Room temperature living cationic polymerization of styrene with HX-styrenic monomer adduct/FeCl 3 systems in the presence of tetrabutylammonium halide and tetraalkylphosphonium bromide salts

Abstract

Living cationic polymerization of styrene was achieved with a series of initiating systems consisting of a HX-styrenic monomer adduct (X = Br, Cl) and ferric chloride (FeCl 3) in conjunction with added salts such as tetrabutylammonium halides ( nBu 4N +Y −; Y − = Br −, Cl −, I −) or tetraalkylphosphonium bromides [ nR′ 4PBr; R′ = CH 3CH 2–, CH 3(CH 2) 2CH 2–, CH 3(CH 2) 6CH 2–] or tetraphenylphosphonium bromide [(C 6H 5) 4PBr] in dichloromethane (CH 2Cl 2) and in toluene. Comparison of the molecular weight distributions (MWDs) of the polystyrenes prepared at different temperatures (e.g., −25 °C, 0 °C and 25 °C) showed that the polymerization is better controlled at ambient temperature (25 °C). The polymerization was almost instantaneous (completed within 1 min) and quantitative (yield ∼100%) in CH 2Cl 2. In CH 2Cl 2, polystyrenes with moderately narrow ( M w/ M n ∼ 1.33–1.40) and broad ( M w/ M n ∼ 1.5–2.4) MWDs were obtained respectively with and without nBu 4N +Y −. However, in toluene, the MWDs of the polystyrenes obtained respectively with and without nBu 4N +Y −/ nR′ 4P +Br − were moderately narrow ( M w/ M n = 1.33–1.5) and extremely narrow ( M w/ M n = 1.05–1.17). Livingness of this polymerization in CH 2Cl 2 was confirmed via monomer-addition experiment as well as from the study of molecular weights of obtained polystyrenes prepared simply by varying monomer to initiator ratio. A possible mechanistic pathway for this polymerization was suggested based on the results of the 1H NMR spectroscopic analysis of the model reactions as well as the end group analysis of the obtained polymer.