FURTHER-STUDIES ON THE THERMAL-DECOMPOSITION OF AIBN IMPLICATIONS CONCERNING THE MECHANISM OF TERMINATION IN METHACRYLONITRILE POLYMERIZATION

The products formed during thermal decomposition of AIBN-alpha-C-13 at 60-degrees in benzene and dimethyl sulphoxide have been identified and quantified by C-13-NMR. Analysis of the oligomeric products demonstrates that there is selectivity in the reaction of oligo(methacrylonitrile) radicals (5) with cyanoisopropyl radicals (1). There is a marked preference for C-N coupling over C-C coupling and the major product observed results from combination of the nitrogen of 5 with the carbon of 1. The reaction kinetics of AIBN decomposition and product formation have been analysed to yield absolute rate constants (60-degrees, benzene) for ketenimine decomposition and for the addition of 1 to methacrylonitrile. The implications of our findings are discussed with respect to the kinetics and mechanism of methacrylonitrile and other polymerizations.