Poly(vinylphosphonate)s with Widely Tunable LCST: A Promising Alternative to Conventional Thermoresponsive Polymers

Abstract

Novel statistic copolymers of dialkyl vinylphosphonates have been synthesized via rare earth metal-mediated group transfer polymerization using easily accessible tris­(cyclopentadienyl)­ytterbium. The copolymerization parameters have been determined by activity measurements showing the formation of almost perfectly random copolymers (r1, r2 ∼ 1). Thus, the polymerization rate of vinylphosphonate GTP is mainly limited by the steric demand of growing polymer chain end. The obtained copolymers of diethyl vinylphosphonate and dimethyl or di-n-propyl vinylphosphonate show thermoresponsive properties, i.e., exhibit a tunable lower critical solution temperature following a coil–globule transition mechanism, with cloud points between 5 and 92 °C. Hereby, the LCST can be precisely adjusted by varying the comonomer composition and correlates linearly with the content of hydrophilic/hydrophobic comonomer. These thermoresponsive poly­(vinylphosphonate)­s, exhibiting a sharp and reversible phase transition, and minor environmental effects such as concentration and additives on their cloud point, are promising candidates in biomedical applications