It is traditional to begin books about polyurethanes by defining the class of polymers that has come to be known as polyurethanes. Unlike olefin-based polymers (poly- ethylene, polypropylene, etc.), the uniqueness of polyurethane is that it results not from a specific monomer (ethylene, propylene, etc.), but rather from a type of reaction, specifically the formation of a specific chemical bond. Inevitably, the discussion in traditional books then progresses to the component parts, the produc- tion processes, and ultimately the uses. This is, of course, a logical progression inasmuch as most tests about polyurethanes are written for and by current or aspiring PUR (the accepted abbreviation for conventional polyurethanes).
