Dielectric relaxation of poly(ethylenglycol)-b-poly(propylenglycol)-b-poly(ethylenglycol) copolymers above the glass transition temperature

The complex dielectric permittivity has been measured for three poly(ethyle nglycol)-b-poly (propylenglycol)-b-poly(ethlylenglycol) copolymers with dif ferent content of poly(ethylenglycol) (15%, 33% and 80%), and increasing de gree of crystallinity (0%, 10% and 20%, respectively). Only the noncrystall ine sample shows the normal mode relaxation together with the segmental (al pha -relaxation) and the Johari-Goldstein (beta -relaxation) modes. The cry stalline samples show also polarization contributions due to the existence of interfaces between the crystallites and the amorphous phase. The relaxat ion times of the (alpha and normal modes can be described by a VFT equation with the same value of T-0. There is a slowing-down of the segmental mode due to the presence of crystallites. The temperature dependence of the alph a and beta relaxations in the copolymers is very similar to that found in p ure PPG, while there are significant differences in the case of the normal mode of the non-crystalline sample. The size of the cooperatively rearrangi ng regions CRR, and the width of the glass transition region increase sligh tly with the degree of crystallinity. The temperature dependence of the siz e of CRRs is compatible with the prediction of fluctuation theory. No syste matic effect of the degree of crystallinity on the beta -relaxation has bee n found. Near T-g the beta -relaxation time is close to the primitive time of the coupling model.