Polymer-gel formation and reformation on irradiation of tertiary-butyl acrylate

The purpose of the present research was to provide a radiation-chemical basis for the use of tertiarybutyl acrylate gels in radio-fluorogenic dose-imaging applications (Warman et al. 2011a,b, 2013a,b). The radiation-induced polymerization of tertiary-butyl acrylate (TBA) results in the formation of a transparent gel with an optical density lower than 0.1 cm(-1) from 600 nm down to 315 nm. The fractional monomer-to-polymer conversion, C-M, determined gravimetrically, increases super-linearly with dose, D Gy. Up to C-M approximate to 40%, and over the dose rate range D'=3.5 to 49 cGy s(-1), the dose dependence is given by C-M = [1 + AC(M)]KD/root D' with K=1.43 x 10(-3) Gy(-0.5) S-0.5 and A=0.70. For D'=3.5 cGy s(-1) the average polymer size is estimated to be 1.2 x 10(5) monomer units or 17 megadalton. For C-M >= 10% the gel is quasirigid, displaying little tendency to flow on a timescale of an hour or more. After removal of monomer by evacuation, the gel can be reformed by adding a volume of monomer to the remaining polymer equal to that removed and allowing this to swell for several days. The dose and dose rate dependence of radiation-induced monomer conversion in the reformed gel show no evidence of a discontinuity caused by the intervening evacuation and reformation procedures. (C) 2013 Elsevier Ltd. All rights reserved.