Organoborate Acids as Initiators for Cationic Polymerization of Styrene in an Ionic Liquid Medium

A controlled cationic polymerization of styrene has been achieved using bisoxalatoboric acid (HBOB) as an initiator in a room temperature ionic liquid (IL) under mild reaction conditions to obtain polymers of low molecular weights and narrow polydispersity. HBOB represents a relatively easily handled cationic initiator as compared to those often used in cationic polymerization reactions. The concentration of HBOB was optimized, and it was found that the molecular weights of these polymers increased with decreasing HBOB concentration. Studies were performed with different water contents in the reaction mixture to gauge the water tolerance above which the polymerization is inhibited. Experiments were also carried out with other organoborate acids, and it was found that the trend in yields followed trends in Bronsted acidity. The efficiency of different ILs as reaction solvents is also discussed.