The microstructure of 50% PET/PEN random copolymer crystallised by uniaxial drawing and subsequent annealing is investigated by two-dimensional wide angle X-ray diffraction and high resolution scanning electron microscopy. Chemical etching was used to reveal the structure after drawing and subsequent annealing. The structure observed was found to be in the order of 100 nm. The results showed fibrillar microstructure parallel to the draw direction that could be associated with the presence of the smectic-A liquid crystalline transient mesophase as a result of the drawing. There was evidence of banding perpendicular to the draw direction when crystallisation started to take place. This banded structure was explained in terms of buckling of the thin polymer film perpendicular to the direction of the draw in an analogy similar to that of liquid crystalline polymers. The wide range of microstructure observed microscopically and reported here are, however, associated with crystallisation. (c) 2007 Elsevier Ltd. All rights reserved.