Structure, morphology, and crystallization of a random ethylene-propylene copolymer

The structure, morphology, and crystallization behavior of a random ethylene-propylene copolymer, containing 2 wt % ethylene sequences, are analyzed and compared with those of a plain polypropylene sample by means of optical and scanning microscopy, wide-angle X-ray scattering, and calorimetry. For the copolymer, different polymorphs (alpha, gamma and smectic modifications) and morphologies can be obtained through changes in the crystallization and annealing conditions. The analysis of the structural results Suggests that the gamma phase of isotactic polypropylene can be generated for high molecular mass samples with drastic decreases in the undercooling. The spherulite growth rate (G) data, in conjunction with the crystallization temperatures (T-c's), are obtained with the procedure suggested by Chung and Chen and modified by Silvestre et al. The results demonstrate that the presence of ethylene sequences reduces G at a given value of T-c. It is hypothesized that at atmospheric pressure and T-c = 110-128 degreesC, the different polymorphs have different crystallization growth rates (G(gamma) < G(alpha) < G(beta)). (C) 2003 Wiley Periodicals, Inc.