Radical formation in electron‐irradiated acrylates studied by pulse radiolysis and electron paramagnetic resonance

Electron pulse radiolysis with optical and conductometric detection as well as low‐temperature electron paramagnetic resonance (EPR) were used to study the mechanism of electron‐irradiation induced polymerisation and cross‐linking of acrylates such as triethyleneglycol (TPGDA) and butandiol (BDDA) diacrylate. Irradiation of acrylates with fast electrons generates radical cations and anions that rapidly transform to radicals. Using butyl chloride or tetrahydrofuran and water as solvents cationic and anionic pathways of radical formation were studied separately. Acrylate radical cations either deprotonate forming vinyl‐type radicals or generate covalently bonded or resonance stabilised dimer cations. Vinyl‐type radicals as well as dimer cations are able to initiate polymerisation. EPR results show that a structural transformation of TPGDA primary cations takes place by H‐transfer from the ester to the positively charged carbonyl group. Addition of solvated electrons to acrylates forms anions. Protonation of the anion at the carbonyl site leads to ketyl‐type radicals which are also able to initiate polymerisation. It is concluded that after electron‐irradiation of acrylates both cations as well as anions are important precursors of radicals which induce radical polymerisation and cross‐linking.