Thermal degradation studies of poly(urethane-siloxane) thermosets based on co-poly(dimethyl)(methyl, hydroxypolyoxyethylenepropyl) siloxane

A series of crosslinked hybrid poly(urethane-siloxane) networks based on comb-like structure co-poly (dimethyl)(methyl, hydroxypolyoxyethylenepropyl) siloxane cured with aliphatic diicocyanates hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and 4,4'-methylenebis(cyclohexyl isocyanate) (H12MDI), were obtained. The samples have been submitted to thermal stability investigations at non-isothermal conditions in nitrogen and air. The thermal degradation behavior was investigated by evolved gas analysis, using coupled TG-FTIR technique. The kinetic parameters of the degradation process were determined both by isoconversional methods of Friedman and Ozawa-Flynn-Wall as well as by model fitting multivariate non-linear regression method. It was observed that the thermal stability of the poly(urethane-siloxane) thermosets depends on employed diisocyanate. The best fit of the f(alpha) function with the experimental data was found for two-step degradation mechanism. Successive stages of thermal decomposition occurred by diffusion and by the expanded Prout-Tompkins model, respectively. (C) 2014 Elsevier B.V. All rights reserved.