Relaxation!transition behaviours for copolyesters made from poly(ethylene terephthalate) (PET) and p-acetoxybenzoic acid (POB) have been characterized by thermally stimulated current (TSC) measurement. The sequence distribution, in terms of the degree of blockiness, in dual chemidomains of POB/PET copolyester is simulated from a model developed by us to predict the probability between block sequence and random sequence under a given composition and measuring condition. It is found that the degree of blockiness, a measure of sequence distribution, under the same polarization temperature generally increases with increasing POB content in the POB/PET copolyester. For copolyesters of the same composition, the degree of blockiness shows a large decrease after solid-state polymerization when high molecular weight PET is used, whereas it shows only a small decrease or an increase after solid-state polymerization when PET of lower molecular weight is used. It is concluded that the change in the degree of blockiness caused by the solid-state polymerization of copolyesters is dependent on the molecular weight of sequences of the PET moiety in the structure.