTRY
dered, injection molded, or extruded a t temperatures between 100' and 130O C., although not very easily. The photostability of the products can be improved b y photoinhibitors or by pigments, t h a t may also be added for other purposes. All products have a fair amount of crystallinity, and softeners can be incorporated only t o a limited extent; macromolecular softeners can be used t o counteract crystallization, especially the aftercrystallization that results in a n often undesirable gradual hardening of the products. Several applications, like floor tiles and pipes, have been developed on a semitechnical scale. Various methods of low temperature processing have been worked out. The products obtained in this way still possess the original high molecular weight and stability. Films and various other products of remarkable mechanical properties have been manufactured on a semitechnical scale; full advantage can be taken of the possibility of producing highly oriented products from the crystalline polymer (patent application pending). Cyclized Rubber. The technology of latex cyclized rubber has been studied from the following points of view. Its use as a plastic as such is difficult because i t starts t o soften considerably a t 50" C., whereas it does not flow easily at temperatures considerably above 50" C. Only little improvement of flow properties results from milling of the material; better results may be obtained after addition of softeners of the paraffinic oil type and cheap fillers. The most interesting application of latex cyclized rubber found up t o this moment is its use as a reinforcing filler in rubber. The best method of using it for this purpose is t o mix rubber latex and a cyclized rubber latex. This intimate mechanical mixture of latices can be processed and vulcanized as a n ordinary rubber latex, or i t can be dried and then treated according t o normal solid rubber technology. These combinations of rubber and cyclized rubber have very remarkable mechanical properties (26). The modulus at 300% elongation of a 70 rubber-30 cyclized rubber vulcanizate is high (150 kg. per sq. cm.), resilience is good (75% Ltipke), and heat build-up is rather low (20" t o 25" C. Goodrich flexometer )
.
319
Literature Cited (1) Amerongen, G. J. van, Brit. Patent 634,241 (1950). (2) Amerongen, G. J. van, and Koningsberger, C., J . Polymer Sci., 5, 653 (1950). (3) Amerongen, G. J. van, Koningsberger, C., and Salomon, G., Ibid., p. 639. (4) Bloomfield, G. F.,J . Chem. SOC.,1944,114. (5) Bloomfield, G. F.,and Farmer, E. H., J . SOC.Chem. Ind., 53, 121T (1934). (6) Blow, C. M.,Proc. Rubber Tech. Conf. London, 1938,186. (7) Gehman, S. D., Field, J. E., and Dinsmore, R. P., Ibid., p. 961. (8) Gordon, M.,IND.ENG.CHEM.,43,386 (1951). (9) Hirano, Sumito, and Oda, Ryohei, J . SOC.Chem. I d . J a p a n , 47, 833 (1944). (10) I. G. Farbenindustrie, Dutch Patent 44,662(1938). (11) Kambara, Shu, et al., J . SOC.Chem. I n d . J a p a n , 46,41-4,676-84, 761-7 (1943); Bull. Rubber Research Znst. Japan, No. 1, 14 (1945). (12)Le Bras, J., and Delalande, A., "Les DBrivbs Chimiques du Caoutchouc Naturel," Paris, Dunod, 1950. (13) Morris, J. C.,J . Am. Chem. SOC.,68, 1692 (1936). (14) Rumscheidt, G. E., and Nie, W. L. J. de, Dutch Patents 59,013, 59,323,59,325,59,731 (1947); U.S. Patent 2,469,847(1949). (15) Salomon, G.,Chimie et Industrie, 63, 567 (1950); 21st Congr. Intern. Chimie Industrielle. (16) Salomon, G., Discussions Faraday SOC.,2,353 (1947); Rec. trav. chirn., 68,903(1949). (17) Salomon, G., J. Polymer Sci., 3,32 (1948). (18) Salomon, G.,Schweiz. Arch. angew. Wiss. u. Tech., 16, 161 (1950). (19) Salomon, G.,and Koningsberger, C., J . Polumer Sci., 2, 522 (1947). (20) Salomon, G., Koningsberger, C., and UltBe, A. J., Proc. Second Rubber Tech. Conf. London, 1948,106; Rec. trav. chim., 69,95, 711 (1950). (21) Salomon, G.,Sohee, 8.C. van der, Ketelaar, J. A. A., and Eyk, B. J. van, Discussions Faraday Soc., in press, (22) Taft, R. W.,J . Am. Chem. SOC.,70,3364 (1948). (23) Veersen, G. J. van, J . Polgmer Sci., 5,S23 (1950). (24) Veersen, G. J. van, Proc. Second Rubber Tech. Conf. London, 1948,87. (25) Veersen, G. J. van, Rec. trav. chim., 69, 1365 (1950). (26) Veersen, G. J. van, and Boonstra, B. €4. S. T., Rubber A g e , 68,57 (1950). RECEIVEDOctober 4, 1950. Communication 149, Rubber-Stichting.
ButadieneDStyrene Resinous Copolymers 4
-
Although high-styrene resins have become of great commercial importance during the past 5 years (approximately 25,000,000 pounds manufactured in 1949), comparatively little information on the polymerization processes or any systematic review of their properties can be found in the technical literature. The object of the present paper is to supply such information. A series of butadiene-styrene copolymers with charging ratios of 50/50, 40160, 30170, 20180, and 10/90 was prepared. Polystyrene, prepared under the same conditions, was included as a control. Properties of the latices and resins obtained, presented in a systematic manner, were found to be largely dependent on the monomer ratio employed in the polymerization. For the first time a coherent picture is presented of the entire plastic range of the styrene-butadiene resins. This should encourage the further development of this large and expanding field, which includes such applications as natural and synthetic rubber reinforcing, impact resistant compositions, protective coatings, and latex paints.
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J. D. D'Ianni, L. D. Hess, and W. C. Mast The Goodwear Tire & Rubber Co., Akren, Ohio
I
N THE past 5 years resinous copolymers of butadiene and
styrene have become of great commercial importance. This development has been spurred by the availability of these monomers in large quantities and a t low prices as a result of the synthetic rubber program sponsored by the Government in cooperation with the rubber and chemical industries. I n the period before World War 11, the rubber industry had become interested in resinous copolymers, particularly those obtained by chemical reactions of natural rubber. At t h a t time were developed such products as chlorinated rubber (Parlon, Hercules Powder Co.), cyclized rubber (Pliolite, Goodyear Tire & Rubber Co., and Marboq, Marbon Corp.), and rubber hydrochloride (Pliofilm, Goodyear Tire & Rubber Co.). Cyclized rubber has been of special interest as a rubber reinforcing agent and a s the vehicle or binder for pigments in special protective coatings, such as concrete paints and corrosion-resistant coatings.
