Polymerization of acrylonitrile by use of potassium alkoxides

Abstract

The heterogeneous anionic polymerization of acrylonitrile in petroleum ether by potassium alcoholic alkoxide solutions at low temperature was studied. Alkoxides of the more electropositive metal were more active catalysts, ROK > RONa. Increasing amount of alcohol in the polymerization mixture up to a limit, had an activating effect. Yield of polymer increased with catalyst concentration. The mechanism of the polymerization consists of initiation by direct interaction of alkoxide anion with monomer, with no cocatalyst; this is substantiated by the presence of alkoxyl groups in the polymers and by the existence of steric effects of bulkyl alkoxide groups. Termination is by proton abstraction from alcohol. In accordance with this, the degree of polymerization was found to be independent of catalyst concentration, directly proportional to monomer, and inversely to alcohol concentrations, according to the equation, DP = kp[M]/kt[ROH]. Plot of DP versus monomer and the reciprocal of the alcohol concentrations gave values for kp/kt of about 35. All polymerizations showed an induction period with the following regularities. It increased with increasing concentration of alcohol and with lowering of temperature, and decreased with increasing catalyst and monomer concentrations and was smaller with the more active potassium catalysts. Induction periods seem to originate from the competing side-reaction of cyanoethylation, the initiation step of the polymerization being identical with the first step (RO− addition) in the cyanoethylation reaction. Cyanoethylation products were isolated from polymerization mixtures.