Synthesis of bisoxazolines and their application as chain extender for poly(ethylene terephthalate)

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Abstract
A synthetic method was found to prepare 1,2‐bis‐(2‐oxazolinyl‐2)ethane (BOXE) from succinonitrile and ethanolamine. Succinonitrile is a vicinal dinitrile, which forms with ethanolamine succinimidine. This imidine can be converted in good yield into the corresponding BOXE by heating it while stripping off the excess of ethanolamine.Bisoxazolines react with the carboxylic endgroups of PET, giving a strong increase in viscosity. The efficiency of this chain extension reaction depends on the structure of the bisoxazoline. BOXE gives a sharp rise in the viscosity of PET after 2.5 min at 270 °C. After prolonged heating the viscosity decreases again, even under the level of the blank. A mechanism is given which describes this unusual behaviour. It is proposed that chain scission takes places in the newly formed esteramide bridge.