Crosslinking of polysilanes by ion beam irradiation

Poly(methyl phenyl silane), PMPSi, poly(biphenyl methyl silane), PBMSi, pol y(c-hexyl methyl silane), PcHexMSi, and poly(methyl n-hexyl silane), PMnHex Si, 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 M eV N-15(5+) and 95 MeV Ar-40(5+) ions. In all cases, the ion beam irradiati on induced insolubilization of the polysilanes indicating that intermolecul ar crosslinking dominates over main-chain scission. By contrast, irradiatio n with Co-60-gamma-rays (dE/dx = 0.02-0.03 ev/Angstrom) led to a decrease i n the average molar mass indicating that main-chain scission is the dominat ing effect when the polysilanes are subjected to radiation of low linear en ergy 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 pr oportional to G(X), the number of crosslinks per 100 eV absorbed by the pol ymer. On this basis G(X) was estimated and it turned out that G(X) increase s with increasing dE/dx, e.g. in the case of PMPSi G(X) increases from 0.02 4 to 0.42 by increasing dE/dr from 42 to 565 eV/Angstrom. (C) 1998 Elsevier Science B.V. All rights reserved.