Influence of stereoerrors on the formation of helices during early stage crystallization of isotactic polyproyplene

Coarse-grained, on-lattice Monte Carlo simulations are performed to investigate the role of stereotacticity defects along an isotactic polypropylene chain on the formation of 3(1)-helices, which form the basic crystalline order within the chain. For this reason, systems with various stereoerror configurations are studied and are compared to neat isotactic polypropylene. All systems are equilibrated above the melting temperature and are cooled to lower temperatures in a stepwise manner, making sure each system is equilibrated at every temperature. Results indicate that chain ends have the lowest probability of being found in helices. Addition of a single stereoerror (mrm) decreases the probability of five repeat units' participation in helices (the repeat unit that contains the stereoerror and two nearest repeat units on both sides). The probability profile becomes more complicated when the number of stereoerrors increases, however, the results indicate that the effects of many stereoerrors can be explained by a simple addition of the effect of each stereoerror considered individually. The results also indicate that the presence of even a single stereoerror eliminates (within the temperature range studied) the transition to longer, more stable helices observed in neat isotactic polypropylene. (c) 2007 Wiley Periodicals, Inc.