High temperature bulk reaction between poly(ethylene terephtalate) and lactones: H-1 NMR and SEC/MALDI-TOF MS study

摘要

Copolyesters containing aliphatic units in the main chain were obtained by reacting high molar mass poly(ethylene terephthalate) (PET) with e-caprolactone or delta-valerolactone at high temperature in the bulk. T-Butyrolactone did not react in these conditions. Thermal properties were studied by DSC and TGA, and structural characterizations were carried out by H-1 NMR spectroscopy and SEC/MALDI-TOF mass spectrometry off-line coupling. These I techniques demonstrate the insertion of lactone units in PET chains. Linear species with hydroxy, carboxy and vinyl ester end-groups were clearly identified in the mass spectra, together with cyclic copolymer species. Narrow-distribution copolyester SEC fractions were characterized by MALDI-TOF mass spectrometry and used to establish a SEC calibration curve against absolute molar masses. The results indicate that the conventional polystyrene SEC calibration strongly overestimates copolyester molar masses. The degree of randomness of these copolyesters, determined by H-1 NMR, shows that chain microstructure presents some block-copolymer character. The thermal properties of the copolyesters are also discussed.