BROAD-BAND DIELECTRIC-RELAXATION SPECTROSCOPY IN INTERPENETRATING POLYMER NETWORKS OF POLYURETHANE-COPOLYMER OF BUTYL METHACRYLATE AND DIMETHACRYLATE TRIETHYLENE GLYCOL

The electrical and dielectric properties of interpenetrating polymer n etworks (IPNs) based on crosslinked polyurethane (PUR) and a copolymer of butyl methacrylate and dimethacrylate triethylene glycol were stud ied by means of broadband AC dielectric relaxation spectroscopy to obt ain information on the morphology and phase separation in these IPNs, Three relaxation processes were observed: a secondary beta relaxation due to the copolymer, the alpha relaxation due to the glass-rubber tra nsition of the PUR phase and a conductivity current relaxation due to charge carriers trapped at the interfaces in the microheterogeneous sa mples. The alpha relaxation due to the glass-rubber transition of the copolymer is masked by conductivity effects and is revealed after a fi tting treatment. The dipolar alpha and beta mechanisms and the AC cond uctivity mechanism were studied in detail at several IPN compositions, by analysing the dielectric susceptibility data within the complex pe rmittivity formalism, the modulus formalism and power law forms. For t he copolymer network, the dielectric loss epsilon ''(omega) shows a st rong secondary beta relaxation which becomes faster in the IPNs. The P UR network displays a relatively broad alpha-relaxation process which becomes slower in the IPNs, The energy and shape parameters of the res ponse were determined for both mechanisms at several temperatures, Fro m AC conductivity measurements we extracted information about the morp hology and local structure of the IPNs, II is concluded that the IPNs studied are two-phase systems, but phase separation is incomplete in t hese materials. (C) 1998 Elsevier Science Ltd. All rights reserved.