Nitric acid oxidation of irradiated polyethylene

Samples of high‐density polyethylene were irradiated with x‐rays and oxidized with concentrated nitric acid to determine the location of unsaturated groups. Vinyl groups initially present in the polymer were rapidly oxidized to the extent of 85% and are assumed to be excluded from the crystals. Vinylene groups show a rapid oxidation followed by slow oxidation. The initial oxidation is about 35%, which is slightly greater than the 25% amorphous content of the polymer prior to irradiation. Diene groups are rapidly oxidized by nitric acid but are formed at about the same rate in crystalline and amorphous samples. This is interpreted to indicate that diene groups are formed throughout the polymer but form large defects in crystalline regions and are accessible to oxidation. Defects formed in crystalline regions during irradiation lower the melting point to a greater extent than predicted by the mole fraction of noncrystallizable units.