The transesterification behavior of a poly (butylene terephthalate) (PBT)/polycarbonate (PC) blend with the addition of di-n-dodecyl phosphate was studied with differential scanning calorimetry (DSC) and infrared spectroscopy. The effects of triphenyl phosphate (TPP) and di-n-dodecyl phosphate on the suppression of transesterification were compared. The differences in the crystallization and melting temperatures during the two heating and cooling cycles in the DSC measurements were lower than those of the virgin PBT/PC blend, and di-n-clodecyl phosphate inhibited the formation of a random copolyester but did not suppress the formation of a block copolyester. The crystallization temperature of the PBT/PC blend in the presence of di-n-dodecyl phosphate was higher than that of the blend in the presence of TPP. Din-dodecyl phosphate was thus more effective than TPP in the inhibition of transesterification between PBT and PC. (c) 2008 Wiley Periodicals, Inc.