PET/PHB‐LC polyesters with improved mechanical properties — terminal group coupling with diisocyanate, I

In order to increase the molecular weights of poly(ethylene terephthalate‐co‐oxyben‐zoate)s (PET/PHB) these polymers were modified with methylene‐diphenyldiisocyanate (MDI) in the melt to couple the carboxy terminal groups, forming a copolyester amide. Starting from M̄n 12 500, various M̄n values, partly up to 60 400, were obtained in dependence on the MDI quantity. The copolyester amides were characterized by IR spectroscopy, DSC, M̄n and rheological measurements. The MDI modification of PET/PHB causes also an increase in melt viscosity and a decrease in crystallinity in the solid state. Injection molded samples showed a considerable increase in tensile strength, elastic modulus and above all impact strength.