Analysis of the gases evolved from irradiated polyethylene

Saturated hydrocarbons evolved during electron irradiation of polyethylene are characteristic of short side chains in the polymer. A convenient analysis is effected by programmed temperature gas chromatography. In order to minimize the relative concentrations of extraneous hydrocarbons, i.e., those not arising from selective scission of complete side chains, it is necessary to irradiate at low temperatures and doses. Such analyses of a high pressure polyethylene (DYNK) indicates that the two methyls per 100 carbon atoms detected in infrared absorption are probably equal amounts of ethyl and butyl branches. These arise by intramolecular chain transfer during polymerization. At a dose of 10 Mrad about 1/4% of the alkyl groups are removed. Methane is the only hydrocarbon detected on irradiation of polypropylene, indicating little combination of methyl radicals to form ethane during irradiation.