The thermal polymerization of styrene at temperatures up to 250°

The kinetics of the thermal polymerization of styrene have been studied over the range 60–250°. The overall energy of activation was 86 ± 2 kJ/mole, a value identical to that obtained for the thermal polymerization of styrene in diethyl adipate. As expected, the molecular weight of the polymer decreases with increase in the temperature of the polymerization, and the ratio MwMn becomes greater than 2 for polymer formed at above 140°. The plot of log (1Mn) against (absolute temperature)−1 can be represented by two straight lines yielding 24.5 and 32,0 kJ/mole for the activation energies at temperatures below 120° and above 140°, respectively. The former value is in keeping with the molecular weight being controlled by chain transfer with monomer; the latter value would be that expected if the termination process controls the molecular weight of the polymer. Mark Houwink relationships between intrinsic viscosity and Mn and Mw have been found to apply to polymer samples when the molecular weight averages were determined by osmometry and by light scattering. However, deviations were found for low molecular weight material when measured using gel permeation chromatography. The K values were considerably lower, and the α values higher than reported in the literature.