Polybutadiene, syndio

Figure 11.1 Polymer microstructures of c/s-1,4 polybutadiene, trom-1,4 polybutadiene, 3,4 polyisoprene, 1,2-polybutadiene (syndio- and isotactic).

An unusual method for the preparation of syndiotactic polybutadiene was reported by The Goodyear Tire Rubber Co. (43) a preformed cobalt-type catalyst prepared under anhydrous conditions was found to polymerize 1,3-butadiene in an emulsion-type recipe to give syndiotactic polybutadienes of various melting points (120—190°C). These polymers were characterized by infrared spectroscopy and nuclear magnetic resonance (44—46). Both the Ube Industries catalyst mentioned previously and the Goodyear catalyst were further modified to control the molecular weight and melting point of syndio-polybutadiene by the addition of various modifiers such as alcohols, nitriles, aldehydes, ketones, ethers, and cyano compounds. 

Other symbols occasionally used in the literature include (br) for branched materials and (iso), (syndio), and (a) for isotactic, syndiotactic, and atactic structures respectively. No symbol appears to exist for mechanical blends, although these materials are obviously important. Where necessary the symbol -m- will denote a mechanical blend, for example, poly(styrene-m-butadiene) for a mechanical blend of polystyrene with polybutadiene. 

Depending on the selected method, the polymerization of conjugated dienes can lead to various isomers of the monomeric units shown hereafter depending on whether the residual double bonds are localized either laterally or in the main chain, one can obtain polyvinyl (iso- and syndio-) tacticity or geometrical type isomerisms, respectively, that are presented hereafter. They exhibit different chemical and physicochemical properties. Actually, polybutadienes contain variable proportions of each one of these structures and can thus be assimilated to statistical copolymers whose properties vary continuously with respect to their composition. 

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