Thermally stimulated depolarization currents and dielectric and dynamic mechanical behaviour of polyurethane networks prepared from poly(oxypropylene)diols or -triols and 4,4’-diphenylmethane diisocyanate were studied. While the frequency and temperature positions of mechanical and dielectric functions are predominantly determined by the concentration of polar urethane groups in the network chain, the equilibrium modulus correlates with network chain length. The effect of the chain polarity on the shape of loss permittivity vs. frequency curves is more pronounced in the low frequency region than in the high frequency one and is practically the same for stoichiometric and off-stoichiometric networks measured earlier.