Most probable distance between adjacent molecular chains was evaluated as the first trial for oriented amorphous polymers, using the two-dimensional radial distribution function formulated by a series expansion of Bessel and Legendre functions of coherent X-ray intensity curves. Poly(phthalazinone ether ketone) (PPEK) was selected as the test specimen, since PPEK dissolved in some solvents was one of typical amorphous polymers with high impact strength and high-temperature resistance and PPEK could produce fine fibers by dry spinning in spite of amorphous polymer. Non-crystallization of PPEK chains were analyzed in comparison with chain structure of undrawn amorphous poly(ethylene terephthalate) triggering oriented crystallization. Additionally, the strain between adjacent PPEK chains under external stress along the fiber axis was measured by a homemade instrument in relation to the chain orientation degree. These results indicated that the amorphous chains were connected with strong intermolecular force between adjacent PPEK chains, and the force could achieve fiber spinning. (C) 2016 Published by Elsevier Ltd.