The transesterification of poly(bisphenol A carbonate) (PC) with ethylene terephthalate (ET)-caprolactone (CL) copolyester (TCL) was investigated with high-field H-1 NMR spectroscopy. Under an uncatalyzed condition, ET and CL segments in TCL reacted more easily with PC than the corresponding homopolymers poly(ethylene terephthalate) and poly(epsilon -caprolactone). In a comparison of the transferring rates, aromatic ET segments had higher reaction activity than aliphatic CL segments. Furthermore, the reaction activity appeared to be strongly dependent on the TCL compositions. High and low ET-segment contents were unfavorable to the exchange reaction for both ET and CL segments. These characteristics are discussed on the basis of the TCL structures. (C) 2000 John Wiley & Sons, Inc.