Molecular weight distribution of proton irradiated polystyrene studied by diffusion experiments

Abstract

MeV ion irradiation of polymers induces break-up or crosslinking of polymer chains. This leads to an ion-fluence dependent molecular weight (MW) distribution ranging from short scission fragments via larger chain clusters to the interconnected, immobile network fraction. We used diffusion experiments to obtain information about the MW distribution of the mobile chains in dependence of the ion fluence. Double layers of deuterated (dPS) and protonated (hPS) polystyrene on Si wafer substrates were irradiated by 1MeV protons and annealed at 140°C for various periods of time. The dPS diffusion depth profiles in the irradiation induced hPS network were measured by 3He nuclear reaction analysis. For calibration the strongly MW dependent diffusion coefficients of dPS chains in hPS networks were determined separately by analogous techniques. The depth profiles were fitted with MW dependent diffusion profiles convoluted with a parametrized MW distribution, and the resulting MW distribution was compared to theory.