title: E stereoregular 1,1 and 1,3 constitutional units from 1,3-butadiene in copolymerizations catalyzed by a highly hindered c(2) symmetric metallocene.
abstract: Unprecedented 1,1 and 1,3 constitutional units from 1,3-butadiene, both presenting only the E configuration of the double bond, have been achieved by copolymerization with ethene, conducted at high temperature and low ethene concentration, when catalyzed by a highly hindered C(2) symmetric metallocene. Ethene/butadiene copolymerizations by this catalyst generally lead to prevailing methylene-1,2-cyclopropane units from butadiene. Polymer microstructures obtained for different comonomer concentrations clearly indicate that the rate-determining step leading to cyclopropanation involves ethene, while that leading to 1,1 and 1,3 constitutional units does not. A general copolymerization scheme and a molecular modeling study of the cyclopropanation reaction are presented. Molecular modeling also indicates that the E stereoselectivity for 1,1 and 1,3 constitutional units can be rationalized, in the assumption that an allyl isomerization of the terminal of the growing chain would occur.
authors.affiliation: Università di Salerno, Dipartimento di Chimica Via S. Allende, I-84081 Baronissi Salerno, Italy.
authors.forename: Pasquale
authors.initials: P
authors.lastname: Longo
authors.forename: Stefania
authors.initials: S
authors.lastname: Pragliola
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Milano
authors.forename: Gaetano
authors.initials: G
authors.lastname: Guerra