STRUCTURE AND ELASTICITY OF POLYURETHANE NETWORKS BASED ON POLY(BUTADIENE) DIOL, 4,4'-DIPHENYLMETHANE DIISOCYANATE AND POLY(OXYPROPYLENE) TRIOL

Relations between structure and equilibrium mechanical properties of p olyurethane networks based on poly(butadiene) diol, 4,4'-diphenylmetha ne diisocyanate (MDI) and poly(oxypropylene) triol (POPT) prepared at various initial ratios of reactive groups were studied. An inhomogeneo us structure of the networks was revealed by small-angle X-ray scatter ing. The microdomains consist of POPT molecules crosslinked with MDI a nd they have a diameter of about 4-5 nm. The characteristic distance o f microdomains is about 9 nm. The poor mutual miscibility of the react ion components and the existence of hydroxyl group association in the reaction mixture are the probable reasons for microdomain formation. T he strain dependence of the equilibrium elastic force obeyed the Moone y-Rivlin equation. The experimental moduli of dry and equilibrium swol len samples were higher than those calculated for the affine limit of the Flory junction fluctuation model on the assumption of a homogeneou s network formation.