Free Volume in Epoxide Oligomers

Abstract

Free volume studies are reviewed for the oligomers of the diglycidyl ether of bisphenol-A (DGEBA) before cross-linking. The Williams-Landel-Ferry (WLF) method was used to analyse the macroscopic free volume in the DGEBA oligomers in comparison with that in the crosslinked DGEBA network. The crosslinked system has relatively large fractional free volume at the Tg. The DGEBA oligomers have bulky bisphenol-A structure. The cross-link sites in the network structure does not always provide a suitable environment for close packing of rigid molecules. The WLF type equations are applicable to the temperature dependencies of the melt viscosity, the dielectric relaxation time, and the ionic conductivity for the uncured DGEBA oligomer. These three viscoelastic properties are discussed in terms of the movements of three moving units: the chain segment, the dipole, and the ionic charge carrier. The mobility difference between the three moving units is clarified from the standpoint of the free volume concept.