Allylthioketone Mediating Radical Polymerization of Styrene

Abstract

By combination of high trapping radical efficiency of thioketone with resonance of allylic radicals, a novel mediated agent, 1,3,3‐triphenylprop‐2‐ene‐1‐thione (TPPT) is successfully synthesized. The results of studying TPPT‐mediated radical polymerization of styrene (St) respectively at 70 °C and 100 °C reveal that at 70 °C, the monomer conversion is very low (less than 5%), the molecular weights do not change obviously with the monomer conversion, and their molecular weights are also low. However, the polymerization at 100 °C displays first‐order kinetics and a linear increase of the molecular weight with conversion. Several methods are used to study polymerization mechanisms and the results are interesting. The TPPT can efficiently capture the growing PS radicals to form PS‐TPPT radicals, this highly stable radical can be cross‐terminated by the primary radical R• (or the growing PS radicals) to form PS‐TPPT‐R (or PS‐TPPT‐PS), but this termination reaction is irreversible, and the dormant PS‐TPPT‐PS chains cannot be cleaved to regenerate the propagating radicals in the polymerization at 70 °C. However, the growing PS radical can be regenerated from the dormant chains at 100 °C, and the factors influencing the polymerization of St are studied.