Copolymerization of Ethylene with α-Olefins Containing Various Substituents Catalyzed by Half-Titanocenes: Factors Affecting the Monomer Reactivities

Abstract

Ethylene copolymerizations with various pentenes [1-pentene, 4-methyl-1-pentene (4M1P), 3-methyl-1-pentene (3M1P), 4,4-dimethyl-1-pentene (NHEP)] using Cp*TiCl2(O-2,6-iPr2C6H3) (1), CpTiCl2(N═ CtBu2) (2), [Me2Si(C5Me4)(NtBu)]TiCl2 (4) − MAO catalyst systems have been explored. Both 1 and 2 exhibited high catalytic activities affording high molecular weight copolymers with unimodal molecular weight distributions; the rErC values (rE = kEE/kEC; E = ethylene; C = comonomer) by 1 were small, suggesting that the monomer incorporations were rather alternating, whereas the copolymerization by 4 proceeded in a random manner (rErC = ca. 1) except the copolymerization with 3M1P. 1 exhibited remarkable both catalytic activities and 3M1P incorporation in the ethylene/3M1P copolymerization, and the rE value (8.73) was much smaller than that by 4 (92), 2 (28.3). Both 1 and 4 showed better NHEP incorporations than 2 in the ethylene/NHEP copolymerization, and the rather large rE value by 2 (6.77) compared to those by 1 (2.58−2.94) was also obtained in the copolymerization with 4M1P. These results clearly indicate that the monomer reactivities (rE values) are influenced not only by the substituent in the olefins, but also by the nature of the catalytically active species (structure, and ligand set employed). Both 1 and 2 also exhibited notable catalytic activities in the copolymerization of ethylene with 1-dodecene, 1-hexadecene, affording high molecular weight copolymers with unimodal molecular weight distributions. No notable differences toward the rE values by 1,2,4 were seen, although the values were slightly affected by both the steric bulk of olefins (linear branching) and the catalyst structure employed.