The phase behavior of Poly(ethylene terephthalate)/Poly(ethylene-2,6-naphthalate)/Poly(ethylene terephthalate-co-ethylene-2,6-naphthalate) (PET/PEN/ P(ET-co-EN)) ternary blends in molten state was evaluated from differential scanning calorimetry (DSC) and NMR results as well as optical microscopic observations. Copolymer of ethylene terephthalate and ethylene-2,6-naphthalate was prepared by a condensation polymerization, which was a random copolymer with an intrinsic viscosity (IV) of 0.3 dL/g. The phase diagram of the ternary blends revealed that the miscibility of ternary blends in molten state was dependent on the fraction of P(ET-co-EN) in the blends and holding time of the blends at high temperatures above 2808C. With increase in the holding time, the fraction of copolymer in the blends necessary to induce the immiscible to miscible transition decreased. For the blends with longer holding time at 2808C, the phase diagram in molten state was irreversible against the temperature, although a reversibility was found for the blends with short holding time of 1 min at 2808C. The irreversibility of phase behavior was not explained simply by the increase of copolymer content produced during heat treatment. Complex irreversible physical and chemical interactions between components and change of phase structure of the blend in the molten state might influence on the irreversibility.

The extent of transesterification in poly(ethylene terephthalate) (PET)/poly(ethylene-2,6-naphthalate) (PEN) blends with the addition of PET-PEN copolymers was examined by DSC and 1 H-NMR measurements to evaluate the factor affecting the reaction level at a given temperature and time. Both block (P(ET-block-EN)) and random (P(ET-ran-EN)) copolymers were used as the copolymers. At a given treatment temperature and time, the level was increased by the addition of P(ET-block-EN) into PET/PEN blends. On the other hand, a reverse change was observed when P(ET-ran-EN) was mixed with PET/PEN blends. During the treatment, an inhomogeneous phase of the blends changed into the homogeneous one; however, the change showed little effect on the reaction level. The effects of molecular weight on the reaction level were also examined.

ABSTRACT:The phase structure of poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalate) (PET/PEN) blends was studied in relation to the molecular weight. The samples were prepared by both solution blends, which showed two glass-transition temperatures (T g ), and melt blends (MQ), which showed a single T g , depending on the composition of the blends. The T g of the MQ series was independent of the molecular weight of the homopolymer, although the degree of transesterification in the blends was affected by the molecular weight. The MQ series showed two exotherms during the heating process of a differential scanning calorimetry scan. The peak temperature and the heat flow of the exotherms were affected by the molecular weight of the homopolymers. The strain-induced crystallization of the MQ series suggested the independent crystallization of PET and PEN. Based on the results, a microdomain structure of each homopolymer was suggested.