Chain transfer with carbon tetrabromide in the polymerization of styrene

Abstract

Previously reported values of 1.36-2.7 at 60°C for the chain transfer constant C_s for styrene polymerization in the presence of carbon tetrabromide have been shown to be in error due to excessive extents of conversion. Most of the carbon tetrabromide is consumed by 0.5-0.7 % polymerization and subsequent reaction probably approximates to bulk polymerization. Restriction of the extent of conversion to 0.5 % gives an estimated value of 420±60 for C_s, which is independent of temperature. The activation energy and frequency factor for the chain transfer reaction of polystyrene radicals with carbon tetrabromide is 33 ± 7 kJ mol^–1 and 9.2 × 10⁹ 1.mol^–1 s^–1 respectively. The effect on the freeze-dried polymer of precipitation in methanol has been investigated.