Syndiospecific Polymerization of Propene Promoted by Bis(salicylaldiminato)titanium Catalysts: Regiochemistry of Monomer Insertion and Polymerization Mechanism

Abstract

Syndiotactic polypropylene samples were synthesized under proper conditions using homogeneous catalytic systems based on bis(iminophenoxy)Ti(IV) derivatives and methylaluminoxane. 13C NMR analysis of the natural abundance end groups suggests that the regiospecificity of propene insertion during the propagation is prevailingly 2,1, although 1,2 insertion is favored in the initiation step. A copolymer of propene with a small amount of 1-13C-ethene was also prepared with one of the title catalysts, and its stereochemical structure was analyzed by NMR, confirming 2,1 monomer insertion as the main mode of propagation.