Random segmented copoly(ether ester)s were synthesized by reacting terephthaloyl chloride sequentially with poly(oxytetramethylene) glycol ((M) over bar(n) = 250, 650, 1000, 2000 g mol(-1)) and hydroquinone via melt condensation. A series of copolymers were obtained by maintaining a constant weight ratio of hard to soft segments, which results in simultaneous variation of hard/soft-segment lengths. The properties of these copolymers with oxy-1,4-phenyleneoxycarbonyl-1,4-phenylenecarbonyl hard segments and polyoxytetramethylene soft segments were studied for solubility behaviour, X-ray diffraction, infra-red spectroscopy, differential scanning calorimetry and polarizing microscopy. Thermal properties were found to vary with the hard-segment length. All copoly(ether ester)s are elastomeric at room temperature (25 degrees C). Polarizing microscopic observations are indicative of highly ordered smectic mesophases, which owe their origin to the hard segments.