Transesterification of poly(ethylene terephthalate) (PET) with poly(ε-caprolactone) (PCL) was investigated bymeans of NMR spectroscopy

extraction experiments

differential scanning calorimetry (DSC) and phase contrast microscopy(PCM). The 1H-NMR results show that transesterification takes place in the melt blends and leads to the formation of thePET-PCL copolyester with a chemical structure similar to ethylene terephthalate-ε-caprolactonc copolycster (TCL)synthesized directly from monomers.However

even in the blend that has been transesterified for 8 h

the random PET-PCL copolyester

PET-PCL copolyester with long PET or long PCL segments and the unreacted PET and PCL homopolymers may coexist.Due to the low mobility of PET and PCL chains and the high viscosity of the two macromolecules

the transesterification proceeds with difficulty.Furthermore

PET is incompatible with PCL

the transesterirication can only occur at the interface or in the interfacial region between two phases

and finally the reaction can only reach a local equilibrium.These results indicate that in fact the transesterification in the melt blend between two incompatible homopolymers could not lead to the formation of completely random or typical block copolyesters.