Copolymerization of 1,3-butadiene and isoprene with cobalt dichloride/methylaluminoxane in the presence of triphenylphosphine

The homopolymerization and copolymerization of 1,3-butadiene and isoprene were achieved at 0 degreesC with cobalt dichloride in combination with methylaluminoxane and triphenylphosphine (Ph3P). For 1,3-butadiene, highly cis-specific and 1,2-syndiospecific polymerization proceeded in the absence or presence of Ph3P, respectively, although the activity with Ph3P was much higher than that without Ph3P. Only a trace of the polymer was, however, obtained in isoprene polymerization when Ph3P had been added. For copolymerization, the polymer yield in the presence of Ph3P was about three times higher than that in its absence. Copolymerization in the presence of Ph3P was, therefore, investigated in more detail. Unimodal gel permeation chromatography elution curves with narrower polydispersity (weight-average molecular weight/number-average molecular weight approximate to 1.5) indicated that the propagation reaction proceeded by single-site active species. Both the yield and molecular weight of the copolymer decreased with an increasing amount of isoprene in the feed, and this was followed by an increase in the isoprene content in the copolymer. The monomer reactivity ratios, r(1) (1,3-butadiene) and r(2) (isoprene), were estimated to be 2.8 and 0.15, respectively. Although the 1,3-butadiene content in the copolymer was strongly dependent on the comonomer composition in the feed, the ratio of 1,2-inserted units to 1,4-inserted units of 1,3-butadiene was constant. Concerning the isoprene unit, the percentage of 1,2- and 3,4-inserted units was increased at the expense of 1,4-inserted units with an increasing isoprene content in the feed. (C) 2002 Wiley Periodicals, Inc.