Controlled Cationic Polymerization of p-Methylstyrene in Ionic Liquid and Its Mechanism

Ionic liquid (IL) as a green solvent is entirely composed of ions; thus, it may be more than a simple solvent for ionic polymerization. Here, the cationic polymerization of p-methylstyrene (p-MeSt) initiated by 1-chloro-1-(4-methylphenyl)-ethane (p-MeStCl)/tin tetrachloride (SnCl4) was systematically studied in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bmim][NTf2]) IL at −25 °C. The results show that IL did not participate in cationic polymerization, but its ionic environment and high polarity were favorable for the polarization of initiator and monomer and facilitate the controllability. The gel permeation chromatography (GPC) trace of the poly(p-methylstyrene) (poly(p-MeSt)) changes from bimodal in dichloromethane (CH2Cl2) to unimodal in IL, and polydispersities Mw/Mn of the polymer in IL showed narrower (1.40–1.59). The reaction rate and heat release rate were milder in IL. The effects of the initiating system, Lewis acid concentration, and 2,6-di-tert-butylpyridine (DTBP) concentration on the polymerization were investigated. The controlled cationic polymerization initiated by p-MeStCl/SnCl4 was obtained. The polymerization mechanism of p-MeSt in [Bmim][NTf2] was also proposed.