Macromolecules, Vol.32, No.5, 1348-1355, 1999
Copolymerization of propene and nonconjugated diene involving intramolecular cyclization with metallocene/methylaluminoxane
Copolymerizations of propene with 1,5-hexadiene and 1,7-octadiene were carried out with isospecific rac-dimethylsilylenebis(indenyl)zirconium dichloride (1) and syndiospecific diphenylmethylene(cyclopentadienyl) (9-fluorenyl)zirconium dichloride (2), combined with methylaluminoxane. Microstructures of the copolymers were determined by H-1 NMR, C-13 NMR, and DEFT (distortionless enhancement of polarization transfer) spectroscopies. Incorporation of nonconjugated dienes in the copolymer was higher with 2 than with I. Intramolecular cycloaddition of the nonconjugated dienes proceeded regardless of the catalysts. Stereoselectivity in cycloaddition of 1,5-hexadiene was investigated based on the structures of isolated methylene-1,3-cyclopentane units. It was found that 1,5-hexadiene was inserted stereospecifically by enantiomorphic site control with both catalysts. The diastereoselectivity of the cyclization step of 1,2-inserted 1,5-hexadiene was, however, found to be independent of stereospecificity of the catalyst. The cyclization selectivity of 1,5-hexadiene copolymerization was higher than that of 1,7-octadiene copolymerization. 1 gave the copolymers with higher selective in cyclization than 2 in the propene/1,5-hexadiene copolymerization, while the opposite tendency was observed in the propene/1,7-octadiene copolymerization. Decrease of cyclization selectivity was observed with the increases of 1,1,5-hexadiene and 1,7-octadiene concentration in both copolymerizations. Propene insertion could disturb the cyclization of 1,2-inserted dienes, which declined the cyclization selectivity of the copolymers, except propene/1,5-hexadiene copolymerization with 2.
Keywords:NORBORNENE-ETHYLENE COPOLYMERS;METALLOCENE CATALYSTS;CHAINTRANSFER;ENANTIOSELECTIVE CYCLOPOLYMERIZATION;HOMOGENEOUSCYCLOPOLYMERIZATION;POLYMERIZATION CONDITIONS;TRANSITION-TEMPERATURES;OLEFIN COPOLYMERIZATION;ALUMINOXANE CATALYSTS;1;5-HEXADIENE