Formation, structure and physical properties of ordered polyurethane networks

The thermal and dynamic mechanical behaviour of ordered stoichiometric as well as off-stoichiometric polyurethane networks based on mesogenic diol - 6,6'-[ethylenebis(1,4-phenyleneoxy)]dihexanol (D), 2(4)-methyl-1,3-phenylene diisocyanate (DI) and poly(oxypropylene) triol (T) is reviewed. The effects of various initial molar ratios of the reactive groups ([OH] T /[NCO] DI /[OH] D ) and of the ordered or isotropic state of the diol on the critical gel structure at the sol-gel transition and a power-law mechanical behaviour is discussed. The effects of amount of mesogenic diol in the elastically active network chains (EANCs) on the conformational rearrangements required for ordering, the concentration of permanent physical interactions (trapped entanglements) and on the intensity of the slow relaxation process in the rubbery region are shown.