1,5-hexadiene and 1,7-octadiene polymerization by linked-half titanocene catalysts and thermal stability of cycloolefin polymer containing pendant vinyl group

Abstract

We investigated the coordination polymerization of non-conjugated α,ω-dienes, specifically 1,5-hexadiene (HD) and 1,7-octadiene (OD), using linked-half titanocene catalysts. The two catalysts examined were a pentamethylcyclopentadienylamido-ligated titanocene (complex 1) and an indenylamido-ligated titanocene (complex 2), both were combined with dried modified methylaluminoxane. HD polymerization with both catalysts yielded cross-linked polymers in 24 h. Polymerization of HD with complex 1 for 5 min yielded soluble polymers with a unimodal molecular weight distribution and a cyclization selectivity of 70 %. In contrast, OD polymerization was slower than HD polymerization even though soluble polymers were obtained in 24 h as well. PolyODs with a molecular weight of more than 10 kg/mol were obtained with an approximate 1:1 ratio of cyclization to monomer-insertion whether complex 1 or 2 was used. The effect of solvents was studied, and the cyclization selectivity was found to decrease when a solvent with a low dielectric constant, i.e. hexane, was used (66 % of the pendant vinyl group). The glass-transition temperatures of polyOD were found to vary from −26 °C to −3 °C depending on its microstructure, and the melting temperature of the sample containing 73 % cyclic structure was observed to be 159 °C. Furthermore, the thermal stability of polyOD was investigated through heating experiments both in film and in solution.