Poly(methyl methacrylate)

Poly(methyl methacrylate), often referred to as PMMA, is a synthetic resin. Its properties—transparency and rigidity—make it a common substitute for glass. It is an acrylic polymer and is commonly known by the trademark names Lucite, Perspex, and Plexiglas. In powder form, it is known as Diakon.

Discovery and Development

PMMA and all acrylic plastics are polymers. Polymers get their name from the Greek words poly (many) and meros (a part). Polymers are made of many molecules linked together. These chains may contain thousands of molecules. The first plastic polymer was developed in 1869. Early applications included Bakelite, which was used to make radios, telephones, and household goods such as buttons.

Chemists in England and Germany were both working on developing PMMA during the 1930s. British chemists Rowland Hill and John Crawford registered their discovery as Perspex. Otto Rohm polymerized methyl methacrylate between sheets of glass; it separated from the glass as a sheet of clear plastic, which Rohm called Plexiglas. E.I. du Pont de Nemours & Company in the United States also developed PMMA, which the company (now DuPont) trademarked as Lucite.

PMMA was first employed during World War II in manufacturing bubble canopies for gun turrets and windows for aircraft. PMMA was highly valued because many service members were badly injured or killed by shattering glass; when acrylic shattered, the injuries were much less severe. It was also used for submarine periscopes. Rohm and his friend, Otto Haas, formed a company that produced Plexiglass parts such as windows for military vehicles.

The Rohm and Haas Company had continued to explore uses of acrylic polymers and had developed it for use as an oil additive and molding powder. When the war ended, military production ceased and the company focused on commercial uses for acrylic polymers. Many veterans were starting families and looking for homes during the late 1940s and 1950s. This construction boom included an increased demand for paint. Solvent-based paints available at the time were flammable, smelly, and difficult to clean off brushes and other tools. Rohm and Haas scientists developed an aqueous acrylic emulsion process that used the acrylic polymer as a binder to hold the components of paint together. The resulting water-based paints were easy to apply, durable, and could be cleaned up using water. By the 1970s, the company had improved acrylic paints so much that they outsold oil-based exterior paints in the United States.

Other advances in acrylic polymers were also being developed during the war. Early contact lenses were made of glass or a combination of glass and plastic. They were not gas permeable and could be worn for only a few hours because the eye needs oxygen. In 1948, a California optician introduced contact lenses made of PMMA. PMMA contact lenses were thinner and lighter. Though not gas permeable, they moved slightly with each blink, allowing oxygen-rich tears to bathe the eye even under the lenses. For the first time, individuals could wear contact lenses for sixteen hours a day or longer. Soon, many more consumers were wearing contact lenses. Rigid PMMA lenses often provide greater vision clarity than soft lenses; however, many consumers prefer more comfortable gas-permeable lenses.

What Is PMMA?

PMMA is manufactured using propylene, which is refined from crude oil. A reaction of propylene and benzene forms cumene (isopropylbenzene), which is oxidized to cumene hydroperoxide. After being treated with acid, it becomes acetone. A further three-step process changes the acetone to flammable methyl methacrylate. Methyl methacrylate may be polymerized, which means many of its molecules link together, by using free-radical initiators. This creates solid PMMA. It is completely recyclable; high heat returns it to liquid methyl methacrylate, which may be refined and reused to make more PMMA.

PMMA has several clear advantages over glass. Because it is shatter resistant (it is often described as shatterproof), it is often used for windows, skylights, and aircraft canopies. While thick glass is often difficult to see through, the view through PMMA remains clear even when it is a foot thick. It is about 90 percent transparent, which is clearer than glass. For this reason, PMMA is used in large aquariums, where the windows and walls are under enormous pressure from the water. One window made of PMMA at the Monterey Bay Aquarium in California is 16.6 m long, 5.5 m high, and 33 cm thick (54 ft long, 18 ft high, 13 in thick). PMMA also withstands weather and ultraviolet radiation for many years with little change.

PMMA is often used in shields around hockey rinks, to make lighted signs, in cell phone lenses and touch screens, and for automobile light lenses. Many optical fibers used in endoscopy and telecommunications are made of PMMA because of its usefulness in transmitting light. Because it takes and holds color well, it is also used for one-piece shower components and countertops. It has been used to make furniture, jewelry, false eyes and teeth, and even as bone cements.

Its lightweight but strong characteristics make PMMA an important factor in manufacturing energy-efficient vehicles. The light weight—two times lighter than glass—reduces fuel consumption of automobiles and boats. At the same time, PMMA fabrication uses less energy than many other materials. While glass must be heated for forming, PMMA may be formed cold. It also has a very long life—up to twenty years in some cases—and is not affected by saltwater or other conditions. PMMA resists chemicals, scratches, and many conditions that affect other materials.

Among its many uses, PMMA is also added to many hydraulic fluids and lubricating oils. It helps prevent these fluids from becoming viscous in very cold weather.

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