Preparation of disyndiotactic poly(methyl crotonate) by stereospecific group transfer polymerization

Stereospecific living polymerization of methyl crotonate was achieved by us ing ketene trialkylsilyl acetals as initiators in the presence of HgI2 and iodotrialkylsilanes as catalyst and co-catalysts, respectively. ZnI2 and Cd I2 also catalyzed the polymerization. Disyndiotactic polymers with narrow m olecular weight distribution were obtained quantitatively. Livingness and s tereospecificity of this polymerization were sensitive to the structure of trialkylsilyl groups in the initiator and co-catalyst; (C2H5)(3)Si- and (n- C3H7)(3)Si- systems gave the active species with higher thermal stability a nd higher stereospecificity than (CH3)(3)Si- system. Configurational determ ination of the disyndiotactic poly(methyl crotonate)s was made by chromatog raphic separation of their low molecular weight homologs (tetramer and hexa mer), followed by X-ray single crystal analysis. The results of oligomer an alysis led to the conclusion that the disyndiotactic polymer chains are for med by the threo addition of monomers to propagating chain-ends and trans o pening of monomer C=C double bonds.