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

Structure, morphology and crystallization behaviour of a random ethylene-propylene copolymer, containing 2% in weight of 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 (alfa, gamma and smectic modification) and morphologies can be obtained changing crystallization and annealing conditions. The analysis of the structural results suggests that gamma-phase of isotactic polypropylene (iPP) could be generated for high molecular mass samples decreasing drastically the undercooling. The spherulite growth rate data in dependence on Tc are obtained by using the procedure suggested by Chung and Chen and modified by Silvestre et al. The results demonstrate that the presence of ethylene sequences decreases the spherulite growth rate, G, at given Tc. It is hypothesized that at atmospheric pressure and Tc, ranging between 110-128°C, the different polymorphs have different crystallization growth rate and in particular Ggamma < Galfa < Gbeta.