Dynamical mechanical behavior of copolymers made of styrene and methyl methacrylate: Random, alternate and diblock copolymers

The dynamics of copolymers made of styrene and methyl methacrylate and of different architecture (three diblock, two random and one alternate) have been studied using a dynamic mechanical spectroscopy technique (DMTA). The scanning calorimetric results indicate that there is only one glass transition except for two of the diblock copolymers. In addition, only one broad mechanical relaxation is observed in all the copolymers studied in this work. However, it has not been possible to build master curves for the complex Young modulus E* for the copolymers. In fact the relaxation spectra calculated from E* are bimodal. In order to describe the relaxation functions of the samples, it has been necessary to use two Kohlraush-Williams-Watts functions at each of the temperatures studied. The relaxation times of the two dynamic contributions can be described by Arrhenius laws, which is probably due to the relatively narrow temperature range for which the relaxation can be studied within the frequency range experimentally accessible. The stretching parameters increase linearly with T, which indicates that both dynamic transitions broaden as T is decreased.