The structures of atomic-scale free-volume holes in stretched [poly(aryl-ether-ether-ketone)] PEEK and [poly(methyl methacrylate)] PMMA polymers were determined as a function of orientation by measuring the angular correlation of annihilation radiation from parapositronium trapped in the holes. The measured average hole diameters were found to range from 0.80±{}0.03 to 0.31±{}0.02 nm and from 0.70±{}0.03 to 0.42±{}0.02 nm, depending on orientation, in stretched PEEK and PMMA, respectively. Thus, the free-volume holes were ellipsoids with anisotropies of 2.6±{}0.2 and 1.7±{}0.2 for PEEK and PMMA, respectively.
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Jean et al. (1990) studied this question.
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