Three model reactions are designed to investigate the transesterification between carbonate of PC and hydroxyl group formed from the ring opening reactions of oxirane with amine. Results show that the observed PC-epoxy blend cured by aromatic diamine-metaphenylene diamine (MPDA) and the i.r. absorption band of carbonate group shifts to low frequency during the curing procedure. The product of transesterification reaction accelerates the reaction between epoxy and amine. The transesterification reaction scissors the long chain of PC to short segments, decreasing the T(g)s of the blend system.