Copolymerization of styrene with butadiene and isoprene catalyzed by the monocyclopentadienyl titanium complex Ti(eta(5)-C5H5)(eta(2)-MBMP)Cl

Polymerization of butadiene, isoprene, and styrene was investigated using the catalyst Ti(η5-C5H5)(η2-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 °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 r1 = 70 and r2 = 1.2 determined by NMR methods confirmed the blocky distribution of the monomers in the copolymer chain. The AFM of copolymers rich in styrene (xS = 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 13C 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 r1 = 18 and r2 = 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.