Study on enthalpy relaxation of glassy polystyrene using Kohlrausch, Davidson-Cole and Havriliak-Negami distribution functions

•Heterogeneous kinetic model combining the exponential decay with relaxation time distribution function is used to fit the heat capacity data of polystyrene.•The shape of the calculated heat capacity peak is highly correlated to the shape of the relaxation time distribution function.•The fitting quality improved greatly when the mirror function of Kohlrausch and DC distribution functions of relaxation times are used. The heat capacity data of PS after cooling at different rates were analyzed using heterogeneous kinetic model by combining exponential decay equation with various relaxation time distribution functions instead of the conventional method of combining the stretched relaxation function with Boltzmann superposition. It is found that the shape of the calculated heat capacity peak is highly correlated to the shape of the relaxation time distribution function. The fitting quality of the Davidson-Cole distribution function is worse compared with that of Kohlrausch distribution function. When the mirror functions of Kohlrausch and Davidson-Cole are used, the fitting quality improved greatly. The result indicates that relaxation kinetic of polymer may be described better by combining appropriate relaxation time spectrum with relaxation time model. This approach affords the possibility of taking the temperature and structure dependence of Kohlrausch exponent into consideration in the kinetic study of polymer in non-isothermal relaxations.