Aqueous emulsion homo- and copolymerization of 1,3-dienes and styrene in the presence of Cp2TiCl2

The aqueous emulsion homopolymerizations of 1,3-butadiene and isoprene were investigated using bis-cyclopentadienyl titanium dichloride (Cp2TiCl2) as an active initiator. The copolymerizations of the same monomers with styrene were also performed. Cp2TiCl2, which has already been used for the production of atactic polystyrene, exhibited low activity in the homopolymerization of conjugated dienes, whereas better performance was obtained in copolymerization reactions. Both of the homopolymers, polybutadiene and polyisoprene, presented similar microstructures. The majority of the polymer chains were formed by 1,4-trans units and, to a lesser extent, by 1,4-cis and 1,2 (3,4 in the case of isoprene) units. All the copolymers presented a statistical distribution with atactic polystyrene sequences and 1,4-trans, 1,4-cis and 1,2 (3,4 in the case of isoprene) diene units. The copolymerization activity values and the percentage of inserted diene units were strictly correlated to the composition of the reaction mixture. The molecular weights of the co-polymers were substantially less than those detected for the styrene homopolymer and similar to those detected for polybutadiene and polyisoprene. Depending on the composition of the copolymer, the glass transition temperatures presented values between those of polystyrene and polydienes.