Radiation effects of paraffins as polymer model compounds—I. Evolved gas analysis

Abstract

Radiation yields of gases from n-paraffins of n-C 20H 42 to n-C 24H 50 and squalane (C 30H 62), as polymer model compounds, in the liquid and solid phases were analyzed by gas chromatography. G(H 2) in the liquid phase was 3.2–3.3 for all samples and found to be almost independent of the chemical structure and molecular weight; G(H 2) in the crystalline state of n-paraffins was 2.2–2.5 at -77 to 25°C. G(CH 4) was about 1% of G(H 2) for n-paraffins and increased with the methyl content of the branched chain for squalane. G(C 2H 6) in the liquid phase was about 0.05 for n-paraffins, but G(C 2H 6) in the crystalline state was found to depend on the crystal structure; that is, nearly zero for triclinic of an even number of carbons and about 0.02 for orthorhombic of an odd number. C 3H 8 and C 2H 4(C 3H 6 in squalane) were observed only in the liquid phase of n-paraffins and in glass and the liquid phase of squalane; G(C 3H 8) = 0.03–0.05 and G(C 2H 4 or C 3H 6) = 0.01–0.03. But the C 4-compounds were not detected in any phase of any of the samples. Chain scission by radiation is supposed to proceed mainly at chain end carbons until the third carbon in the liquid phase of n-paraffins, only at the chain end carbon of the crystalline surface in triclinic crystals and at chain end carbons until the second carbon in orthorhombic crystals. These chain scission phenomena in the liquid phase and crystalline state of n-paraffins and in the liquid phase of squalane would be analogous to those in the amorphous and crystalline states of polyethylene, and in amorphous ethylene-propylene copolymer, respectively.