Gel effect in free radical polymerization: Model discrimination of its cause

A mathematical model was developed to compare free radical polymerization conversion-time data to predictions based on different physical processes likely controlling termination. Comparison of the isothermal experiments showed that methyl methacrylate (MMA) formation of higher M polymer leads to a stronger C-dependence for k_t. For styrene, the C-dependence of k_t appears far too weak to be described by monomeric radical or segmental diffusion. This may be associated with short-long termination, as substantial chain transfer in styrene polymerization may result in a population of short, very mobile chains, enhancing termination and lowering of its C-dependence.