Pressure and temperature dependence of the propagation rate coefficient of free-radical styrene polymerization in supercritical carbon dioxide

Free-radical polymerization of styrene in homogeneous phase of supercritical carbon dioxide (scCO(2)) has been studied at temperatures between 40 and 80 degreesC and pressures between 300 and 1500 bar. Applying pulsed-laser polymerization in conjunction with size-exclusion chromatography yields propagation rate coefficients, k(p). Within the extended pressure range under investigation, k(p) for solution polymerization in carbon dioxide, at CO2 contents up to 46 wt %, is identical to k(p) of styrene bulk polymerizations. The studies with CO2 suggest that solvent effects on k(p) occur in systems where the solvent quality for the polymer is not very high and where intrasegmental interactions are important.