Polymerization, elastomer synthesis copolymerization

The synthesis of elastomers by step, chain, and ring-opening polymerizations is reviewed. These reactions are characterized as to the process variables which must be controlled to achieve the synthesis and crosslinking of an elastomer of the required structure. Both radical and ionic chain polymerizations are discussed as well as the structural variations possible through copolymerization and s tereoregularity. 

Polyaddition of organosilicon dihydrides, mainly dihydro(poly)siloxanes to dialkenyl-substituted organic compounds also known as hydrosilylation copolymerization, leads to polycarbosiloxanes with functionalized organic segments (359). Platinum-catalyzed polymerization hydrosilylation of a,allyl-substituted bisphenols, imides, or amides leads to the synthesis of block copolymers that are useful thermoplastic elastomers (Scheme 40). 

Here, we report on the synthesis and characterization of PMMA-poly(/i-butylacrylate)-PMMA (MBuM) symmetric triblock copolymers, as a new family of thermoplastic elastomers. These compounds have be prepared by a novel route based on controlled radical polymerization [4]. Compared to classical anionic living polymerization [5], this new route, sketched in Scheme la, appears particularly appealing since the triblock copolymers are prepared in a two-step process instead of the usual three steps required in anionic polymerization. In the latter case, as butylacrylate cannot be polymerized via a living process, the MBuM symmetric triblocks have to be synthesized by sequential copolymerization of er butylacrylate (tBuA) and MMA followed by the transalcoholysis of the tBu esters with n-butanol... 

The anionic arm-first methods can also be applied to the synthesis of star block copolymers [59]. The procedure is identical except that living diblock copolymers (arising from sequential copolymerization of two appropriate monomers, added in the order of increasing nucleophilicity) are used as living precursor chains. The active sites subsequently initiate the polymerization of a small amount of a bis-unsaturated monomer (DVB in most cases) to generate the cores. If polystyrene and polyisoprene (or polybutadiene) are selected, the resulting star block copol)miers behave as thermoplastic elastomers because of their different glass transition temperatures. 

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