FREE-VOLUME AND DIPOLE MOBILITY IN AN EPOXIDE OLIGOMER BEFORE CROSS-LINKING

The free volume of a bisphenol-A-type epoxide oligomer (DGEBA) was stu died using Williams-Landel-Ferry parameters and thermal expansion coef ficients above and below the glass transition temperature (T-g). The v alues of the free-volume fraction at the T-g are around 0.02 for the D GEBA oligomers having weight-average molecular weights ((M) over bar(w )'s) from 1396 to 2640. The dipole mobility, which was obtained from t he analysis of the temperature dependence of the dielectric relaxation time, was compared with the segment mobility in terms of the critical volume for the transport of each moving unit. The critical volume for the segment transport increases with increase of the M, of the oligom er. The critical volume for the dipole movement, on the other hand, is not different between the oligomers studied (1396 less than or equal to (M) over bar(w) less than or equal to 2640), which leads to that th e dipole mobility in the epoxide oligomer is smaller than is the segme nt mobility. The low mobility of the dipole is considered to result fr om the molecular interaction restricting the dipole movement, especial ly in a smaller (M) over bar(w) oligomer. (C) 1999 John Wiley & Sons, Inc.