A two-stage copolycondensation of a mixture of equal parts of isophthalic acid and terephthalic acid was conducted using a tosyl chloride/dimethylformamide/pyridine condensing agent. In the initial stage x,y-dihydroxytoluenes (x,y-DHTs) or 2,4-dihydroxyethylbenzene (2,4-DHEB) was used and in the next stage isomeric DHTs or the DHEB was used. The results were examined in terms of how the reaction of the resulting oligomers with the next monomers proceeded, which was evaluated from distributions of the next monomers in the resultant copolymers as determined by H-1 NMR. A structurally selective reaction was observed. The preformed oligomers from symmetrically substituted 3,5-DHT reacted randomly with similarly substituted 2,6-DHT or asymmetric 2,4-DHEB, but those from 2,4-DHEB reacted selectively with both of 3,5- and 2,6-DHT. In the reactions of the oligomers from 2,6-DHT, they reacted randomly with 2,6-DHT but selectively with 2,4-DHEB. Such selective reactions were also observed in the reaction of p-isomeric 2,5-DHT with the oligomers prepared from 3,5- or 2,6-DHT. When the monomers were copolymerized simultaneously instead of stepwise, they distributed randomly in the resultant copolymers. (C) 2004 Wiley Periodicals, Inc.