Thermal degradation studies of poly(urethane-siloxane) thermosets based on co-poly(dimethyl)(methyl, 3-glycidoxypropyl)siloxane and epoxy-terminated urethane oligomer

A series of crosslinked hybrid poly(urethane-siloxane) networks based on comb-like structure co-poly(dimethyl)(methyl, 3-glycidoxypropyl) siloxane, epoxy-terminated urethane oligomer cured with diethylenetriamine, were obtained. The samples were 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 Kissinger-Akahira-Sunose 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 the siloxane content. The first stage of degradation is associated with urethane degradation and the second with decomposition of polyoxytetramethylene and siloxane moieties. The best fit of the f(α) function with the experimental data was found for two-step degradation mechanism.