Crystal structures have been determined by the X-ray diffraction analyses for a series of aromatic polyesters -[-O(CH2)(m)O-COC6H4CO-](n)- (mGT) with the long methylene sequence (m = 9-20) and their model compounds. The X-ray diffraction spots of these polyesters were observed more or less to shift upward and downward slightly from the averaged horizontal layer lines, indicating the tilting phenomenon of the molecular chains from the draw direction, the analysis of which was helpful for the definite determination of the unit cell parameters. For example, the c axis of 10 CT was found to be tilted by about 1 from the drawn axis in the 710 tilt plane. The unit cell parameters obtained by the quantitative analysis of the tilting phenomenon were a = 4.77 0.01 A b = 5.66 0.01 A, c (fa.) = 20.7 0.1 A a= 108.2 0.1, fl 122.7 0.2, and 7 = 97.1 0.1. In the case of 20 GT, the tilting phenomenon was not observed in the X-ray fiber diagram. The triclinic unit cell parameters were determined for 20 GT: a = 4.59 0.02 A, b = 5.75 0.02 A, c (fa.) = 333 0.1 A a = 113.2 0.2, 13 = 116.6 0.2, and 7 = 98.1 0.2. The space group was PT for both of 10 GT and 20 GT. One chain is included in the unit cell. The chain conformation is of the all-trans-zigzag type. The reliability factor or the measure of the agreement between the observed and calculated X-ray diffraction intensity was 18.8% for 10 GT (90 reflections in total) and 18.5% for 20 GT (67 reflections). The crystal structures of 12 GT and 16 CT were found to be essentially the same as those of 10 GT and 20 GT. As for the odd-numbered mGT or 9 GT, 11 CT and 15 GT, the most plausible structure models were built up, which gave the good correspondence to the observed diffraction patterns semi-quantitatively. As the total number of methylene monomeric units was increased, the chain conformation was found to change from the trans-gauche combined form (3 GT and 5 GT) to the all-trans form (15 GT). The single crystal structure analysis of the low-molecular-weight model compounds confirmed the reasonableness of the crystal structures of the corresponding polymers. 2014 Elsevier Ltd. All rights reserved.