Stereoselective cationic polymerization of vinyl ethers by easily and finely tunable titanium complexes prepared from tartrate-derived diols: isospecific polymerization and recognition of chiral side chains

Abstract

Titanium complexes of α,α,α′,α′-tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL), derived from naturally abundant tartaric acid, were demonstrated to function as highly effective catalysts for the stereoselective cationic polymerization of vinyl ethers (VEs). Isotactic poly(isobutyl VE) (m = 90%) was generated via polymerization using an initiating system prepared by simply mixing TADDOL, TiCl₄, and isobutyl VE monomer. High isotacticity was also attained in the polymerization of other VEs, such as n-propyl VE (m = 83%) and 2-phenylethyl VE (m = 94%). In addition, the chiral titanium TADDOLate catalyst recognized chiral pendant groups on VEs such as bornyl VE and menthyl VE. Polymers with dramatically different stereoregularities were obtained from (R,R)- and (S,S)-TADDOLs, which indicates that the chiral pendant groups of the VEs can induce “match/mismatch” interactions with the chiral catalysts in this cationic polymerization. The titanium center, the TADDOL substituents, and the monomer structure were most likely responsible for the stereocontrol. These well-defined titanium TADDOLates, which can be prepared easily and economically with various substituents, will provide a platform for designing stereoselective cationic polymerization catalysts.