G-values for scission and crosslinking on γ-radiolysis of Ultem at 303 K

The radiation chemical yields G(S) and G(X) for H-linking and Y-linking models for Ultem have been calculated from molecular weight analysis by gel permeation chromatography. These G-values have been compared with the G-values obtained from analysis of soluble fractions above the gel dose, which have been reported in previous works. An analysis of the molecular weight data in terms of H-linking and Y-linking mechanisms yielded values of G(S_H) = 1.0 × 10^-3 and G(H) = 6.0 × 10^-3 and G(S_Y) = 1.3 × 10^-2 and G(Y) = 1.8 × 10^-2. The corresponding values obtained from the solubility data were G(S_H) = 0.53 × 10^-2, G(H) = 1.39 × 10^-2, G(S_Y) = 4.2 × 10^-2 and G(Y) = 4.6 × 10^-2. The origin of the disagreement between the molecular weight and solubility values is not clear, but it could arise as a result of observed microgel formation below the reported gel dose of 0.13 MGy. Whether the crosslink mechanism proceeds by an H-linking or Y-linking process is also unclear and will require direct observation of the crosslinking structures.