Polyurethane

Lore & Background

The new polymers had some advantages over existing plastics made by polymerizing olefins or by polycondensation, and were not covered by patents obtained by Wallace Carothers on polyesters. Early work focused on the production of fibers and flexible foams, and PUs were applied on a limited scale as aircraft coating during World War II. These materials were also used to produce rigid foams, gum rubber, and elastomers. Linear fibers were produced from hexamethylene diisocyanate (HDI) and 1,4-butanediol (BDO). Polyether polyols were cheaper, easier to handle, and more water-resistant than polyester polyols. Union Carbide and Mobay, a U.S. Monsanto/Bayer joint venture, also began making polyurethane chemicals. The availability of chlorofluoroalkane blowing agents, inexpensive polyether polyols, and methylene diphenyl diisocyanate (MDI) allowed polyurethane rigid foams to be used as high-performance insulation materials. During the 1960s, automotive interior safety components, such as instrument and door panels, were produced by back-filling thermoplastic skins with semi-rigid foam. Parts of this car, such as the fascia and body panels, were manufactured using a new process called reaction injection molding (RIM). Starting in the early 1980s, water-blown microcellular flexible foams were used to mold gaskets for automotive panels and air-filter seals, replacing PVC polymers. In the early 1990s, the Montreal Protocol restricted the use of many chlorine-containing blowing agents due to their impact on ozone depletion. By the late 1990s, blowing agents such as carbon dioxide, pentane, 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1,1,3,3-pentafluoropropane (HFC-245fa) were widely used in North America and the EU, although chlorinated blowing agents remained in use in many developing countries.

Reader's Guide

Polyurethane represents a significant class of polymers due to its chemical versatility and wide range of applications. Unlike many other common polymers, polyurethanes can be tailored by varying the starting materials—diisocyanates and polyols—as well as additives and processing conditions, resulting in products ranging from soft, flexible foams used in cushions and mattresses to rigid foams for thermal insulation, and from durable elastomers for shoe soles to fibers like spandex. The ability to produce both thermosetting and thermoplastic forms further expands their utility. The development of polyurethane foams, which account for the majority of production, revolutionized industries such as automotive seating, insulation, and bedding. The introduction of reaction injection molding (RIM) in the late 1960s enabled the production of large, complex plastic parts for automobiles, exemplified by the Pontiac Fiero. Environmental regulations, particularly the Montreal Protocol, drove innovation in blowing agents, shifting from ozone-depleting chlorofluorocarbons to alternatives like carbon dioxide and hydrofluorocarbons.

Did You Know?

• In the early 1990s, the Montreal Protocol restricted the use of chlorine-containing blowing agents like CFC-11 due to their impact on ozone depletion.