NMR spectroscopic study of side reactions in anionic polymerization of acrylonitrile

Abstract

An NMR study was conducted on the mechanisms of side reactions in anionic polymerization of acrylonitrile (AN) with di-n-hexylmagnesium as an initiator in mixed-xylene at 25°C. In the initiation step the metalation of AN monomer leads to deactivation of the initiator. In the propagation stage both chain transfer to an α-proton in propagating chain and metalation of monomer proceed in parallel with addition reaction of the AN monomer to the propagating chain. The former two reactions result in 1) formation of branching structures and 2) deactivation of active site, respectively. Some new NMR peaks resulting from above side reactions, which did not appear in 13C NMR spectra of radically prepared PAN, were assigned. According to the assignments in this work, the number-average molecular weight, Mn (330–5600) and branching density, which means the number of branching per 100 repeating units, were estimated for acetone-soluble or acetone-insoluble products. © 1993, The Society of Polymer Science, Japan. All rights reserved.