Copolymerization of styrene with butadiene and isoprene catalyzed by the monocyclopentadienyl titanium complex Ti(η5-C5H5)(η2-MBMP)Cl

Polymerization of butadiene, isoprene, and styrene was investigated using the catalyst Ti(eta(5)-C5H5)-(eta(2)-MBMP)Cl (1) (MBMP = 2,2'-methylenebis(6-tert-butyl-4-methylphenoxo)) activated with methylaluminoxane (MAO). Syndiotactic polystyrene and cis-1,4-polybutadiene were obtained at 50 degrees C, similarly to other monocyclopentadienyl titanium catalysts previously reported. On the contrary, the 1/MAO catalyst resulted extremely active in isoprene polymerization, producing polymers with mainly cis-1,4 structure and containing head-to-head and tail-to-tail enchainments of the monomer units in a molar concentration of 21.5%. Binary copolymerization of styrene with butadiene yielded block copolymers containing segments of cis-1,4-polybutadiene and crystalline syndiotactic polystyrene. The reactivity ratios r(1) = 70 and r(2) = 1.2 determined by NMR methods confirmed the blocky distribution of the monomers in the copolymer chain. The AFM of copolymers rich in styrene (x(s) = 0.77-0.81) showed a microphase separation of polybutadiene domains in micrometric scale (average radius 800 nm). Novel copolymers of styrene with isoprene were synthesized using the 1/MAO catalyst. The C-13 NMR chemical shifts of the carbon atoms diagnostic of the different monomer diads and triads were predicted and assigned using properly calculated additive shift factors. The reactivity ratios r(1) = 18 and r(2) = 0.3 were evaluated by means of NMR methods. Despite the syndiotactic arrangement of the styrene homosequences, the styrene-co-isoprene polymers are completely soluble in organic solvents and completely amorphous also at high styrene concentration.