Role of Stereochemistry in Diffusion of Polypropylene Melts: Comparison of Simulation and Experiment

摘要

We have conducted pulsed-gradient spin-echo NMR and corresponding dynamical Monte Carlo simulations to determine if the ratio of Monte Carlo steps to real time is maintained for polypropylenes of different probability of meso diad: P_m = 0.02, 0.23 and 0.89. We find that isotactic polypropylene has a different scaling ratio than syndiotactic and atactic polypropylene. While molecular weight effects are easy to discern, the stereochemical effect may be complicated by polydispersity, since the isotactic sample is more polydisperse than the other samples. The significance of stereochemistry and polydispersity when comparing simulation to experiment with realistic vinyl polymers is discussed.