Grafting, anionic Thermoplastics

Well characterized copolymers have been commercially available since the mid 1960 s when Shell manufactured, by anionic polymerization, SBS and SIS copolymers. Both block and graft copolymers will chain segregate due both to low entropy contributions and to lack of interactions which would favour miscibility (1). The combination of melt processability, high strength and recoverable high deformability made these and related polymers attractive alternatives to elastomers which require chemical cross-linking. A key to the behaviour of the thermoplastic elastomers is the thennally reversible association of similar chain segments into domains, which for chains below the Tg can act as cross-links. 

The hydrosilylation reaction has also been employed in the reverse way. A poly(dimethyl-siloxane) backbone exhibiting a number of silane (Si-H) functions is reacted with a polystyrene or a poly(methyl methacrylate) fitted at its chain end with allyloxy groups. The latter species can be obtained readily by reacting a living anionic polymer first with oxirane and then with allyl bromide. The hydrosilylation reaction yields poly(dimethylsiloxane- ra/t-styrene) or poly(dimethylsiloxane-graft-mQthyl methacrylate), which have been characterized as such. They exhibit typical behavior of thermoplastic elastomers over a rather broad range of compositions. ... 

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