Oxygen adsorption on poly(2,6-dimethyl)phenyleneoxide: a solid state 1H NMR study

Solid aromatic polymers are capable of adsorbing O₂ molecules on aromatic rings selectively. The amount of adsorbed oxygen is affected by the chemical nature of the polymer, by the crystalline amorphous ratio, by the kind of crystal structure (polymorphism), and by molecular motions. In particular poly(1,4-oxy 2,6-dimethyl)phenylene is capable of adsorbing large amounts of O₂ as demonstrated by its selectivity in O₂/N₂ permeability. A ¹H-NMR relaxation study was performed on solid PPO as a function of temperature, and at different [PPO]/[O₂] molar ratios. At low temperature an almost quantitative PPO-oxygen complexation is demonstrated. Moreover a careful study of NMR relaxations T₁, T_1p, of i.r. spectra, and a comparison with literature data, reveals the presence of two dynamic transitions at temperatures well below the T₈. One of these transitions is frequency dependent and probably related to a delocalized motion along the backbone; the other one, frequency independent, seems to be related to a ring flip.