Crosslinking of polysilanes by ion beam irradiation

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 Kr-86(14+), 200 MeV Xe-129(14+) and 120 MeV Ne-20(5+) ions. PMPSi was also irradiated with 65 MeV N-15(5+) and 95 MeV Ar-40(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 Co-60-gamma-rays (dE/dx = 0.02-0.03 ev/Angstrom) 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, dE/dx). 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 dE/dx, e.g. in the case of PMPSi G(X) increases from 0.024 to 0.42 by increasing dE/dr from 42 to 565 eV/Angstrom. (C) 1998 Elsevier Science B.V. All rights reserved.