Poly(2,6-Dimethyl-1,4-Phenylene Oxide) as a Polymer-Polymer Nanocomposite: Mechanical and Gas Transport Characteristics

This work analyses mechanical and gas transport characteristics of films prepared from two samples of poly(2,6-dimethyl-1,4-phenylene oxide) with molecular masses of 355 (PPO-1) and 610 (PPO-2) kDa. It has been shown using X-ray powder diffraction method that virgin semi-crystalline PPO-1 samples contain only beta-modification of the crystalline phase, and PPO-2 films also include alpha-modification of the crystalline phase. Phase composition of the samples under investigation significantly affects their mechanical and gas transport properties when uniform biaxial deformation is performed. Judging by the measured mechanical and gas transport parameters, semi-crystalline PPO films may be considered a polymer-polymer nanocomposite with a dispersion low-density highly permeable nanocrystalline phase distributed in the amorphous matrix of the same polymer. Non-oriented nanocrystalline phase of PPO forms highly permeable percolation cluster at high concentration. Uniform biaxial deformation of the films does not lead to changes in the beta-modification of nanocrystalline PPO phase, while the alpha-modification of the nanocrystalline PPO phase aligns along the deformation direction. As a result, both mechanical and gas transport properties of the composite drastically differ between oriented and non-oriented samples. Percentage elongation for non-oriented PPO-1 and PPO-2 films was not exceeding 12%, while for oriented PPO-2 films higher and lower yield points are observed in stress-strain curves and percentage elongation increases to 217%. Gas diffusion and permeability coefficients reduction for the oriented samples of PPO-2 demonstrates the presence and aligning of alpha-modification of PPO crystalline phase.