Formation, structure and physical properties of ordered polyurethane networks

The thermal and dynamic mechanical behaviour of ordered stoichiometric as w ell 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 effect s 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 behavio ur is discussed. The effects of amount of mesogenic diol in the elastically active network chains (EANCs) on the conformational rearrangements require d for ordering, the concentration of permanent physical interactions (trapp ed entanglements) and on the intensity of the slow relaxation process in th e rubbery region are shown.