The field of polyurethanes is rapidly growing in commercial importance, especially in foam and elastomer applications. This group of polymers includes a very broad range of chemical structures and molecular weights. In many cases polyurethanes are synthesized from a, oj polyester glycols or a, oj polyether glycols and diisocyanates so that the urethane groups are fewer in number than other functional groups (ester groups or ether groups) . This method of synthesis leads to a very wide range of polymer properties, adding interest to the studies of the relationship between structure and properties.