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

Non-hindered ansa dicyclopentadienylallyl complexes of samarium, [(CMe2C5H4 )(2)Sm(allyl)](n) and (CMe2C5H4)(2)Sm(allyl)L (L=THF or allylLi) polymerize isoprene without an aluminum cocatalyst. The polymerizations are highly st ereospecific, affording nearly quantitatively 1-4 trans polyisoprene. In th e 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 fragmen ts. In the common initiator of these three catalytic systems, the (CMe2C5H4 )(2)Sm(allyl) moiety, only one vacant site would be available. As a consequ ence of the presence of the alkyl aliphatic chain, the viscoelastic behavio ur of the branched copolymers markedly differs from that of trans 1-4 polyi soprene: an important loss of crystallinity and a dramatic decrease of the Young modulus are observed; the copolymers show elastomeric properties. (C) 2001 Elsevier Science B.V. All rights reserved.