Vinyl pivalate Propagation Kinetics in Radical Polymerization
Hutchinson, Robin A
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Radical propagation kinetics of the bulk homopolymerizations of vinyl pivalate (VPi) and vinyl benzoate (VBz) have been studied using pulsed-laser polymerization (PLP) combined with size exclusion chromatography (SEC). As part of the study, the Mark–Houwink parameters of poly(VPi) and poly(VBz) in tetrahydrofuran are determined using a triple detector SEC. The observed significant increase (by ≈ 20%) of the bulk VPi propagation rate coefficient (kp) as pulse repetition rate is increased from 200 to 500 Hz is similar to that reported for vinyl acetate (VAc). Data collected in the temperature range of 25–85 °C for VPi is well fit by the Arrhenius relation ln(kp/L mol−1 s−1) = 15.73−2093(T/K). The activation energy is similar to that found for vinyl acetate (VAc), with kp values higher by ≈ 50%. PLP studies in ethyl acetate and in heptane find no substantial solvent effect on VPi or VAc kp values. Attempts to measure the propagation kinetics of VBz by PLP are not successful, suggesting that significant radical stabilization occurs for the system. Small-scale batch polymerization experiments demonstrate relative polymerization rates of these vinyl ester monomers that are consistent with the PLP results.