The Structure of Polyurethane Elastomers.

Polyurethane elastomers derive their properties from phase separation into hard urethane and soft polyether or polyester domains. We have used x-ray diffraction and conformational analysis to determine the structure of the hard domains in MDIdiolpolyester polyurethanes. A new structure has been developed for MDIbutandiol C4 hard segments, based on the following approaches. Solution of structures of two MDI derivatives showed the basic features of the polymer conformation, packing, and hydrogen bonding. Better quality x-ray patterns allowed determination of the unit cell. Potential energy conformational analysis was applied to polyurethanes for the first time. The results point to a fully extended polyMDIbutandiol chain linked to its neighbors in a stabillizing two-dimensional hydrogen bonding network. This work was expanded to the polyurethanes prepared using the C2-C8 homologous series of diols. The even diol series except C2 adopt fully extended structures like that for the C4 polymer. In contrast the odd diol series adopt higher energy contracted conformations, probably in order to form intermolecular hydrogen bonds.