Electron-beam initiated crosslinking in poly(N-isopropylacrylamide) aqueous solution

The reactions between the OH, H and e(aq)(-) transients of water radiolysis and a linear poly(N-isopropylacrylamide) were identified by the spectral and kinetic properties of intermediates. The radical responsible for crosslink formation is the isopropyl-centered radical that forms mainly in OH radical attack on the polymer. Below pH 3 this radical undergoes reversible protonation with pK(a) approximate to 2.1. The radical decay is composed of fast and slow parts. The initial fast decay is attributed to intramolecular reactions of radicals on the same chain (loop formation), the following slow decay to competition between further intramolecular and intermolecular (H-type crosslinks) termination processes. The differences in the network formation during irradiation of aqueous monomer and polymer solutions are discussed. (C) 2003 Elsevier Ltd. All rights reserved.