Physical properties and elasticity behavior of amorphous polyurethane networks

A series of amorphous polyurethane networks have been prepared by reacting MDI (4,4'-diphenylmethane diisocyanate) with mixtures of a poly(oxyethylene) end -capped poly(oxypropylene) triol and a poly(oxyethylene) end-capped poly(oxypropylene) diol. The effects of crosslinking density on the physical properties and elasticity behavior of the polyurethane networks have been investigated by differential scanning calorimetry, DSC, tensile properties, single-edge notch, SEN, tear strength. The DSC results show that the glass transition temperature of the polyurethane networks increases slightly with increasing polyether diol content indicating that effect of urethane bond concentration outweighs that of crosslinking density. Composition affects the physical properties significantly. As the polyether diol content increases (the crosslinking density decreases), the tensile strength, elongation at break, tensile toughness and tear strength increase, but the initial modulus decreases. The tensile stress-strain data have been analyzed by the Mooney-Rivlin equation. As the polyether diol content increases, the crosslinking density decreases, and 2C(1), the modulus at very large deformation, and (2C(1) + 2C(2)), the modulus at very small deformation, decreases, as expected. As the polyether diol content increases, the polyurethane networks approach more to the phantom behavior.