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†
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.