Broadband dielectric relaxation spectroscopy in interpenetrating polymer networks of polyurethane-copolymer of butyl methacrylate and dimethacrylate triethylene glycol

Abstract

Abstract The electrical and dielectric properties of interpenetrating polymer networks (IPNs) based on crosslinked polyurethane (PUR) and a copolymer of butyl methacrylate and dimethacrylate triethylene glycol were studied by means of broadband AC dielectric relaxation spectroscopy to obtain information on the morphology and phase separation in these IPNs. Three relaxation processes were observed: a secondary β relaxation due to the copolymer, the α relaxation due to the glass–rubber transition of the PUR phase and a conductivity current relaxation due to charge carriers trapped at the interfaces in the microheterogeneous samples. The α relaxation due to the glass–rubber transition of the copolymer is masked by conductivity effects and is revealed after a fitting treatment. The dipolar α and β mechanisms and the AC conductivity mechanism were studied in detail at several IPN compositions, by analysing the dielectric susceptibility data within the complex permittivity formalism, the modulus formalism and power law forms. For the copolymer network, the dielectric loss e ″( ω ) shows a strong secondary β relaxation which becomes faster in the IPNs. The PUR network displays a relatively broad α -relaxation process which becomes slower in the IPNs. The energy and shape parameters of the response were determined for both mechanisms at several temperatures. From AC conductivity measurements we extracted information about the morphology and local structure of the IPNs. It is concluded that the IPNs studied are two-phase systems, but phase separation is incomplete in these materials.