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.

• Received 18 June 1990

DOI:https://doi.org/10.1103/PhysRevB.42.9705