Polymethylmethacrylate (PMMA) is a polymer that behaves like a thermoplastic material and belongs to the group of acrylates. It is transparent and transmits close to 100% visible light, thus outperforming glass in many respects.
PMMA is a lighter material than glass, it is more resistant to impacts and can be used in constructions that require a transparent material of great thickness; such is the case of large aquariums that use PPMA blocks up to 33 cm thick.
PMMA was synthesized in 1930 by English chemists Rowland Hill and John Crawford, who registered the material under the name Perspex. Later, in 1933, the German chemist Otto Röhm managed to manufacture PMMA by a different method, a material he called Plexiglas.
PMMA is synthesized by the polymerization of methyl methacrylate (its monomer), a molecule with a vinyl structure of the formula C 5 O 2 H 8 . The polymerization of the monomer is produced by the free radical method, producing amorphous polymers without a crystalline structure.
Structure of polymethylmethacrylate
PMMA is a polymer formed by the polymerization of methyl methacrylate monomer:
This vinyl polymerizes by the method of free radicals, as occurs with polyvinyl chloride (PVC).
The polymers produced by this method are characterized in that the substituent or pendant groups are located randomly along the polymer chain.
Consider the top image. In it, the -OCOCH 3 groups are all on the same side; but in reality, they are alternated: not all point to the same side. This, plus the differences between the average lengths or sizes of the PMMA chains, causes that crystals cannot form; and therefore it is amorphous and is referred to as an “atactic” polymer.
The presence of the methyl group in methyl methacrylate prevents PMMA from forming a crystalline structure and from being able to freely rotate around the CC bonds. Thus, PMMA is considered an amorphous thermoplastic.
Poly (methyl 2-methylpropeonate)
Poly (methyl methacrylate) (PMMA), methyl methacrylate resin, Perspex, Plexiglas, Lucite and other names.
(C 5 O 2 H 8 ) n
This formula is that of the monomer (methyl methacrylate) and n represents the number of monomers present in PMMA.
The molar mass depends on the number of monomers or subunits that the polymer has, with the molar mass of methyl methacrylate equal to 100.12 g / mol (on average).
1.18 g / cm 3
160 ° C. Although there are reports of the melting point of 220 ºC, perhaps due to differences in the polymers studied.
Refractive index (n D )
1.4905 at a wavelength of 589.3 nm.
PMMA burns at 460ºC releasing carbon dioxide, water, carbon monoxide and other compounds such as formaldehyde.
Soluble in tetrahydrofuran, toluene, cyclohexanone, chloroform and ethyl acetate, as well as in other organic solvents due to the presence in the polymer of methyl groups that are easily solvated. However, it is insoluble in alcohols, aliphatic hydrocarbons and in water.
PMMA undergoes complete hydrolysis by sulfuric acid (H 2 SO 4 ). It is also hydrolyzed, although more slowly, by hydrochloric acid and hydroiodic acid.
Behavior in light
PMMA is resistant to sunlight due to its resistance to UV light. It has a transmission to visible light of 92% and filters ultraviolet light with a wavelength less than 300 nm.
PMMA sheets are passed through by infrared light with a wavelength up to 2800 nm. But it blocks infrared light with a wavelength greater than 25,000 nm.
It is stable at room temperature and incompatible with strong oxidizing agents.
PMMA is more resistant to impacts than glass, although its resistance is lower than that of polycarbonate.
PMMA is synthesized from propylene, an unsaturated hydrocarbon obtained by distillation of petroleum . Propylene reacts with benzene, producing isopropylbenzene or cumene. Subsequently, this compound is oxidized to cumene hydroperoxide.
Then the cumene hydroperoxide is treated with acid to produce an acetone, which is converted into methyl methacrylate, the monomer of PMMA.
The polymerization is carried out hot by placing in a container a mixture of the monomer, and an initiator of the free radical polymerization reaction, usually a peroxide, such as potassium peroxydisulfate. The reaction is exemplified by the following equation:
Additionally, an emulsifier is added, for example, sodium stearate and water, producing solid PMMA.
Uses / applications of PMMA
PMMA is present in many human activities, ranging from the construction of houses and transport vehicles, to artistic expressions, such as painting.
Due to its transparency to visible light and its resistance to ultraviolet light, PMMA is used in the construction of windows, doors, canopies, panels, etc. In addition, PMMA directs visible light in order to obtain natural lighting in homes and other buildings.
PMMA also provides good thermal insulation that allows it to be used in greenhouse construction. The polymer has the property of being able to be used with a thickness of up to 33 cm, without losing its ability to transmit light unlike glass.
This allows PMMA to be used in the construction of large aquariums, which due to the large volumes of water they contain, experience great pressure on their walls.
PMMA is used in car windows and lights. In airplanes it is used in windows, panels and canopies. Meanwhile, in submarines and bathiscatos it is used for observing the exterior.
Additive for lubricants
Lubricating oils and hydraulic fluids become viscous when they experience a drop in temperature. The addition of PMMA facilitates proper operation of the machines up to a temperature of -100 ºC, as it prolongs their fluidity.
PMMA is used in the manufacture of conventional corrective lenses and hard contact lenses, not soft contact lenses. The polymer is used to make intraocular lenses to replace the crystalline, natural eye lens damaged in the condition known as cataracts.
PMMA cement is used in orthopedic surgery for implant fixation and bone remodeling. The function of the bone cement is not to glue, but to fill in the free space between the bone and the inserted prosthesis, which allows better function.
PMMA is also used in the form of microspheres to fill the soft tissue underlying the skin, a procedure used in cosmetic surgery to reduce scars and wrinkles.
PMMA is used to make teeth, as well as dentures, and long-lasting parts.
PMMA is used in the production of acrylic paints, present in paintings. Likewise, it is used in the elaboration of the frames of the paintings. And as if it weren’t enough, the polymer is used in the making of guitars, pianos and other musical instruments.
Due to its high light transmission, PMMA is used in television screens, LCD screens, laptop computers, telephone screens, and electronic equipment. It is also used in solar panels due to its resistance to ultraviolet light and its transmission of visible light.