Fully aromatic copolyesters with regular chain structure containing kinked monomer units were investigated by powder diffraction experiments combined with structure modelling. The proposed series of copolyester structures including isophthalic acid was continued with (TPA-HQ-IPA-HQ), (containing 104 atoms as repeating unit). The monoclinic unit cell has a = 0.781 nm, b = 0.557 nm, c = 5.03 nm and beta = 89.2 degrees as atom coordinates. The symmetry of the unit cell was determined by means of a force field constrained Rietveld refinement algorithm including nonbonding interactions (Lennard-Jones potentials) and chain continuation enforcement (penalty functions) in the force field. A reliability factor R-Rietveld of 9.5% was calculated. (C) 2000 Elsevier Science Ltd. All rights reserved.