The changes of transesterification level in PET/PEN blends with the addition of PET–PEN copolymer

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 ¹H‐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. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009