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.