On the mechanism of the electron-initiated curing of acrylates

Abstract

Using electron pulse radiolysis with optical detection the mechanism of the radiation induced polymerization of tripropyleneglycoldiacrylate (TPGDA) was studied in n-butylchloride (n-BuCl) solution at room temperature. Short-and long-lived transients, such as TPGDA radical cations and different types of radicals were observed.TPGDA cations produced by charge transfer from n-BuCl primary cations undergo both rapid deprotonation and ion-molecule reactions with TPGDA. Deprotonation leads to TPGDA vinyl-type radicals. As products two types of dimeric cations are observed: a covalently bonded dimer and a charge resonance stabilized structure. The covalently bonded dimer reacts with TPGDA and forms a species where excess charge and unpaired spin are separated by one molecular unit. Addition of the vinyl-type radicals to TPGDA leads to the chain start of the radical polymerization. An upper bound of 105 l·mol−1·s−1 was estimated for the starting reaction.In the presence of oxygen the formation of vinyl peroxyl radicals is observed and the polymerization is inhibited.