Ethylene-1,2-cyclopentane random copolymers from cyclocopolymerization of ethylene/1,3-butadiene

Crystalline methylene-1,2-cyclopentane (E-1,2CP) random copolymers, containing up to 15% of cyclic units, are obtained in high yields by copolymerization of ethylene and 1,3-butadiene in the presence of rac-[CH2(3-methyl-1-indenyl)2]ZrCl2/MAO catalyst. The highly selective formation of trans methylene- 1,2-cyclopentane units occurs by an intramolecular insertion of the double bond pendant from polymeril chain after an unusual primary vinyl insertion of 1,3-butadiene. Thermal properties and structure of E-1,2CP copolymers, as function of 1,2-cyclopentane molar content, are analyzed and compared with those of other ethylene copolymers. The variation in melting temperature and crystallinity observed in E-1,2CP copolymers is consistent with that observed for ethylene copolymers with comonomers bulkier than propylene. Moreover, the 1,2-cyclopentane units, as well as comonomers bulkier than propylene, cause only slight deformations of polyethylene orthorhombic unit cell parameters. These data are rationalized by assuming that 1,2-cyclopentane units, are confined in amorphous phase, while the polyethylene crystalline phase remains pure.