Crystalline structure were studied on both block and random propyleneethylene copolymer fractions, which were obtained by temperature rising elution fractionation. The peak characteristic of a-polypropylene (PP) was observed for all fractions, except the fraction eluted at room temperature. A characteristic peak of polyethylene crystals [i.e., (200) planes] was observed in some fractions, indicating the existence of long ethylene sequence in these fractions. This is in accordance with the analysis from Fourier transform infrared spectroscopy and 13 C-NMR. The g-form crystal of PP was observed in these copolymer fractions at atmospheric pressure. It is suggested that the insertion of comonomer into the isotactic PP chain makes the crystallizable sequences sufficiently short and produces the g-form crystal.

ABSTRACT:The crystallization, melting behavior, and morphology of a low ethylene content block propylene-ethylene copolymer (BPP) and a high-density polyethylene (HDPE) blend were studied. It was found that the existence of ethylene-propylene rubber (EPR) in BPP has more influence on the crystallization of HDPE than on that of PP. This leads to the decreasing of the melting temperature of the HDPE component in the blends. It is suggested that the EPR component in BPP shifted to the HDPE component during the blending process. The crystallinity of the HDPE phase in the blends decreased with increasing BPP content. The morphology of these blends was studied by polarized light microscopy (PLM) and SEM. For a BPP-rich blend, it was observed that the HDPE phase formed particles dispersed in the PP matrix. The amorphous EPR chains may penetrate into HDPE particles to form a transition layer.

ABSTRACT:Multiple melting peaks phenomena have been investigated in terms of compositional heterogeneity, crystallization temperature, cooling rate, heating rate, annealing and crystal structure for low ethylene content block and random propylene-ethylene copolymers. The experimental results suggested that the compositional heterogeneity and crystal morphology play an important role in the cause of multiple melting behavior.

Dynamic mechanical behavior of low ethylene content propylene-ethylene copolymers was studied. It was found that there exists ethylene-propylene rubber component in the block copolymer, which is accordance with the component analysis. It is suggested that it is because of the existence of the ethylene-propylene rubber component that the block copolymer exhibits high impact strength. The relaxation temperature shifted to lower temperature for copolymers compared with homopolymer, and the damping peak was broadened by copolymerization, consistent with the increased chemical heterogeneity of the copolymers. Effects of thermal history and frequency on the relaxations were studied. The activation enthalpy for relaxation was determined.