Crosslinking of polysilanes by ion beam irradiation

Abstract Poly(methyl phenyl silane), PMPSi, poly(biphenyl methyl silane), PBMSi, poly(c-hexyl methyl silane), PcHexMSi, and poly(methyl n-hexyl silane), PMnHexSi, were irradiated in the absence of air with 300 MeV 86 Kr 14+ , 200 MeV 129 Xe 14+ and 120 MeV 20 Ne 5+ ions. PMPSi was also irradiated with 65 MeV 15 N 3+ and 95 MeV 40 Ar 5+ ions. In all cases, the ion beam irradiation induced insolubilization of the polysilanes indicating that intermolecular crosslinking dominates over main-chain scission. By contrast, irradiation with 60 Co-γ-rays (d E /d x =0.02–0.03 eV/A) led to a decrease in the average molar mass indicating that main-chain scission is the dominating effect when the polysilanes are subjected to radiation of low linear energy transfer (LET, d E /d x ). In the case of ion beam irradiation the dose to gelation, D gel , was determined by solubility tests. D gel is inversely proportional to G ( X ), the number of crosslinks per 100 eV absorbed by the polymer. On this basis G ( X ) was estimated and it turned out that G ( X ) increases with increasing d E /d x , e.g. in the case of PMPSi G ( X ) increases from 0.024 to 0.42 by increasing d E /d x from 42 to 565 eV/A.