Three kinds of poly(ether sulfone) copolymer samples, R50, 1350, and A50, showing marked differences in tensile behavior because of different sequence distributions were investigated by radial distribution function (RDF) methods. The RDF patterns were not virtually identical and showed that the short-range order (0-14 A) in the samples had been essentially affected by the sequence distribution. Most of the intramolecular distances in the copolymer were successfully resolved in the RDF pattern. However, there were only suggestions of broad peaks at r = 5.5 angstrom and r = 11 angstrom, attributable to intermolecular ordering, which indicated that little intermolecular ordering had occurred in either sample. The appearance two peaks at about 5 A periodic suggested the existence of more or less parallel chain segments in the copolymers Therefore, substantial structural differences between three copolymers were shown. The structural information revealed by these RDF results was in agreement with the tensile property changes caused by the sequence distribution . (c) 2006 Wiley Periodicals, Inc.