Protection in radiolysis of n-hexadecane—2. Radiolysis of n-hexadecane in the presence of additives

Protection effect of aromatic (naphthalene, phenanthrene) and hydroaromatic (tetralin, octahydrophenanthrene) compounds in irradiated liquid alkane has been investigated as a model experiment for the radiolysis of polymers. Liquid n-hexadecane has been selected as the model linear amorphous polymer and the protection effect has been studied by analyzing the radiolysis products. In the presence of additives, degradation of n-hexadecane, reduction of radiolysis products, including H₂ evolution, and selective degradation of the additive have been observed. Energy transfer (excitation and charge) to the additive reduces the solvent excitation which is the precursor of the radiolysis products. The additive reacts with the solvent molecules according to its reactivity to form adduct compounds. Mass analysis shows that these adduct compounds have a smaller number of double bonds in their aromatic rings due to hydrogenation. Aromatic compounds are more reactive than hydroaromatic compounds towards n-hexadecane and their adducts consume more hydrogen than those of the hydroaromatic compounds, and therefore aromatic compounds reduce gas formation more effectively than hydroaromatic compounds. From the effect of aromatic compounds, it is concluded that hexadecene is produced neither by H₂ elimination from the lowest excited state of n-hexadecane nor by disproportionation of n-hexadecyl radicals, but is mainly produced directly from the decomposition of the excited cations of n-hexadecane.