Immiscible blends of poly(ethylene terephthalate) (PET)/polyethylene (PE) and polycarbonate (PC)/PE were examined to study the influence of the high interfacial contact (pseudo-adhesion) on the mechanical properties and the morphology developed during elongation. The high inter-facial contact resulted from the contraction difference of the two polymers during cooling from the processing temperature to room temperature. As a result of the pseudo-adhesion, the tensile strength and modulus of the PET/PE and PC/PE blends increased steadily with the increase of PET and PC concentration. In PC/PE blends, numerous PC microfibers were formed in-situ, while in PET/PE blends, slippage took place between the PET particles and the matrix. Moreover, the macroscopic morphology development of both blends upon elongation was quite different. For PET/PE blend, necking was initiated at one point close to the non-gate end of the specimen, and then propagated uniformly from this point. For the PC/PE blend, necking-initating sites and propagation were irregular, and consequently the whole tested zone was deformed. The recoil of partially elongated specimens indicated that the recoverability of the PC/PE blend is higher than that of the PET/PE blend. Polym. (C) 2004 Society of Plastics Engineers.