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RESEARCH PRODUCT

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

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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 (α, γ 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 γ 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 (Tc'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 Tc. It is hypothesized that at atmospheric pressure and Tc = 110–128 °C, the different polymorphs have different crystallization growth rates (Gγ < Gα < Gβ). © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 493–500, 2003