Abstract
Stereospecific living polymerization of methyl crotonate was achieved by using ketene trialkylsilyl acetals as initiators in the presence of HgI2 and iodotrialkylsilanes as catalyst and co-catalysts, respectively. ZnI2 and CdI2 also catalyzed the polymerization. Disyndiotactic polymers with narrow molecular weight distribution were obtained quantitatively. Livingness and stereospecificity of this polymerization were sensitive to the structure of trialkylsilyl groups in the initiator and co-catalyst; (C2H5)3Si- and (n-C3H7)3Si- systems gave the active species with higher thermal stability and higher stereospecificity than (CH3)3Si- system. Configurational determination of the disyndiotactic poly(methyl crotonate)s was made by chromatographic separation of their low molecular weight homologs (tetramer and hexamer), followed by X-ray single crystal analysis. The results of oligomer analysis led to the conclusion that the disyndiotactic polymer chains are formed by the threo addition of monomers to propagating chain-ends and trans opening of monomer C = C double bonds.
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