Thermoplastic diene rubbers

Ethylene—Propylene Rubber. Ethylene and propjiene copolymerize to produce a wide range of elastomeric and thermoplastic products. Often a third monomer such dicyclopentadiene, hexadiene, or ethylene norbomene is incorporated at 2—12% into the polymer backbone and leads to the designation ethylene—propylene—diene monomer (EPDM) mbber (see Elastomers, synthetic-ethylene-propylene-diene rubber). The third monomer introduces sites of unsaturation that allow vulcanization by conventional sulfur cures. At high levels of third monomer it is possible to achieve cure rates that are equivalent to conventional mbbers such as SBR and PBD. Ethylene—propylene mbber (EPR) requires peroxide vulcanization. 

Tbe system may be used for homopolymers and for block copolymers. Some commercial SBS triblock thermoplastic rubbers and the closely related K-resins produced by Phillips are of this type. Anionic polymerisation methods are of current interest in the preparation of certain diene rubbers. 

In addition to the components of the vulcanising system several other additives are commonly used with diene rubbers. As a general rule rubbers, particularly the diene rubbers, are blended with many more additives than is common for most thermoplastics, with the possible exception of PVC. In addition the considerable interaction between the additives requires the rubber compounder to have an extensive and detailed knowledge concerning the additives that he employs. 

In addition to the somewhat sophisticated triblock thermoplastic elastomers described above, mention should be made of another group of thermoplastic diene rubbers. These are physical blends of polypropylene with a diene rubber such as natural rubber. These may be considered as being an extension to the concept of thermoplastic polyolefin rubbers discussed in Section 11.9.1 and although extensive experimental work has been carried out with these materials they do not yet appear to have established themselves commercially. 

Compatibilization along with dynamic vulcanization techniques have been used in thermoplastic elastomer blends of poly(butylene terephthalate) and ethylene propylene diene rubber by Moffett and Dekkers [28]. In situ formation of graft copolymer can be obtained by the use of suitably functionalized rubbers. By the usage of conventional vulcanizing agents for EPDM, the dynamic vulcanization of the blend can be achieved. The optimum effect of compatibilization along with dynamic vulcanization can be obtained only when the compatibilization is done before the rubber phase is dispersed. 

RESINS (Acrylonitrile-Butadiene-Styrene). Commonly referred to as ABS resins, these materials are thermoplastic resins which are produced by grafting styrene and acrylonitrile onto a diene-rubber backbone. The usually preferred substrate is polybutadiene because of its low glass-transition temperature (approximately —80°C). Where ABS resin is prepared by suspension or mass polymerization methods, stereospedfic diene rubber made by solution polymerization is the preferred diene. Otherwise, the diene used is a high-gel or cross-linked latex made by a hot emulsion process. 

Resols (phenol-formaldehyde resins) are commercially used for effective crosslinking of EPDM in the production of thermoplastic vulcanisates [8]. General studies on rubber crosslinking for different diene rubbers are presented here. 

The Impetus given to the block polymer field by discovery of the diene-based thermoplastic rubbers, S-B-S and S-I-S, is suggested by the data of Figure 3. Here we show a histogram of the number of... 

The choice of date range is arbitrary. The number of journal articles for each year was obtained from a search of electronic version of English-based polymer and polymer-related journals using the keywords polyolefin and blends. Within polyolefin keyword, the subkeywords used in the search were polyethylene (PE, LLDPE, LDPE, HDPE, UHMWPE, PE, etc.), polypropylene (PP, iPP, sPP, aPP, etc.), polybutene-1, poly-4-methylpentene-l, ethylene-diene monomer, ethylene-propylene-diene terpolymer, ethylene propylene rubber, thermoplastic olefins, natural rubber (NR), polybutadiene, polyisobutylene (PIB), polyisoprene, and polyolefin elastomer. For the polyolefin blends patent search, polymer indexing codes and manual codes were used to search for the patents in Derwent World Patent Index based on the above keywords listed in the search strategy. 

Rubbers, often based on poly diene rubbers or else copolymers of dienes like 1,3-butadiene, were the first successful toughening additives, and they are effective partly because they have a low modulus, 100 to 500 times lower than that of most thermoplastic polymers. Unfortunately polydienes introduce chemical double bonds which are susceptible to UV, thermal and oxidative degradation. Hydrogenation removes some of them. Acrylic compounds and ethylene copolymers are also popular impact modifiers, and they do not necessarily introduce double bonds. 

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