Simultaneous control over the molecular weight and tacticity of poly(vinyl acetate) using a low-temperature photoinitiated RAFT process in fluoroalcohols

Abstract

A photoinitiated RAFT process in fluoroalcohols (FAs) was successfully applied to the preparation of poly(vinyl acetate) and its hydrolyzed polymer, poly(vinyl alcohol), permitting the simultaneous control over the molecular weight (MW) and tacticity. The polymerization reaction displayed living polymerization characteristics, evidenced with linear relationships between ln([M]₀/[M]) and time, and between the MW and the conversion. Polymers of higher syndiotacticity could be prepared by using the FA solvent, achieving a 62.4% racemic diad at −20 °C. The syndiotacticity of the polymer increased with increasing concentrations of FAs or with decreasing polymerization temperatures, and the dependence was stronger than the one observed in conventional radical polymerization reactions due to the slower RAFT process. Furthermore, by performing a sequential polymerization reaction involving the high-temperature reaction in the bulk state and the low-temperature reaction in the FAs, stereoblock copolymers of poly(vinyl alcohol) could be obtained.