Effect of the particle size of the TiCl4-Ali-Bu3 catalyst on the contribution from mono- and bimetallic active sites to the polymerization of isoprene

Abstract

The interaction between the coordinatively unsaturated surface of ß-TiCl₃ particles and a liquid phase in the TiCl₄-Ali-Bu₃ catalyst is responsible for the final particle size and the regularities of isoprene polymerization. The correlations of the catalyst activity and the molecular characteristics of polyisoprene with catalyst particle size in the course of catalyst formation and reactivation are indicative of the occurrence of two groups of active sites. “Surface” active sites correspond to the monometallic Cossee model, and they are characterized by low activity and low 1,4-cis specificity in the polymerization of isoprene. “Colloid” active sites have a bimetallic structure and produce polyisoprene at a high rate; the concentration of 1,4-cis units in the resulting polyisoprene is as high as 97%. The contribution from the colloid active sites to the polymerization of isoprene increases with the particle size of ß-TiCl₃.