TRANSESTERIFICATION IN HOMOGENEOUS POLY(EPSILON-CAPROLACTONE)-EPOXY BLENDS

Transesterification has been investigated in poly(epsilon-caprolactone ) (PCL)-epoxy blends. In the hot melt process, the hydroxyl on diglyci dyl ether of bisphenol-il (DGEBA) monomers is too low to give a notice able transesterification reaction. In the postcure process, model reac tions reveal that the hydroxyls from a ring-opening reaction are able to react with the esters of PCL. In the meantime, the PCL molecular we ight decrease and its distribution becomes broader. Nuclear magnetic r esonance spectra reveal that fraction of the tertiary hydroxyls conver ts to secondary hydroxyls. In the cured EBA-3,3'-dimethylmethylene-di( cyclohexylamine)-PCL blend, a homogeneous morphology is achieved. PCL segments are grafted onto the epoxy network after postcuring and resul t in the lower T-g observed in the differential scanning calorimetry t hermogram. A higher transesterification extent also results in broader transition peaks by dynamic mechanical analysis. (C) 1999 John Wiley & Sons, Inc.