DIELECTRIC AND MECHANICAL-BEHAVIOR OF POLYURETHANE NETWORKS FROM POLY(OXYPROPYLENE)DIOLS OR POLY(OXYPROPYLENE)TRIOLS AND DIISOCYANATE

Thermally stimulated depolarization currents and dielectric and dynami c mechanical behaviour of polyurethane networks prepared from poly(oxy propylene)diols or -triols and 4,4'-diphenylmethane diisocyanate were studied. While the frequency and temperature positions of mechanical a nd dielectric functions are predominantly determined by the concentrat ion of polar urethane groups in the network chain, the equilibrium mod ulus correlates with network chain length. The effect of the chain pol arity on the shape of loss permittivity vs. frequency curves is more p ronounced in the low frequency region than in the high frequency one a nd is practically the same for stoichiometric and off-stoichiometric n etworks measured earlier.