Effect of alkyl group substituents on the degradation of poly ( alkyl methacrylates ) in supercritical fluids

The effect of alkyl group substituents on the degradation kinetics of poly(alkyl methacrylates) namely poly (n-butyl methacrylate) (PBMA), poly (iso-propyl methacrylate) (PPMA), poly (ethyl methacrylate) (PEMA), and poly (methyl methacrylate) (PMMA) in supercritical and subcritical conditions was studied at various temperatures (250 – 375 o C). The molecular weight distributions were measured by gel permeation chromatography and continuous distribution kinetic models were used to determine the degradation rate coefficients. The degradation rate coefficients in the supercritical condition were found to be significantly higher than that in the subcritical condition. The degradation rate of poly(alkyl methacrylates) increased with increase in the number of carbon atom of the alkyl substituents and thus followed the order PBMA>PPMA>PEMA>PMMA. The activation energy decreased with chain length in both subcritical and supercritical conditions. The degradation of PBMA was investigated at various pressures (20 − 85 bar) at 325 C and the effect of pressure on the degradation rate coefficient was modeled using transition state theory. The degradation of PBMA was also investigated in different solvents at 325 0 C and 60 bar. The supercritical state and the density of the solvent were found to be important factors that influences the degradation kinetics.