Crystallisation and mechanical properties of syndiotactic polystyrene

The crystallisation kinetics, the dynamic mechanical properties and the melting behaviour of syndiotactic polystyrene (sPS) were examined. The influence of the crystallisation temperature on these properties was considered. Samples were either crystallised close to the melting temperature, T _m ($\sim$270°C) or close to the glass transition temperature, T_g ($\sim$100°C).; The crystallisation of sPS was studied over the temperature range from T_g to T_m. Using transmission electron and optical microscopies, the different lamellar and spherulitic microstructures which were formed over this temperature range were correlated with the measured kinetics. The rate of crystallisation was measured isothermally using thin samples in a differential scanning calorimeter. The low temperature transformations were achieved by first quenching to the amorphous state, then reheating. It was found that to estimate the crystallisation parameters most accurately the data must be fitted simultaneously at high and low temperatures and a relatively high value for the equilibrium melting temperature (561 K) must be used. The parameters from the isothermal experiments were used to predict non-isothermal crystallisation kinetics using Nakamura's model.; The origin of multiple peaks in the melting endotherms of samples initially cooled at different rates from the melt was determined. Two of the peaks found in samples cooled at 10 C°/min were caused by melting and recrystallisation during the heating scan. Two additional peaks were due to melting of distinct populations of lamellae. Evidence of these two populations was found in the lamellar morphology.; The storage modulus of samples crystallised close to T_m and samples crystallised close to T_g differ by almost an order of magnitude above T_g. This difference was determined to be due to the lamellar morphology. The morphology was examined using transmission electron microscopy. The influence of the morphology on the mechanical properties was shown using Takayanagi's combination models. In samples crystallised at high temperatures the lamellae formed a continuous phase but in samples crystallised close to T_g the amorphous phase was continuous. The overall modulus was influenced by a constrained amorphous fraction. The increased modulus of this amorphous material was determined by including an additional parameter in the Takayanagi model.