Thermal cross-linking of poly(vinyl methyl ether). III. Rheological kinetics of cross-linking reaction

The kinetics of the thermally activated cross-linking reaction of poly(vinyl methyl ether) (PVME) were investigated rheologically by evaluating the viscoelastic material functions such as elastic storage modulus, G″, viscous loss modulus, G″ and complex dynamic viscosity, η*, during the curing process, both isothermally and nonisothermally. The isothermal kinetics reaction was described using a phenomenological equation based on the Malkin and Kulichikhin model, which was predicated originally for the isothermal curing kinetics of thermosetting polymers followed by differential scanning calorimetery (DSC) and was found to be applicable for rheokinetic reactions as well. An excellent representation of the data was obtained using this model; the rate of the reaction was found to be second order regardless of the temperature, which is in good agreement with literature data. The temperature dependence of the cross-linking rate constant was described by an Arrhenius plot with an apparent activation energy equal to 60-62 kJ mol^-1, in reasonable agreement with the value obtained previously from the temperature dependence of gel time, t_gel. The nonisothermal kinetics reaction rate was described by a model that included the classical rate equation, the Arrhenius equation, and the time-temperature relationships. The apparent activation energy obtained nonisothermally was found to be frequency independent and equal to 72 kJ mol^-1, in very good agreement with the value obtained isothermally from the temperature dependence of t_gel in part II.