Reactions of Initiation and Reinitiation in Polymerization Mediated by Organoborane-Oxygen Systems

Abstract

The kinetics and mechanism of initiation and reinitiation reactions in the polymerization of methyl methacrylate mediated by the ammonia-tripropylborane-oxygen and 2-isopropyl-2 -boraadamantane- oxygen systems are studied by ESR spectroscopy using C-phenyl-N-tert-butylnitrone and 2 -methyl-2 -nitrosopropane as spin traps. It is shown that alkyl and alkoxyl radicals are the main initiating radicals and the rate of initiation is directly proportional to the concentration of oxygen. Two mechanisms of radical formation are valid in the postpolymerization of methyl methacrylate at room temperature under vacuum. The first one (which is predominant) is the decomposition of poly(methyl methacrylate)-boroxyl macromolecules, i.e., the reinitiation of polymerization; the second one (additional during the first 30 min of the process) is the decomposition of borane peroxide compounds accumulated during the stage of oxidation.