Primary reactions in the electron-induced polymerization of acrylates

Abstract

Using electron pulse radiolysis with optical detection the mechanism of the polymerization of tripropyleneglycol diacrylate (TPGDA) induced by electron-irradiation was studied at room temperature. The dose per pulse was 50 or 130 Gy corresponding to the electron pulse lengths of 5 and 15 ns, respectively. Short-lived transients, such as TPGDA radical cations and radical anions as well as different types of radicals were observed in neat TPGDA. The reactions of the different ions were studied separately in solutions of TPGDA in tetrahydrofuran and in n-butylchloride. TPGDA cations produced by charge transfer from n-butylchloride primary cations undergo both rapid deprotonation and ion-molecule reactions with TPGDA. Deprotonation leads to TPGDA vinyl-type radicals. In tetrahydrofuran TPGDA radical anions are produced by reaction of the solvated electron with the acrylate. Fast dimerization of the anions is observed. Proton abstraction from the solvent leads to alkyl-type radicals. Addition of the different radicals to TPGDA leads to the chain start of the radical polymerization. An upper bound of 10 5 dm 3mol −1s −1 was estimated for the starting reaction. In the presence of oxygen the formation of peroxyl radicals is observed and the polymerization is inhibited.