Crystalline structure and thermal property of polyethylene and isotactic polypropylene containing cyclopentane units in the main chain

Polyethylene and isotactic polypropylene having 1,2- or 1,3-disubstituted cyclopentane structures were prepared by copolymerization of ethylene or propylene with cyclopentene (CPE) or 1,5-hexadiene (HD) using zirconocene catalysts. Effect of the cyclopentane structures on the melting point and crystalline structure of the copolymers was investigated. In the case of ethylene-based copolymers, polyethylene containing 1,3-disubstituted cyclopentane structure, poly(ethylene-co-HD), showed a lower degree of melting-point depression and decreasing crystallinity with increasing cyclopentane contents than polyethylene containing 1,2-disubstituted cyclopentane structure, poly(ethylene-co-CPE). Expansion of crystalline unit cell, especially along the a-axis, with increasing cyclopentane content was observed in the wide-angle X-ray diffraction patterns of the poly(ethylene-co-HD). The phenomenon indicated incorporation of 1,3-disubstituted cyclopentane structure in the crystalline phase of polyethylene. On the other hand, both poly(propylene-co-CPE) and poly(propylene-co-HD) showed similar profiles in the relationship between the comonomer content and the melting point or the crystallinity of the copolymers.