The synthesis and characterisation of the thermotropic polyester poly[oxy-(1,4-dimethyltetramethylene)oxycarbonyl-3-chloro-1,4-phenyleneoxyterephthaloyloxy-2-chloro-1,4-phenylenecarbonyl] is described, and its thermal behaviour analysed. The effect of asymmetrical substitution in the tetramethylene spacer is analysed and the polymer compared with its non-substituted homologue. Substitution of methylene units at the 1,4 positions in the spacer results in a considerable lowering of the both the transition temperatures and the associated molar enthalpies, and inhibits the formation of three-dimensional order.