Dual control of stereoregularity and molecular weight in cationic polymerization of vinyl ether by tunable TADDOLs/TiCl₄ initiating systems

The effects of aryl substituents on alpha,alpha,alpha',alpha'-tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL) ligands were investigated to develop a TADDOL/TiCl4 system that simultaneously controls the stereoregularity and molecular weight of poly(isobutyl vinyl ether). Substituents were appropriately designed to generate polymers with relatively high m values (80-90%) and narrow molecular weight distributions (M-w/M-n = 1.1-1.4) at 0 C-degrees and -78 C-degrees. The steric and electronic effects of TADDOL substituents on the stereoregularity and molecular weight were investigated. Interestingly, conventional fast equilibrium between the dormant C-Cl bonds and active species was likely absent at -78 C-degrees, while the polymerization was mediated by long-lived species, resulting in a linear increase in molecular weights with monomer consumption. This study provides significant insight for the development of high-performance polymerization catalysts through which multiple polymer structures can be simultaneously controlled.