The non-isothermal degradation kinetics of St-MMA copolymers

Styrene-methyl methacrylate (St-MMA) random copolymer in different compositions, polystyrene (PS) and polymethyl methacrylate (PMMA) particles were synthesized by suspension polymerization. The copolymer compositions were determined using nuclear magnetic resonance (H NMR) method as well as their molecular weights were examined by gel permeation chromatography (GPC). The non-isothermal degradation behavior of the synthesized copolymers was studied by thermal gravimetric analysis (TGA) under nitrogen purge and the results were compared with corresponding homopolymers. In this study it was tried to clarify the effect of St-MMA copolymer composition on the non-isothermal degradation kinetics. It was found that with decreasing the MMA content in copolymer, the molecular weight was decreased and degradation temperature in copolymer increased in all heating rates. The activation energy was calculated by the Flynn-Wall-Ozawa method. It was concluded that using the model fitting methods couldn't reveal the complexity of the thermal degradation process and the model-free methods could be a reliable way to determine the kinetic parameters. Furthermore the iso-kinetic relationship (IKR) was used to estimate a model independent pre-exponential factor (lnA) corresponding to a given degree of conversion.