Evaluation of Cross-Linking and Scission Yields in Irradiated Polymers from the Dose Dependence of the Weight- and z-Average Molecular Weights

A procedure has been developed for the determination of scission and cross-linking fields, G(S) and G(X), in irradiated polymers by combination of the ordinate intercepts of plots of ([Mw(0)/ MW(D)] - 1)/D and ([Mz(0)/A/2(D)] - 1)/D versus dose (D). The required weight- and z-average molecular weight data for a given sample can be obtained by using the Rayleigh and schlieren optical systems, respectively, to record the solute distribution in a single sedimentation equilibrium experiment. The procedure has been tested by application to simulated data for a range of initial molecular weight distributions and values of G(S)/G(X) and applied to previous sedimentation equilibrium results (Nichol, J. M.; Donnell, J. H.; Rahman, NLP.; Winzor, D. J. J. Polym. Sci., Polym. Chem. Ed. 1977,15, 2919) for a polystyrene sample with Afw(0)/Mn(0) = 1.03 and G(S)/G(X) = 1