Abstract: Polyester-polyether multiblock copolymers with relatively high content of hard segment and molecular weight of soft segment exhibit low compositional homogeneity and a large amount of CHCl₃ insoluble fraction with high melting point can be separated out.The addition of 5% mol of dimethyl isophthalate(DMI)as a comonomer during ester exchange reaction much improves the apparent compositional homogeneity of the multiblock copolymers. The polyethylene terephthalate-polyethylene glycol ether multiblock copolymers(PET-PEG) with hard segment of 40wt% and PEG molecular weight of 4000 were synthesized with excellent mechanical properties and no CHCl₃ insoluble fraction.An alternative synthetic route has also been explored,according to which the PET is first acidolysed by isophthalic acid(IPA)and then copolycondensized with OH-terminated PEG to prepare PET-PEG with isophthalate units in hard segments.The compositional homogeniety of PET-PEG obtained greatly increases as the molecular weight of PEG decreases.

Key words: Modification via copolymerization, Polyester-polyether, Multiblock copolymer, Segmented copolymer