Chain Termination and Transfer Reactions in the Acrylate Polymerization by a Monometallic Chiral Zirconocenium Catalyst System

Abstract

Unlike the living polymerization of methacrylates and acrylamides by the monometallic propagating, chiral ansa-zirconocenium ester enolate rac-(EBI)Zr+(THF)[OC(OiPr)CMe2][MeB(C6F5)3]- [1; EBI = C2H4(Ind)2], the polymerization of acrylates such as n-butyl acrylate (n-BA) by 1 proceeds in an uncontrolled fashion to only moderate monomer conversions, producing poly(n-BA) with three types of chain structuresone major linear and two minor cyclic β-ketoester-terminated poly(n-BA) chains. The combined polymerization, chain structure, and model reaction studies have shown the presence of substantial chain termination processes in this system that prevent it from achieving high monomer conversions and producing only the living linear chain structure. The proposed overall three-step mechanism, involving isomerization of the cyclic reactive intermediate, backbiting cyclization to eliminate an alcohol, and chain termination by the alcohol, explains the catalyst deactivation pathways as well as the resulting polymer c...