Investigations into the AIBN initiation steps in the free radical polymerisation of acrylonitrile by the aminoxyl trapping technique

A modification of the radical trapping technique employing the stable nitroxide 1,1,3,3-tetramethyl-2,3-dihydro- 1H-isoindol-2-yloxyl, has been used to study the reaction of cyanoisopropyl radicals with acrylonitrile. By keeping the concentration of the aminoxyl radical very low (strategically added via a syringe pump), the addition of acrylonitrile to cyanoisopropyl radicals becomes competitive with radical trapping. Thus, sufficient quantities of alkoxyamines produced by the trapping of 'second generation' carbon-centred radicals (cyanoisopropyl plus one monomer unit), and even 'third generation' carbon-centred radicals were obtained for identification by HPLC / MS techniques. Trapping by traces of adventitious oxygen was also competitive and the various peroxy radicals thus formed, underwent addition to acrylonitrile followed by further reaction or trapping by the aminoxyl.