Extensive cis-trans Isomerization of Carboxyl Groups in Thermal Polyesterification of 5-Norbornene-2, 3-dicarboxylic Anhydride with Glyc o l s t -The Study on Polysters by NMR Spectrometry. II.-

Abstract

The structure of polyesters which were prepared from 5-norbornene-2, 3-dicarboxylic anhydride as an acidic component and ethylene glycol or propylene glycol as an alcoholic cornponent has been analyzed by means of proton NMR spectroscopy. Extensive geometrical isomerization of carboxyl groups from cis-form to trans-form was observed in the early stage of polyesterification reaction. Mechanistic investigation suggested that the retro-DielsAlder reaction is responsible for the formation of trans-isomer.