An experimental study of the high-temperature polymerization of styrene in a CSTR, investigating the effect of reaction temperature(260-343 degreesC), and residence time (5-90 min) on monomer conversion and average molecular weight and distribution is reported. A kinetic analysis of these experimental data demonstrates that the dominant chain production reaction is backbiting followed by beta-scission. In this reaction series, a chain end radical abstracts a hydrogen in a characteristic location down the chain, and subsequently undergoes beta-scission, producing two smaller fragments, a radical and a terminally unsaturated polymer chain. It is found that the large variation of the average molecular weight observed in the considered range of operating conditions is strongly correlated to the ratio of the rate of propagation to that of backbiting/beta-scission. Further kinetic analysis, based on the estimated activation energy of 77.5 kJ/mol for this reaction series, suggests that beta-scission is the rate controlling step.