The influence of monomer chemistry on radical formation and secondary reactions during electron-beam polymerization

The vast majority of industrial electron-beam (EB) polymerizations are initiated via radical mechanism. Because radicals drive EB polymerization, understanding their formation and secondary reactions can provide insight into polymerization kinetics and property development. Primary and initiating radicals were quantified by measuring G(R^•) and G(M^•) , respectively, for various acrylate and methacrylate monomers. Monomer chemistry was shown to impact primary radical formation; however, increased primary radical concentration did not necessarily correlate to increased conversion. Despite exhibiting high values of G(R^•) , methacrylates achieved very little conversion and had G(M^•) values near zero. Acrylates achieved much higher G(M^•) values and rates of polymerization compared to their methacrylate counterparts. Additionally, the efficiency of primary radicals converting to initiating radicals, f(M^•) , for each acrylate monomer was shown to be a good predictor of the amount of gel fraction formed during polymerization. Understanding radical formation and secondary radical reactions can help guide the structure/processing conditions/properties relationships that are currently underdeveloped for EB reactions.