History of polyurethanes

The pioneering work on polyurethane polymers was carried out by Otto Bayer and his co-workers in 1937 at IG Farben’s laboratories in Leverkusen, Germany. They recognized that the use of the polyaddition principle to produce polyurethanes from liquid diisocyanates and liquid polyether or polyester diols seemed to point to special opportunities, especially compared to existing plastics that were made by polymerizing olefins or by polycondensation. The new monomer combination also circumvented existing patents issued by Wallace Carothers on polyesters. Initially, the work focused on the production of flexible fibers and foams. With development limited by WWII (when PUs were applied on a limited scale as aircraft coatings), it was not until 1952 that polyisocyanates became commercially available. Commercial production of flexible polyurethane foam began in 1954, based on toluene diisocyanate (TDI) and polyester polyols. The invention of these foams (initially called imitation Swiss cheese by the inventors) was due to water accidentally introduced into the reaction mixture.

These materials were also used to produce rigid foams, chewing gum, and elastomers. Linear fibers were produced from hexamethylene diisocyanate (HDI) and 1,4-butanediol (BDO). The first commercially available polyether polyol, poly (tetramethylene ether) glycol), was introduced by DuPont in 1956 by polymerizing tetrahydrofuran. BASF and Dow Chemical introduced less expensive polyalkylene glycols the following year, 1957. These polyether polyols offered technical and commercial advantages such as low cost, ease of handling, and better hydrolytic stability; and it quickly replaced polyester polyols in the manufacture of polyurethane products. Another PU pioneer was the Mobay corporation. In 1960, more than 45,000 tons of flexible polyurethane foams were produced. As the decade progressed, the availability of inexpensive chlorofluoroalkane blowing agents, polyether polyols, and methylenediphenyl diisocyanate (MDI) heralded the development and use of rigid polyurethane foams as insulation materials with high performance, stability, and combustion characteristics than those based on in TDI. In 1967, rigid urethane-modified polyisocyanurate foams were introduced, offering even better thermal stability and flammability resistance to low-density insulation products.

Also during the 1960s, safety components inside the car, such as instruments and door panels, were produced by filling thermoplastic liners with semi-rigid foam. In 1969, Bayer AG exhibited an all-plastic car in Dusseldorf, Germany. Parts of this car were manufactured using a new process called RIM, Reaction Injection Molding. RIM technology uses the high pressure impact of liquid components followed by the rapid flow of the reaction mixture into the mold cavity. Large parts, such as car fascia and body panels, can be molded this way. Polyurethane RIM evolved into a number of different products and processes. The use of diamine chain extenders and trimerization technology gave poly (urethane urea), poly (urethane isocyanurate) and RIM polyurea. The addition of fillers, such as ground glass, mica, and processed mineral fibers resulted in RRIM, Reinforced RIM, which provided improvements in flexural modulus (stiffness) and thermal stability. This technology enabled the production of the first plastic-bodied automobile in the United States, the Pontiac Fiero, in 1983. Further improvements to the flex modulus were obtained by incorporating glass mats previously placed in the RIM mold cavity, also known as SRIM. , or structural RIM. In the early 1980s, flexible water blown microcellular foam was used to mold gaskets for panel and radial seal air cleaners in the automotive industry. Since then, rising energy prices and the desire to remove PVC plastisol from automotive applications have greatly increased market share. More expensive raw materials are offset by a significant decrease in part weight and, in some cases, the removal of metal end caps and filter housings.

High-fill polyurethane elastomers and more recently unfilled polyurethane foams are now used in high-temperature oil filter applications. Polyurethane foam (including foam rubber) is often made by adding small amounts of volatile materials, so-called blowing agents, to the reaction mixture. These simple volatile chemicals produce important performance characteristics, primarily thermal insulation. In the early 1990s, due to its impact on ozone depletion, the Montreal Protocol led to a considerable reduction in the use of many chlorine-containing blowing agents, such as trichlorofluoromethane (CFC-11). Other haloalkanes, such as the hydrochlorofluorocarbon 1,1-dichloro-1-fluoroethane (HCFC-141b), were used as temporary substitutes until their elimination according to the IPPC directive on greenhouse gases in 1994 and the directive on volatile organic compounds (VOCs) . of the EU in 1997 (See: Haloalkanes). In the late 1990s, the use of blowing agents such as carbon dioxide, pentane, 1,1,1,2-tetrafluoroethane (HFC-134a), and 1,1,1,3,3-pentafluoropropane (HFC-245fa ) became more widespread in North America and the EU, although chlorinated blowing agents continued to be used in many developing countries.

Based on existing polyurethane spray coating technology and polyetheramine chemistry, extensive development of two-component polyurea elastomers took place in the 1990s. Their rapid reactivity and relative insensitivity to moisture make them useful coatings for large-area projects such as secondary containment, well and tunnel liners, and tank liners. Excellent adhesion to concrete and steel is obtained with the proper primer and surface treatment. During the same period, a new two-component polyurethane and polyurethane-polyurea hybrid elastomer technology was used to enter the market for spray-on-site loading bed liners. This technique for coating pickup truck beds and other cargo compartments creates a durable, abrasion-resistant composite with the metal substrate and eliminates the corrosion and brittleness associated with thermoplastic bed liners. The use of polyols derived from vegetable oils to make polyurethane products began to gain attention starting in 2004, partly due to rising petrochemical raw material costs and partly due to a greater public desire for environmentally friendly products. environment. One of the most vocal supporters of these polyurethanes made from natural oil polyols is Ford Motor Company.