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 1H or 13C NMR analysis of poly(vinyl alcohol) (PVA) derived from the original polymers. In the bulk polymerization at 60°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°C. This is the highest syndiotacticity reported for the radical polymerization of vinyl esters at 0°C or higher temperatures. The difference of activation enthalpy (ΔH‡) and activation entropy (ΔS‡) 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.