AbstractThe effects of extreme uniaxial orientation on gas permeation through dibutyl maleate–thylene copolymer films have been examined. Gases employed were helium, argon, and methane. Permeability constants were measured as functions of temperature between 25 and 55°C., in unstretched film and in films stretched to elongations of 490, 512, 540, and 608 (breaking point). Uniaxial cold drawing of dibutyl maleate–ethylene copolymer films into the stable necking region (elongation ca. 490) causes only a small (30) decrease in permeability and virtually no change in apparent activation energy of permeation; when the necked films are further stretched to elongations approaching the breaking point (ca. 600), a significant decrease in permeability and increase in activation energy is observed. It is deduced that the major changes in crystalline texture and arrangement which this polymer undergoes in the necking process have only a minor effect upon total level of crystallinity, amorphous‐phase properties, and diffusional impedance offered by the crystallites, suggesting that changes in crystallite orientation, perfection, and shape throughout the drawing process are compensatory. When necked polymer is further stretched, however, severe restraints are imposed upon the mobility of oriented chain segments in the amorphous regions, which are primarily responsible for the observed large changes in permeabilities and permeation activation en
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