Styrene/1,3-butadiene copolymerization by C2-symmetric group 4 metallocenes based catalysts

C-2-symmetric group 4 metallocenes based catalysts (rac-[CH2(3-tert-butyl-1-indenyl)(2)]ZrCl2 (1), rac-[CH2(1-indenyl)(2)]ZrCl2 (2) and rac-[CH2(3-tert-butyl-1-indenyl)(2)]TiCl2 (3)) are able to copolymerize styrene and 1,3-butadiene, to give products with high molecular weight. In agreement with symmetry properties of metallocene precatalysts, styrene homosequences are in isotactic arrangements. Full determination of microstructure of copolymers was obtained by C-13 NMR and FTIR analysis and it reveals that insertion of butadiene on styrene chain-end happens prevailingly with 1,4-trans configuration. In the butadiene homosequences, using zirconocene-based catalysts, the 1,4-trans arrangement is favored over 1,4-cis, but the latter is prevailing in the presence of titanocene (3). Diad composition analysis of the copolymers makes possible to estimate the reactivity ratios of copolymerization: zirconocenes (1) and (2) produced copolymers having r(1) X r(2) = 0.5 and 3.0, respectively (where 1 refers to styrene and 2 to butadiene); while titanocene (3) gave tendencially blocky styrene-butadiene copolymers (r(1) x r(2) = 8.5). The copolymers do not exhibit crystallinity, even when they contain a high molar fraction of styrene. Probably, comonomer homosequences are too short to crystallize (n(s) = 16, in the copolymer at highest styrene molar fraction). (c) 2008 Wiley Periodicals, Inc.