Synthesis of syndiotactic poly(vinyl alcohol) from fluorine-containing vinyl esters

Radical polymerization of vinyl pivalate (VPi), vinyl trifluoroacetate (VTFAc), vinyl 2,2-bis(trifluoromethyl)propionate (1), vinyl 5H-octafluorovalerate (2), vinyl 7H-dodecafluoroheptanoate (3), and vinyl 9H-hexadecafluorononanoate (4) was carried out and the tacticity of the resulting polymers was determined by H-1 or C-13 NMR analysis of poly(vinyl alcohol) (PVA) derived from the original polymers. In the bulk polymerization at 60 degrees C, the order of diad syndiotacticity of the polymers was poly(VTFAc) (57%) <poly(VPi) (60%) <poly-2, poly-3, poly-4 (61-62%) < poly-1 (65%), suggesting that steric and electrostatic effects of the fluorine-containing side groups of monomers influence the syndiotactic specificity of propagation reaction. A syndiotacticity of 69% was achieved by solution polymerization of 1 in tetrahydrofuran at 0 degrees C. This is the highest syndiotacticity reported for the radical polymerization of vinyl esters at 0 degrees C or higher temperatures. The difference of activation enthalpy (Delta H double dagger) and activation entropy (Delta S double dagger) between isotactic and syndiotactic propagations in bulk polymerization of 1 were estimated to be 460 cal mol(-1) and 0.2 cal deg(-1) mol(-1), respectively. Solvolysis rates of the vinyl esters and their polymers were also examined.