STEREOSPECIFIC FREE-RADICAL POLYMERIZATION OF VINYL ESTERS USING FLUOROALCOHOLS AS SOLVENTS

Solvent effects on the stereochemistry of free radical polymerization of vinyl acetate (VAc) and vinyl pivalate (VPi) were investigated. In the polymerization of VAc, an alcoholic solvent with a smaller pK(a) a nd higher bulkiness afforded a polymer having a higher syndiotacticity . The polymerization of VAc in perfluoro-tert-butyl alcohol ((CF3)(3)C OH) at -78 degrees C led to a diad syndiotacticity r of 72%, which is the highest for the radical polymerization of vinyl esters. On the oth er hand, the polymerization of VPi in fluoroalcohol at a low temperatu re afforded a polymer rich in heterotacticity (up to mr = 61%). Synthe sis of a heterotactic homopolymer by the free radical polymerization o f monosubstituted vinyl monomers is unprecedented. The stereochemical effects observed in this study may be due to hydrogen-bond interaction between the fluoroalcohol molecules and the ester groups of the vinyl ester monomer and the side chain of the growing polymer, Mechanisms o f stereoregulation were proposed.