THERMODYNAMIC STATE, TEMPERATURE TRANSITIONS, AND BROAD-BAND DIELECTRIC-RELAXATION BEHAVIOR IN GRADIENT INTERPENETRATING POLYMER NETWORKS

Traditional and gradient interpenetrating polymer networks (IPNs) of v arious composition have been prepared on the basis of crosslinked sili ceous polyurethane and a copolymer of butylmethacrylate and dimethacry late triethylene glycol. For various layers of gradient IPNs cut from the surface to the center of the sample detailed investigations by met hods of volume dilatometry, vapor sorption and broadband ac dielectric relaxation spectroscopy were carried out. From data of benzene vapor sorption by various layers of gradient IPN the free energy of mixing o f the IPN components has been calculated. For all the layers the free energies of mixing are positive and depend on the distance from the sa mple surface. Each layer consists of two phases with their own transit ion temperatures. From these data the composition of each phase for va rious layers has been calculated. The dipolar Lu mechanism of the poly urethane-rich phase and the ac conductivity mechanism were studied in detail by analyzing the dielectric susceptibility data within the comp lex permittivity and the modulus formalism. (C) 1998 John Wiley & Sons , Inc.