Organolanthanides, catalysts for specific olefin-diene copolymerization: access to new materials

Abstract

Non-hindered ansa dicyclopentadienylallyl complexes of samarium, [(CMe 2C 5H 4) 2Sm(allyl)] n , and (CMe 2C 5H 4) 2Sm(allyl)L (L=THF or allylLi) polymerize isoprene without an aluminum cocatalyst. The polymerizations are highly stereospecific, affording nearly quantitatively 1–4 trans polyisoprene. In the presence of linear 1-olefins, copolymers are formed, with 6–10% of olefin inserted; the 1–4 trans structure of the polyisoprene chain is not altered, and only one olefin molecule is inserted between two polyisoprene fragments. In the common initiator of these three catalytic systems, the (CMe 2C 5H 4) 2Sm(allyl) moiety, only one vacant site would be available. As a consequence of the presence of the alkyl aliphatic chain, the viscoelastic behaviour of the branched copolymers markedly differs from that of trans 1–4 polyisoprene: an important loss of crystallinity and a dramatic decrease of the Young modulus are observed; the copolymers show elastomeric properties.