Propagation Rate Coefficients for Vinylidene Fluoride Homopolymerizations

For the first time individual propagation rate coefficients, k p, for the homopolymerization of vinylidene fluoride (VDF) have been determined in homogeneous phase reactions with supercritical carbon dioxide. Experiments combining pulsed laser initiation and polymer analysis by size-exclusion chromatography were carried out for temperatures up to 90 °C and pressures up to 1100 bar. Absolute polymer molar masses required for the determination of k p were calculated on the basis of experimentally derived Mark–Houwink constants. A general equation k p(VDF) = f(p,T) was derived by applying multiple regression analysis of k p data. All data may be expressed by ln[k p/(L·mol–1·s–1)] = 19.96 – 3633 K/T + 0.27 p/bar × T –1/K–1. Due to the fluorine atoms in the monomer the kinetic data is significantly different from the nonfluorinated structural analogue ethene. For example, at 60 °C and 1000 bar VDF k p is 19400 L·mol–1·s–1, while k p for ethene is by a factor of 200 lower.