Synthesis of polymer materials by low energy electron beam 2. Effects of irradiation dose on eb-cured polyurethane—acrylate gel films

Abstract

The structure and properties of the gel films obtained from the electron beam (EB) solid-state polymerization of urethane-acrylate prepolymer were investigated as functions of EB irradiation dose. The film of a prepolymer which was synthesized by the reaction of poly(butylene adipate)diol, 4, 4艂-diphenylmethane diisocyanate, and 2-hydroxyethyl acrylate, contained the crystalline phase arising from poly(butylene adipate). Spherulitic texture was observed on the gel film surfaces by scanning electron microscopy. Spherulitic size decreased drastically from 2.5 to 5 Mrad and diminished gradually from 5 to 20 Mrad. The crystallinity was reduced with increasing dose, while crystallite size decreased remarkably in the ranges of 0舑1 and 5舑15 Mrad. Since the crosslinking density of this EB-cured gel film rose steeply up to 5 Mrad but tended to increase gradually after 5 Mrad, it was assumed that these alternations at lower dose (below 5 Mrad) were due mainly to crosslinking by the terminal acryloyl double bonds, but at higher dose (above 5 Mrad), was due to the crosslinking relating to polymer backbones under EB heat damage. Such features of the gel films as functions of EB dose resulted in maximum values at 2.5 Mrad on stress at yield. © 1987 The Society of Polymer Science, Japan.