Poly(methyl methacrylate) and poly(methyl methacrylate–co-maleic anhydride) were prepared by free-radical, bulk polymerization using 0.005 mole % benzoyl peroxide as an initiator at 50 °C for 24 h. The resulting transparent cylinders were cut in a lathe into disks of 14-mm diameter and 2.2-mm thickness. Samples were also prepared in the form of thin slabs of 14×2×1 mm3. Subsequently, they were irradiated by γ rays at the level of 2–12 Mrad and their molecular weight distribution was determined by gel permeation chromatography. Changes in their structure before and after irradiation were determined by infrared spectroscopy. Their sensitivity values Gs and solubility characteristics in various solvents were determined. Planar and radial dissolution studies were performed in pure methyl ethyl ketone or ethanol at 26 °C. The positions of the solvent/gel and gel/glassy fronts were followed as functions of time. The results were correlated with the pseudosteady-state solutions of a new mathematical model incorporating the simultaneous effects of swelling and dissolution of the polymers.
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Parsonage et al. (1987) studied this question.