FORMATION AND PROPERTIES OF URETHANE DIACETYLENE SEGMENTED BLOCK COPOLYMERS

Two types of urethane-diacetylene segmented block copolymers have been prepared using a one-step bulk polymerization process. By varying the length of the polyether soft segments using different polyols, copolymers with different physical properties have been produced. In one case a copolymer which is rubbery at room temperature has been prepared by using a polyoxypropylene diol with a molecular weight of 1000 g mol-1. The other material obtained using a polyoxypropylene diol with a molecular weight of 400 g mol-1 is glassy at room temperature. It has been found that the phase-separated hard domains will undergo thermally induced, solid-state cross-polymerization of the diacetylene groups in the domains. This is found to lead to a modification of the physical properties of the materials involving a change in colour, and an increase in the thermal stability, glass transition temperatures and the Young's moduli of the copolymers. The mechanical properties of the polymers have been interpreted using the Takayanagi mechanical models and the average modulus of the cross-polymerized hard segments has been determined to be about 5 GPa. Well-defined Raman spectra characteristic of conventional polymers have been obtained from the copolymers and it is found that the position of the Raman bands shifts to lower frequency during tensile deformation. This is shown to be due to deformation taking place within the hard segments and it is demonstrated that Raman spectroscopy offers a unique way of determining hard segment deformations in these materials.