Unveiling the Mechanistic Role of Lewis Acidic Ionic Liquids in Styrene Polymerization

This work describes the use of a series of Lewis acids supported in different ionic liquids (ILs), based on an imidazolium cation, as catalysts for the cationic polymerization of styrene. The influence of these ILs, the effect of Lewis acids, temperature, catalyst concentration, and the presence of organic solvents were investigated to evaluate the best conditions for polymerization. These catalytic systems were effective to polymerize styrene in the temperature range of 50–90 °C, obtaining quantitative conversions in the presence of ILs in polymerization catalyzed by small amounts of Lewis acid. It was possible to synthesize polymers with wide ranges of number-average molar mass, in the range of 200,000–600 g mol–1, with a wide range of molar-mass dispersity, ranging from 1.43 to 4.67, and glass transition temperatures in the range of 40–71 °C by varying the catalytic system and/or the synthesis temperature. The polymerization mechanism was investigated by ESI-MS(/MS) in positive mode with highly elucidative results. Tailored polystyrenes were successfully synthesized due to the fundamental properties of task-specific ILs, paving the way for the industrial application of catalyst systems based on ILs/Lewis acids.