MODEL EXPERIMENT ON THE PROTECTION EFFECT IN POLYMERS - RADIOLYSIS OFLIQUID SQUALANE IN THE PRESENCE AND ABSENCE OF ADDITIVES

A model experiment to clarify the elementary processes in aliphatic po lymers irradiated under vacuum has been carried out. Liquid squalane h as been selected as the model of branched polyethylene, ethylene-propy lene copolymers or polypropylene. The main gaseous product is H-2. The presence of methyl side groups increases the probability of main chai n scission, and side chain scission produces methane as the main hydro carbon gas product. The prominence of main chain scission and the chem ical structure of the parent molecule are believed to be the reasons f or formation of less oligomeric products. On the other hand, they prom ote the combination of the scission fragment with the parent radicals to produce intermediate compounds. In the presence of aromatic additiv es which have a lower ionization potential and lower excited state ene rgy level than the squalane itself, energy and charge transfer to the added molecules take place and both solvent decomposition and product formation including H-2 evolution are significantly reduced. Due to th ese transfer processes, the added molecules react with squalane molecu les to produce adduct compounds which are clearly observed from the ma ss analysis. A further inspection of the mass spectra shows that scave nging of hydrogen atoms occurs through hydrogenation of the benzene ri ngs in the adducts. Since the adduct compounds of aromatic additives c onsume more hydrogen atoms than those of hydroaromatic additives, arom atic compounds reduce H-2 evolution more effectively than do hydroarom atic compounds. Since main chain scission is not affected by any of th e additives, it is suggested that this scission process directly origi nates from the decomposition of the excited cations of squalane. The G -values in the radiolysis of liquid alkanes and base polymers are also compared.