Unstabilized polypropylene (PP) films having selective 13 C isotopic labeling were subjected to thermal aging at 50, 80, and 109°C and to γ-irradiation at 24 and 80°C. The oxidized films were examined using solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy. Dramatic differences were found in the type and distribution of oxidation products originating from the three carbon atom sites within the PP macromolecule (tertiary carbon, secondary carbon, and methyl side group). Most of the oxidation products that formed on the polymer chain originated through chemical reactions at the PP tertiary carbons. Under all of the aging conditions examined, tertiary peroxides (from the PP tertiary site) were the most abundant functional group produced. Also originating from the PP tertiary carbon were significant amounts of tertiary alcohols, together with several more minor products that included "chain-end" methyl ketones. No significant amount of peroxides or alcohols associated with the PP secondary carbon sites was detected. A substantial yield of carboxylate groups was identified (acids, esters, etc.). The majority of these originated from the PP secondary carbon site, from which other minor products also formed, including in-chain ketones. We found no measurable yield of oxidation products originating from reaction at the PP methyl group. Remarkably similar distributions of the major oxidation products were obtained for thermal aging at different temperatures, whereas the product distributions obtained for irradiation at the different temperatures exhibited significant differences. Time-dependent concentration plots have been obtained, which show the amounts of the various oxidation products originating at the different PP sites, as a function of the extent of material oxidation.

In cold-drawn, necked high-density polyethylene, solid-state nuclear magnetic resonance (NMR) has identified a major fraction of chain segments intermediate to the ordered crystalline and the almost isotropic amorphous phases. This partially mobile and disordered all-trans fraction in the strain-hardened sample contains 38 ± 6% of all chain segments in the bulk. Thus, it represents the second largest component in the system, ahead of the disordered gauche-containing or amorphous (17 ± 4%) and the monoclinic crystalline (4 ± 2%) phases. A series of one- and two-dimensional NMR experiments, several of which make use of an “inverse 13C T 1 relaxation time filter” for selective observation of the intermediate-component signals, show the intermediate component (or components) to consist of all-trans chains with disordered packing. While the crystalline component has a standard deviation of the chain axis from the draw direction of 1°, the intermediate components exhibit an ∼8° spread of chain-axis orientations from the draw axis. The chains in the intermediate components undergo fast rotational motions around their axes, with motional amplitudes of ca. 20°.