Polymerization of acrylonitrile by electron transfer catalysts

Abstract

AbstractThe heterogeneous polymerization of acrylonitrile in tetrahydrofuran by chain transfer catalysts: monosodium anthracene, disodium anthracene, sodium naphthalene, monolithium anthracene, and lithium naphthalene was investigated. The free radical formed in the initiation was found to participate in the polymerization process only in the case of lithium naphthalene at low catalyst concentrations. Also, block copolymerization with styrene, which is more reactive in free radical polymerization than acrylonitrile and less in anionic, succeeded only with lithium naphthalene. The absence of dimerization of the free radicals is mainly due to their occlusion caused by the high rate of the anionic polymerization of acrylonitrile and the low polymerization temperature, and in the case of the anthracene catalysts also due to inhibition of the free radical dimerization by the liberated anthracene. The mechanism of the termination of the polymerization was found to depend on the catalyst concentration and the ratio [MI]/[C]. At high catalyst concentrations and relatively low [M]/[C] values, termination was by chain transfer to the monomer, as can be seen from the independence of the molecular weights on both monomer and catalyst concentrations. At low catalyst concentrations and relatively high [M]/[C] values, the molecular weights were found to increase with monomer concentration and decrease with catalyst concentration. This was found to be due to the anionic mechanism of the polymerization, and the results are similar to those obtained in a typical anionic polymerization of acrylonitrile with butyllithium.