Homopolymers, unsaturated Polybutadiene

This combination of monomers is unique in that the two are very different chemically, and in thek character in a polymer. Polybutadiene homopolymer has a low glass-transition temperature, remaining mbbery as low as —85° C, and is a very nonpolar substance with Htde resistance to hydrocarbon fluids such as oil or gasoline. Polyacrylonitrile, on the other hand, has a glass temperature of about 110°C, and is very polar and resistant to hydrocarbon fluids (see Acrylonitrile polymers). As a result, copolymerization of the two monomers at different ratios provides a wide choice of combinations of properties. In addition to providing the mbbery nature to the copolymer, butadiene also provides residual unsaturation, both in the main chain in the case of 1,4, or in a side chain in the case of 1,2 polymerization. This residual unsaturation is useful as a cure site for vulcanization by sulfur or by peroxides, but is also a weak point for chemical attack, such as oxidation, especially at elevated temperatures. As a result, all commercial NBR products contain small amounts ( 0.5-2.5%) of antioxidant to protect the polymer during its manufacture, storage, and use. 

Synthetic rubbers are produced as commodities. Polybutadiene, polybutylene, polychloroprene and polyepichlorohydrin are examples of elastomeric homopolymers. Copolymeric rubbers comprise poly-(butadiene-co-styrene), poly(butadiene-co-acryloni-trile), poly(ethylene-co-propylene-co-diene), and poly-(epichlorohydrin-co-ethylene oxide). The unsaturated group in the comonomer provides reactive sites for the crosslinking reactions. Copolymers combine resilience with resistance to chemical attack, or resilience in a larger temperature range, and thermoplastic-like properties. There are several studies in the literature describing the preparation of blends and composites of elastomers and conductive polymers. A description of some significant examples is given in this section. 

Ozonisation is an extremely useful technique for the elucidation of sequencing in unsaturated homopolymers. Use of the technique is illustrated below by a discussion of results that have been obtained by applying the technique to polybutadiene and polyisoprene. 

ESR spectroscopy has been applied to studies of unsaturation and other structural features in a wide range of homopolymers including polyethylene [101-110], polypropylene [111-121], polybutenes [115], polystyrene [122-124], PVC [125,126], polyvinylidene chloride [127], polymethylmethacrylate [128-137], polyethylene glycol polycarbonates [137-140], polyacrylic acid [136-139, 141, 142], polyphenylenes [143], polyphenylene oxides [143], polybutadiene [144], conjugated dienes [145,146], polyester resins [146], cellophane [143,147] and also to various copolymers including styrene grafted polypropylene [148], ethylene-acroline [149], butadiene-isobutylene [150], vinyl acetate copolymers [151] and vinyl chloride-propylene. 

Furthermore, the norbornene derivatives could be polymerized in the presence of unsaturated polymers like polybutadiene or styrene-butadiene copolymer(SBR) to give block or graft copolymers. The formation of the block(graft) copolymer was substantiated by the electronmicroscopy, which revealed a two-phase structure of the products in the solid state. The block copolymerization with a unsaturated rubbery polymer was successfully utilized to improve the impact resistance of the homopolymers of norbornenenitriles. 

The products have superior mechanical properties compared with the random copolymers or blends of homopolymers of the same overall composition. The literature reports block copolymers of polybutadiene with cyclopentene [69a], cyclooctadiene [69b], cyclodo-decene [69c] and substituted norbornenes [69d], of polyisoprene, polychloroprene, polypentenamer, and butyl rubber with norbornene derivatives [69c] and styrene-butadiene copolymers with cyclopentene [69a] and norbornene derivatives [69c]. Graft copolymers of type (103) will arise when unsaturation occurs in branched arms of the polymer to be grafted (e.g., 1,2-polybutadiene with cycloolefins) ... 

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