Investigation of free radical polymerization propagation kinetics by pulsed-laser polymerization

Despite the industrial importance of free radical polymerization processes, reliable values for kinetic rate coefficients remain scarce. Even for common monomers, a wide range of divergent data has been published for the propagation rate coefficient, kp, one of the most significant parameters for free radical polymerization. PLP-SEC---Pulsed Laser Polymerization (PLP) in conjunction with size-exclusion chromatography (SEC), has emerged as a robust technique for measuring these key rate coefficients in both homopolymerization and copolymerization systems and was recommended as the method of choice for the determination of propagation rate coefficient for free radical polymerization by the International Union of Pure and Applied Chemistry (IUPAC) Working party on Modeling of Polymerization Kinetics and Processes as a more direct and robust measure of kp.;In this research, the principles behind the PLP-SEC technique and the establishment of an experimental system at Queen's that uses dual detector SEC will be described. The apparatus has been used to study propagation behaviour of 4-acetoxystyrene bulk homopolymerization over a wide temperature range from 20 to 110°C, as well as to probe the kinetic mechanisms of styrene/n-butyl methacrylate both in bulk and solution copolymerization at high temperature range from 70 to 150°C. It was found that 4-acetoxystyrene has a higher kp value than styrene, and that there is a strong penultimate unit effect on the copolymerization kinetics even at high temperature.