Polymerization of 4-methyl-1,3-pentadiene with catalysts based on cyclopentadienyl titanium chlorides. Effect of anti-syn isomerism of the allylic group on chemoselectivity and the role of backbiting coordination in 1,3-diene polymerization

Homopolymerization of 4-methyl-1,3-pentadiene (MP) and copolymerization of 4-methyl-1,3-pentadiene with alkenes (ethylene, 1-pentene, 4-methyl-1-pentene) were performed to investigate the effect of the so-called backbiting coordination on the chemoselectivity of 1,3-diene polymerization. Three homogeneous catalyst systems were used: CpTiCl3-MAO, Cp2TiCl2-MAO and Cp2TiCl-MAO. Backbiting coordination is possible with the first catalyst, but not with the other two. The three catalysts gave similar results, which indicates that backbiting has no effect on the polymerization chemoselectivity, contrary to what has been reported in recent literature. An interpretation is presented for the formation of 1,4 units in MP/alkene copolymers. This interpretation is based on the fact that allyl groups have predominantly a syn configuration in MP homopolymerization, whereas allyl groups of anti configuration are formed in MP/alkene copolymerization. The role of backbiting in diene polymerization is discussed.