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Poly(methyl methacrylate)
Poly(methyl methacrylate)
Poly(methyl methacrylate)
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Poly(methyl methacrylate)
Names
IUPAC name
Poly(methyl 2-methylpropenoate)
Other names
  • Poly(methyl methacrylate)
  • PMMA
  • Methyl methacrylate resin
  • Perspex
Identifiers
3D model (JSmol)
ChemSpider
  • None
ECHA InfoCard 100.112.313 Edit this at Wikidata
KEGG
UNII
  • CCC(C)(C(=O)OC)CC(C)(C(=O)OC)CC(C)(C(=O)OC)CC(C)(C(=O)OC)CC(C)(C(=O)OC)C
Properties
(C5H8O2)n
Molar mass Varies
Density 1.18 g/cm3[1]
−9.06×10−6 (SI, 22 °C)[2]
1.4905 at 589.3 nm[3]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)
Lichtenberg figure: high-voltage dielectric breakdown in an acrylic polymer block

Poly(methyl methacrylate) (PMMA) is a synthetic polymer derived from methyl methacrylate. It is a transparent thermoplastic used as an engineering plastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and brands Crylux, Walcast, Hesalite, Plexiglas, Acrylite, Lucite, PerClax, and Perspex, among several others (see below). This plastic is often used in sheet form as a lightweight or shatter-resistant alternative to glass. It can also be used as a casting resin, in inks and coatings, and for many other purposes.

It is often technically classified as a type of glass in that it is a non-crystalline vitreous substance, hence its occasional historic designation as acrylic glass.

History

[edit]

The first acrylic acid was created in 1843. Methacrylic acid, derived from acrylic acid, was formulated in 1865. The reaction between methacrylic acid and methanol results in the ester methyl methacrylate.

It was developed in 1928 in several different laboratories by many chemists, such as William R. Conn, Otto Röhm, and Walter Bauer, and first brought to market in 1933 by the German company Röhm & Haas AG (as of January 2019, part of Evonik Industries) and its partner and former U.S. affiliate Rohm and Haas Company under the trademark Plexiglas.[4]

Polymethyl methacrylate was discovered in the early 1930s by British chemists Rowland Hill and John Crawford at Imperial Chemical Industries (ICI) in the United Kingdom.[citation needed] ICI registered the product under the trademark Perspex. About the same time, chemist and industrialist Otto Röhm of Röhm and Haas AG in Germany attempted to produce safety glass by polymerizing methyl methacrylate between two layers of glass. The polymer separated from the glass as a clear plastic sheet, which Röhm gave the trademarked name Plexiglas in 1933.[5] Both Perspex and Plexiglas were commercialized in the late 1930s. In the United States, E.I. du Pont de Nemours & Company (now DuPont Company) subsequently introduced its own product under the trademark Lucite. In 1936 ICI Acrylics (now Lucite International) began the first commercially viable production of acrylic safety glass. During World War II both Allied and Axis forces used acrylic glass for submarine periscopes and aircraft windscreen, canopies, and gun turrets. Scraps of acrylic were also used to make clear pistol grips for the M1911A1 pistol or clear handle grips for the M1 bayonet or theater knives so that soldiers could put small photos of loved ones or pin-up girls' pictures inside. They were called "Sweetheart Grips" or "Pin-up Grips". Others were used to make handles for theater knives made from scrap materials.[6] Civilian applications followed after the war.[7]

Names

[edit]

Common orthographic stylings include polymethyl methacrylate[8][9] and polymethylmethacrylate. The full IUPAC chemical name is poly(methyl 2-methylpropenoate), although it is a common mistake to use "an" instead of "en".

Although PMMA is often called simply "acrylic", acrylic can also refer to other polymers or copolymers containing polyacrylonitrile. Notable trade names and brands include Walcast, Acrylite, Altuglas,[10] Astariglas, Cho Chen, Crystallite, Cyrolite,[11] Hesalite (when used in Omega watches), Lucite,[12] Optix,[11] Oroglas,[13] PerClax, Perspex,[11] Plexiglas,[11][14] R-Cast, and Sumipex.

Properties

[edit]
Skeletal structure of methyl methacrylate, the constituent monomer of PMMA
Pieces of Plexiglas taken from the windscreen of a German plane shot down during World War II

PMMA is a strong, tough, and lightweight material. It has a density of 1.17–1.20 g/cm3,[1][15] which is approximately half that of glass, which is generally, depending on composition, 2.2–2.53 g/cm3.[1] It also has good impact strength, higher than both glass and polystyrene, but significantly lower than polycarbonate and some engineered polymers. PMMA ignites at 460 °C (860 °F) and burns, forming carbon dioxide, water, carbon monoxide, and low-molecular-weight compounds, including formaldehyde.[16]

PMMA is an economical alternative to polycarbonate (PC) when tensile strength, flexural strength, transparency, polishability, and UV tolerance are more important than impact strength, chemical resistance, and heat resistance. Additionally, PMMA does not contain the potentially harmful bisphenol-A subunits found in polycarbonate and is a far better choice for laser cutting.[17] It is often preferred because of its moderate properties, easy handling and processing, and low cost. Non-modified PMMA behaves in a brittle manner when under load, especially under an impact force, and is more prone to scratching than conventional inorganic glass, but modified PMMA is sometimes able to achieve high scratch and impact resistance.

PMMA transmits up to 92% of visible light (3 mm (0.12 in) thickness),[18] and gives a reflection of about 4% from each of its surfaces due to its refractive index (1.4905 at 589.3 nm).[3] It filters ultraviolet (UV) light at wavelengths below about 300 nm (similar to ordinary window glass). Some manufacturers[19] add coatings or additives to PMMA to improve absorption in the 300–400 nm range. PMMA passes infrared light of up to 2,800 nm and blocks IR of longer wavelengths up to 25,000 nm. Colored PMMA varieties allow specific IR wavelengths to pass while blocking visible light (for remote control or heat sensor applications, for example).

PMMA swells and dissolves in many organic solvents; it also has poor resistance to many other chemicals due to its easily hydrolyzed ester groups. Nevertheless, its environmental stability is superior to most other plastics such as polystyrene and polyethylene, and therefore it is often the material of choice for outdoor applications.[20]

PMMA has a maximum water absorption ratio of 0.3–0.4% by weight.[15] Tensile strength decreases with increased water absorption.[21] Its coefficient of thermal expansion is relatively high at (5–10)×10−5 °C−1.[22]

The Futuro house was made of fibreglass-reinforced polyester plastic, polyester-polyurethane, and poly(methylmethacrylate); one of them was found to be degrading by cyanobacteria and Archaea.[23][24]

PMMA can be joined using cyanoacrylate cement (commonly known as superglue), with heat (welding), or by using chlorinated solvents such as dichloromethane or trichloromethane[25] (chloroform) to dissolve the plastic at the joint, which then fuses and sets, forming an almost invisible weld. Scratches may easily be removed by polishing or by heating the surface of the material. Laser cutting may be used to form intricate designs from PMMA sheets. PMMA vaporizes to gaseous compounds (including its monomers) upon laser cutting, so a very clean cut is made, and cutting is performed very easily. However, the pulsed lasercutting introduces high internal stresses, which on exposure to solvents produce undesirable "stress-crazing" at the cut edge and several millimetres deep. Even ammonium-based glass-cleaner and almost everything short of soap-and-water produces similar undesirable crazing, sometimes over the entire surface of the cut parts, at great distances from the stressed edge.[26] Annealing the PMMA sheet/parts is therefore an obligatory post-processing step when intending to chemically bond lasercut parts together.

In the majority of applications, PMMA will not shatter. Rather, it breaks into large dull pieces. Since PMMA is softer and more easily scratched than glass, scratch-resistant coatings are often added to PMMA sheets to protect it (as well as possible other functions).

Pure poly(methyl methacrylate) homopolymer is rarely sold as an end product, since it is not optimized for most applications. Rather, modified formulations with varying amounts of other comonomers, additives, and fillers are created for uses where specific properties are required. For example:

  • A small amount of acrylate comonomers are routinely used in PMMA grades destined for heat processing, since this stabilizes the polymer to depolymerization ("unzipping") during processing.
  • Comonomers such as butyl acrylate are often added to improve impact strength.
  • Comonomers such as methacrylic acid can be added to increase the glass transition temperature of the polymer for higher temperature use such as in lighting applications.
  • Plasticizers may be added to improve processing properties, lower the glass transition temperature, improve impact properties, and improve mechanical properties such as elastic modulus [27]
  • Dyes may be added to give color for decorative applications, or to protect against (or filter) UV light.
  • Fillers may be substituted to reduce cost.

Synthesis and processing

[edit]

Production

[edit]

PMMA is routinely produced by emulsion polymerization, solution polymerization, and bulk polymerization. Generally, radical initiation is used (including living polymerization methods), but anionic polymerization of PMMA can also be performed.[28]

The glass transition temperature (Tg) of atactic PMMA is 105 °C (221 °F). The Tg values of commercial grades of PMMA range from 85 to 165 °C (185 to 329 °F); the range is so wide because of the vast number of commercial compositions that are copolymers with co-monomers other than methyl methacrylate. PMMA is thus an organic glass at room temperature; i.e., it is below its Tg. The forming temperature starts at the glass transition temperature and goes up from there.[29] All common molding processes may be used, including injection molding, compression molding, and extrusion. The highest quality PMMA sheets are produced by cell casting, but in this case, the polymerization and molding steps occur concurrently. The strength of the material is higher than molding grades owing to its extremely high molecular mass. Rubber toughening has been used to increase the toughness of PMMA to overcome its brittle behavior in response to applied loads.

Recycling

[edit]

Plexiglass can be broken down with pyrolysis at a temperature of at least 400 °C (752 °F). The recovered monomers then are purified, but the costs and complexity have prevented this from becoming the norm.[30]

Another approach binds monomers to the ends of long polymer chains. Those monomers detach when heated, triggering the chain to disassemble, with monomer yields of up to 90%, although the presence of dyes reduce this number. However, polymers produced by this technology require special machinery and lack thermal stability.[30]

A third approach adds a chlorinated dichlorobenzene solvent to crushed Plexiglass. The mixture is heated to a modest 90–150 °C (194–302 °F) and exposed to ultraviolet light. The light splits a chlorine radical from the solvent, which breaks the polymer into monomers, which are purified via distillation, yielding virgin-grade stock. Even in the presence of additives, yields are 94 to 98%.[30]

Applications

[edit]
Close-up of pressure sphere of the bathyscaphe Trieste, with a single conical window of PMMA set into sphere hull. The very small black circle (smaller than the man's head) is the inner side of the plastic "window", only a few inches in diameter. The larger circular clear black area represents the larger outer side of the thick one-piece plastic cone "window".

Being transparent and durable, PMMA is a versatile material and has been used in a wide range of fields and applications such as rear-lights and instrument clusters for vehicles, appliances, and lenses for glasses. PMMA in the form of sheets affords to shatter resistant panels for building windows, skylights, bulletproof security barriers, signs and displays, sanitary ware (bathtubs), LCD screens, furniture and many other applications. It is also used for coating polymers based on MMA provides outstanding stability against environmental conditions with reduced emission of VOC. Methacrylate polymers are used extensively in medical and dental applications where purity and stability are critical to performance.[28]

Glass substitute

[edit]
10-meter-deep (33 ft) Monterey Bay Aquarium tank has acrylic windows up to 33 centimeters (13 in) thick to withstand the water pressure.
  • PMMA is commonly used for constructing residential and commercial aquariums. Designers started building large aquariums when poly(methyl methacrylate) could be used. It is less often used in other building types due to incidents such as the Summerland disaster.
  • PMMA is used for viewing ports and even complete pressure hulls of submersibles, such as the Alicia submarine's viewing sphere and the window of the bathyscaphe Trieste.
  • PMMA is used in the lenses of exterior lights of automobiles.[31]
  • Spectator protection in ice hockey rinks is made from PMMA.
  • Historically, PMMA was an important improvement in the design of aircraft windows, making possible such designs as the bombardier's transparent nose compartment in the Boeing B-17 Flying Fortress. Modern aircraft transparencies often use stretched acrylic plies.
  • Police vehicles for riot control often have the regular glass replaced with PMMA to protect the occupants from thrown objects.
  • PMMA is an important material in the making of certain lighthouse lenses.[32]
  • PMMA was used for the roofing of the compound in the Olympic Park for the 1972 Summer Olympics in Munich. It enabled a light and translucent construction of the structure.[33]
  • PMMA (under the brand name "Lucite") was used for the ceiling of the Houston Astrodome.

Daylight redirection

[edit]
Main article: Anidolic lighting
  • Laser-cut acrylic panels have been used to redirect sunlight into a light pipe or tubular skylight and, from there, to spread it into a room.[34] Their developers Veronica Garcia Hansen, Ken Yeang, and Ian Edmonds were awarded the Far East Economic Review Innovation Award in bronze for this technology in 2003.[35][36]
  • Attenuation being quite strong for distances over one meter (more than 90% intensity loss for a 3000 K source),[37] acrylic broadband light guides are then dedicated mostly to decorative uses.
  • Pairs of acrylic sheets with a layer of microreplicated prisms between the sheets can have reflective and refractive properties that let them redirect part of incoming sunlight in dependence on its angle of incidence. Such panels act as miniature light shelves. Such panels have been commercialized for purposes of daylighting, to be used as a window or a canopy such that sunlight descending from the sky is directed to the ceiling or into the room rather than to the floor. This can lead to a higher illumination of the back part of a room, in particular when combined with a white ceiling, while having a slight impact on the view to the outside compared to normal glazing.[38][39]

Medicine

[edit]
  • PMMA has a good degree of compatibility with human tissue, and it is used in the manufacture of rigid intraocular lenses which are implanted in the eye when the original lens has been removed in the treatment of cataracts. This compatibility was discovered by the English ophthalmologist Harold Ridley in WWII RAF pilots, whose eyes had been riddled with PMMA splinters coming from the side windows of their Supermarine Spitfire fighters – the plastic scarcely caused any rejection, compared to glass splinters coming from aircraft such as the Hawker Hurricane.[40] Ridley had a lens manufactured by the Rayner company (Brighton & Hove, East Sussex) made from Perspex polymerised by ICI. On 29 November 1949 at St Thomas' Hospital, London, Ridley implanted the first intraocular lens.[41]

In particular, acrylic-type lenses are useful for cataract surgery in patients that have recurrent ocular inflammation (uveitis), as acrylic material induces less inflammation.

  • Eyeglass lenses are commonly made from PMMA.
  • Historically, hard contact lenses were frequently made of this material. Soft contact lenses are often made of a related polymer, where acrylate monomers containing one or more hydroxyl groups make them hydrophilic.
  • In orthopedic surgery, PMMA bone cement is used to affix implants and to remodel lost bone.[42] It is supplied as a powder with liquid methyl methacrylate (MMA). Although PMMA is biologically compatible, MMA is considered to be an irritant and a possible carcinogen. PMMA has also been linked to cardiopulmonary events in the operating room due to hypotension.[43] Bone cement acts like a grout and not so much like a glue in arthroplasty. Although sticky, it does not bond to either the bone or the implant; rather, it primarily fills the spaces between the prosthesis and the bone preventing motion. A disadvantage of this bone cement is that it heats up to 82.5 °C (180.5 °F) while setting that may cause thermal necrosis of neighboring tissue. A careful balance of initiators and monomers is needed to reduce the rate of polymerization, and thus the heat generated.
  • In cosmetic surgery, tiny PMMA microspheres suspended in some biological fluid are injected as a soft-tissue filler under the skin to reduce wrinkles or scars permanently.[44] PMMA as a soft-tissue filler was widely used in the beginning of the century to restore volume in patients with HIV-related facial wasting. PMMA is used illegally to shape muscles by some bodybuilders.
  • Plombage is an outdated treatment of tuberculosis where the pleural space around an infected lung was filled with PMMA balls, in order to compress and collapse the affected lung.
  • Emerging biotechnology and biomedical research use PMMA to create microfluidic lab-on-a-chip devices, which require 100 micrometre-wide geometries for routing liquids. These small geometries are amenable to using PMMA in a biochip fabrication process and offers moderate biocompatibility.
  • Bioprocess chromatography columns use cast acrylic tubes as an alternative to glass and stainless steel. These are pressure rated and satisfy stringent requirements of materials for biocompatibility, toxicity, and extractables.

Dentistry

[edit]

Due to its aforementioned biocompatibility, poly(methyl methacrylate) is a commonly used material in modern dentistry, particularly in the fabrication of dental prosthetics, artificial teeth, and orthodontic appliances.

  • Acrylic prosthetic construction: Pre-polymerized, powdered PMMA spheres are mixed with a Methyl Methacrylate liquid monomer, Benzoyl Peroxide (initiator), and NN-Dimethyl-P-Toluidine (accelerator), and placed under heat and pressure to produce a hardened polymerized PMMA structure. Through the use of injection molding techniques, wax based designs with artificial teeth set in predetermined positions built on gypsum stone models of patients' mouths can be converted into functional prosthetics used to replace missing dentition. PMMA polymer and methyl methacrylate monomer mix is then injected into a flask containing a gypsum mold of the previously designed prosthesis, and placed under heat to initiate polymerization process. Pressure is used during the curing process to minimize polymerization shrinkage, ensuring an accurate fit of the prosthesis. Though other methods of polymerizing PMMA for prosthetic fabrication exist, such as chemical and microwave resin activation, the previously described heat-activated resin polymerization technique is the most commonly used due to its cost effectiveness and minimal polymerization shrinkage.
  • Artificial teeth: While denture teeth can be made of several different materials, PMMA is a material of choice for the manufacturing of artificial teeth used in dental prosthetics. Mechanical properties of the material allow for heightened control of aesthetics, easy surface adjustments, decreased risk of fracture when in function in the oral cavity, and minimal wear against opposing teeth. Additionally, since the bases of dental prosthetics are often constructed using PMMA, adherence of PMMA denture teeth to PMMA denture bases is unparalleled, leading to the construction of a strong and durable prosthetic.[45]

Art and aesthetics

[edit]
A Lexus LFA sculpture made out of Perspex
PMMA art by Manfred Kielnhofer
Kawai acrylic grand piano
Lucite Bangle Bracelet
  • Acrylic paint essentially consists of PMMA suspended in water; however since PMMA is hydrophobic, a substance with both hydrophobic and hydrophilic groups needs to be added to facilitate the suspension.
  • Modern furniture makers, especially in the 1960s and 1970s, seeking to give their products a space age aesthetic, incorporated Lucite and other PMMA products into their designs, especially office chairs. Many other products (for example, guitars) are sometimes made with acrylic glass to make the commonly opaque objects translucent.
  • Perspex has been used as a surface to paint on, for example by Salvador Dalí.
  • Diasec is a process which uses acrylic glass as a substitute for normal glass in picture frames. This is done for its relatively low cost, light weight, shatter-resistance, aesthetics and because it can be ordered in larger sizes than standard picture framing glass.
  • As early as 1939, Los Angeles-based Dutch sculptor Jan de Swart experimented with samples of Lucite sent to him by DuPont; De Swart created tools to work the Lucite for sculpture and mixed chemicals to bring about certain effects of color and refraction.[46]
  • From approximately the 1960s onward, sculptors and glass artists such as Jan Kubíček, Leroy Lamis, and Frederick Hart began using acrylics, especially taking advantage of the material's flexibility, light weight, cost and its capacity to refract and filter light.
  • In the 1950s and 1960s, Lucite was an extremely popular material for jewelry, with several companies specialized in creating high-quality pieces from this material. Lucite beads and ornaments are still sold by jewelry suppliers.
  • Acrylic sheets are produced in dozens of standard colors, most commonly sold using color numbers developed by Rohm & Haas in the 1950s.
See also: Acrylic embedment
Illustrative and secure bromine chemical sample used for teaching. The glass sample vial of the corrosive and poisonous liquid has been cast into an acrylic plastic cube

Methyl methacrylate "synthetic resin" for casting (simply the bulk liquid chemical) may be used in conjunction with a polymerization catalyst such as methyl ethyl ketone peroxide (MEKP), to produce hardened transparent PMMA in any shape, from a mold. Objects like insects or coins, or even dangerous chemicals in breakable quartz ampules, may be embedded in such "cast" blocks, for display and safe handling.

Other uses

[edit]
High-heeled footwear made of Lucite
An electric bass guitar made from poly(methyl methacrylate)
A Futuro house in Warrington, New Zealand
Vibrant, acrylic displays featuring images of materials
  • PMMA, in the commercial form Technovit 7200 is used vastly in the medical field. It is used for plastic histology, electron microscopy, as well as many more uses.
  • PMMA has been used to create ultra-white opaque membranes that are flexible and switch appearance to transparent when wet.[47]
  • Acrylic is used in tanning beds as the transparent surface that separates the occupant from the tanning bulbs while tanning. The type of acrylic used in tanning beds is most often formulated from a special type of polymethyl methacrylate, a compound that allows the passage of ultraviolet rays.
  • Sheets of PMMA are commonly used in the sign industry to make flat cut out letters in thicknesses typically varying from 3 to 25 millimeters (0.1 to 1.0 in). These letters may be used alone to represent a company's name and/or logo, or they may be a component of illuminated channel letters. Acrylic is also used extensively throughout the sign industry as a component of wall signs where it may be a backplate, painted on the surface or the backside, a faceplate with additional raised lettering or even photographic images printed directly to it, or a spacer to separate sign components.
  • PMMA was used in Laserdisc optical media.[48] (CDs and DVDs use both acrylic and polycarbonate for impact resistance).
  • It is used as a light guide for the backlights in TFT-LCDs.[49]
  • Plastic optical fiber used for short-distance communication is made from PMMA, and perfluorinated PMMA, clad with fluorinated PMMA, in situations where its flexibility and cheaper installation costs outweigh its poor heat tolerance and higher attenuation versus glass fiber.
  • PMMA, in a purified form, is used as the matrix in laser dye-doped organic solid-state gain media for tunable solid state dye lasers.[50]
  • In semiconductor research and industry, PMMA aids as a resist in the electron beam lithography process. A solution consisting of the polymer in a solvent is used to spin coat silicon and other semiconducting and semi-insulating wafers with a thin film. Patterns on this can be made by an electron beam (using an electron microscope), deep UV light (shorter wavelength than the standard photolithography process), or X-rays. Exposure to these creates chain scission or (de-cross-linking) within the PMMA, allowing for the selective removal of exposed areas by a chemical developer, making it a positive photoresist. PMMA's advantage is that it allows for extremely high resolution patterns to be made. Smooth PMMA surface can be easily nanostructured by treatment in oxygen radio-frequency plasma[51] and nanostructured PMMA surface can be easily smoothed by vacuum ultraviolet (VUV) irradiation.[51]
  • PMMA is used as a shield to stop beta radiation emitted from radioisotopes.
  • Small strips of PMMA are used as dosimeter devices during the Gamma Irradiation process. The optical properties of PMMA change as the gamma dose increases, and can be measured with a spectrophotometer.
  • Blacklight-reactive UV tattoos may use tattoo ink made with PMMA microcapsules and fluorescent dyes.[52]
  • In the 1960s, luthier Dan Armstrong developed a line of electric guitars and basses whose bodies were made completely of acrylic. These instruments were marketed under the Ampeg brand. Ibanez[53] and B.C. Rich have also made acrylic guitars.
  • Ludwig-Musser makes a line of acrylic drums called Vistalites, well known as being used by Led Zeppelin drummer John Bonham.
  • Artificial nails in the "acrylic" type often include PMMA powder.[54]
  • Some modern briar, and occasionally meerschaum, tobacco pipes sport stems made of Lucite.
  • PMMA technology is utilized in roofing and waterproofing applications. By incorporating a polyester fleece sandwiched between two layers of catalyst-activated PMMA resin, a fully reinforced liquid membrane is created in situ.
  • PMMA is a widely used material to create deal toys and financial tombstones.
  • PMMA is used by the Sailor Pen Company of Kure, Japan, in their standard models of gold-nib fountain pens, specifically as the cap and body material.
  • Optical fibers made of PMMA are used by Fiber optic drone.[55][56]

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Poly(methyl methacrylate)

View on Grokipedia
from Grokipedia
Poly(methyl methacrylate) (PMMA), also known as acrylic, Plexiglas, Perspex, or Lucite, is a synthetic, amorphous thermoplastic polymer derived from the free radical polymerization of the methyl methacrylate (MMA) monomer (C₅H₈O₂). It is a vinyl-based polymer renowned for its exceptional optical clarity (up to 92% light transmission, refractive index of 1.49), lightweight (density ~1.18 g/cm³), shatter resistance (impact strength up to 17 times that of glass), and rigidity (tensile strength 48–76 MPa, glass transition temperature 105–120 °C). PMMA is bioinert, hydrophobic, UV-stable, and resistant to dilute acids and bases, though susceptible to scratching and solvents like acetone; it softens around 100 °C without melting. The polymerization of MMA was first observed in 1877 by German chemists Wilhelm Rudolph Fittig and Rudolph Paul, but commercial development occurred in the 1930s. German chemist Otto Röhm's research on acrylic polymerization, starting with his 1901 doctorate, led to the founding of Röhm & Haas in 1907; under Dr. Walter Bauer's leadership, PMMA was developed in 1928, with the trademark PLEXIGLAS® registered in 1933 and industrial production beginning that year. Concurrently, British chemists and John Crawford at (ICI) developed PMMA in the early 1930s, leading to patents around 1931 and commercial production as Perspex by 1934. Widespread use expanded during for aircraft canopies and optical devices. PMMA is produced via free radical polymerization of MMA (derived industrially from routes like the process) and processed by casting, extrusion, or molding into sheets, rods, and components. Its versatility enables applications as a substitute in glazing, automotive parts, , and ; in for (since the 1950s), intraocular lenses, and ; and in aquariums, furniture, and protective barriers. Ongoing innovations include bio-based and recyclable variants to address environmental concerns.

History

Early discovery

The synthesis of the methyl methacrylate (MMA) monomer began with the preparation of methacrylic acid in 1865 by British chemists Edward Frankland and Baldwin F. Duppa, who obtained it through the hydrolysis of ethyl methacrylate derived from ethyl α-hydroxyisobutyrate treated with phosphorus trichloride. MMA itself was then produced via esterification of this methacrylic acid with methanol, yielding the clear liquid monomer essential for subsequent polymerization. In 1877, German chemists Rudolf Fittig and achieved the first known of MMA by heating the , resulting in a solid polymeric material that represented an early example of addition for acrylic esters. However, the reaction produced low-molecular-weight products with poor mechanical properties, often brittle and prone to upon heating, which restricted its scientific and practical interest at the time. Early 20th-century research advanced these findings through the work of German chemist Otto Röhm, who systematically explored acrylic polymerizations during his doctoral studies. In his 1901 thesis titled Über Polymerisationsprodukte der Acrylsäure, Röhm detailed the thermal polymerization of MMA and other acrylic esters, observing the formation of transparent, glass-like solids but encountering persistent issues such as incomplete conversion, variable chain lengths, and thermal instability that caused reversion to monomer. That same year, Röhm secured German patents for acrylic resins derived from these polymerizations, proposing their use in varnishes and adhesives as alternatives to natural gums, though the materials' fragility and processing difficulties delayed broader adoption. These foundational experiments highlighted the potential of PMMA as a transparent synthetic material but underscored key challenges, including the need for initiators to control reaction rates and improve yield, which limited initial applications to laboratory curiosities.

Commercial development

The commercialization of poly(methyl methacrylate) (PMMA) began with pioneering efforts in , where chemist Otto Röhm and his team at Röhm & Haas advanced practical techniques for producing clear, solid acrylic sheets. Building on Röhm's early research, including his 1901 doctoral dissertation on and subsequent patents such as a 1912 patent for vulcanizing acrylates, the breakthrough came in the late 1920s when researchers like Walter Bauer developed controlled casting methods between glass plates. This innovation enabled the scalable production of shatter-resistant PMMA sheets, culminating in the registration of Plexiglas on August 9, 1933, marking the material's entry into the market as a versatile alternative to glass. Parallel developments occurred in the , where chemists and John Crawford at (ICI) achieved the first clear PMMA sheet in 1933 through similar processes, leading to the Perspex the following year. These independent efforts by Röhm & Haas and ICI spurred rapid patenting and licensing agreements, with Röhm holding over 70 patents related to acrylic materials that facilitated international adoption. By the early , both companies had established production facilities, positioning PMMA for industrial applications beyond laboratory experiments. The onset of World War II dramatically accelerated PMMA's commercialization, as its lightweight, optically clear, and impact-resistant properties made it ideal for military uses by both Allied and Axis forces. It was extensively employed in aircraft windscreens, canopies for bombers like the British and , and gun turrets, as well as in submarine periscopes for enhanced visibility. Production scaled significantly to meet wartime demands, with Röhm & Haas and ICI prioritizing output for these applications, which highlighted PMMA's strategic value and drove process improvements in and . Following the war, PMMA transitioned to civilian markets, with post-1945 expansion into consumer products such as illuminated signage, architectural glazing, and . Röhm & Haas and ICI licensed the technology globally, leading to widespread adoption in the as production capacities grew to support emerging industries like automotive and furniture manufacturing. This period solidified PMMA's role as a key engineering , with annual output increasing from wartime peaks to meet burgeoning demand for durable, transparent materials.

Chemical identity

Structure

Poly(methyl methacrylate) (PMMA) is formed by the of its , (MMA, CAS 80-62-6), which has the molecular formula C₅H₈O₂ and the structural formula CH₂=C(CH₃)COOCH₃. The polymerizable carbon-carbon [CH₂=C(CH₃)-] in MMA enables , linking monomers into a long chain. The repeating unit of PMMA is -[CH₂C(CH₃)(COOCH₃)]-, resulting in the overall polymer formula (C₅H₈O₂)ₙ (CAS 9011-14-7), where n represents the . This unit consists of a carbon backbone with methyl and methoxycarbonyl () groups attached to every other carbon atom. PMMA is a linear , characterized by its unbranched chain structure and the presence of side groups that sterically hinder chain rotation and packing, contributing to its inherent rigidity and optical transparency. The stereochemistry of PMMA is defined by the tacticity of the chiral centers in the repeating units, which can be isotactic (all substituents on the same side of the chain), syndiotactic (alternating sides), or atactic (random arrangement). In commercial PMMA produced via free radical polymerization, the atactic configuration predominates, leading to a disordered chain arrangement that renders the polymer amorphous and incapable of crystallizing. This amorphous nature arises because the irregular tacticity prevents the close packing required for crystalline domains.

Nomenclature

Poly(methyl methacrylate), commonly abbreviated as PMMA, derives its name from the of its unit, . A systematic IUPAC name for the is poly(methyl 2-methylprop-2-enoate), reflecting the repeating linkage in its backbone derived from 2-methylprop-2-enoic acid (). In common usage, PMMA is frequently referred to as acrylic or acrylic due to its transparency and glass-like properties, terms that originated in the early when it was classified broadly among acrylic resins. Trade names have also proliferated since its commercialization, including Plexiglas® developed by Röhm & Haas in , Lucite® introduced by in the United States, Perspex® trademarked by Imperial Chemical Industries (ICI) in the , and Acrylite® used by various manufacturers such as Cyro Industries. The monomer, (MMA), has the IUPAC name methyl 2-methylprop-2-enoate and is synonymous with methacrylic acid methyl ester or , emphasizing its structure as the methyl ester of . Historically, the material was initially described under the umbrella term "" in the and during its early development, before polymer nomenclature standardized around "poly(methyl methacrylate)" in the mid-20th century to denote its specific chemical composition amid advancing .

Properties

Physical properties

Poly(methyl methacrylate) (PMMA) is a lightweight with a ranging from 1.17 to 1.20 g/cm³, which varies depending on the specific formulation and processing conditions; this value is approximately half that of and lower than that of transparent PVC sheets (1.35–1.45 g/cm³), contributing to its appeal in applications requiring reduced weight. Thermally, PMMA exhibits a glass transition temperature (Tg) that spans 85–165°C, with a typical value of 105°C for standard atactic PMMA, marking the point where the polymer transitions from a glassy to a rubbery state and loses significant rigidity. The coefficient of thermal expansion is 70–77 × 10⁻⁶ /K, indicating moderate dimensional changes with temperature fluctuations, while the softening point, often assessed via Vicat or heat deflection temperature, lies around 100–120°C, beyond which the material begins to deform under load. Mechanically, PMMA demonstrates solid performance in tension, with a tensile strength of 50–70 MPa and a of 2.4–3.3 GPa, reflecting its and ability to withstand pulling forces without excessive deformation in everyday conditions. However, it displays under impact, characterized by an impact strength of approximately 15–20 J/m for notched specimens, owing to its notch sensitivity where localized stress concentrations from imperfections or edges promote rapid crack propagation and rather than ductile yielding. Compared to transparent PVC sheets, PMMA provides higher surface hardness for improved scratch resistance and superior weather resistance with reduced yellowing. This combination of properties positions PMMA as a rigid yet impact-vulnerable suitable for controlled-load environments.

Chemical properties

Poly(methyl methacrylate) (PMMA) exhibits good chemical resistance to dilute acids, alkalis, and certain organic solvents such as aliphatic hydrocarbons, but is susceptible to ketones (e.g., acetone), chlorinated and aromatic hydrocarbons. It remains stable in contact with aqueous solutions of detergents, cleaners, dilute inorganic acids, alkalis, and aliphatic hydrocarbons such as oils and greases. However, PMMA is soluble in certain chlorinated hydrocarbons, including chloroform and dichloroethane, which can cause swelling or dissolution depending on concentration and exposure time. The hydrolytic stability of PMMA stems from its groups, which are resistant to neutral but susceptible to under strong basic conditions, leading to and chain breakdown. This resistance to ensures long-term durability in humid environments without significant degradation, though prolonged exposure to concentrated alkalis can compromise structural integrity. Thermal degradation of PMMA occurs primarily above 200°C through a mechanism known as unzipping, where the chain breaks down into its (MMA) units. This process is initiated by random scission at weak points, followed by sequential elimination of , resulting in near-quantitative yields of MMA under controlled heating. PMMA shows sensitivity to (UV) radiation, where absorption leads to chain scission and eventual yellowing due to the formation of chromophoric over extended exposure. This reduces molecular weight and can exacerbate physical through chemical aging. The effects are often mitigated by incorporating UV stabilizers or antioxidants as additives during synthesis. Regarding flammability, PMMA has an of approximately 460°C and is classified under the standard as HB, indicating it burns slowly in a horizontal orientation without self-extinguishing.

Optical properties

Poly(methyl methacrylate) (PMMA) exhibits high transparency in the , transmitting up to 92% of visible light through a 3 mm thick sample, surpassing the 90% transmission of standard and providing superior clarity over transparent PVC sheets, which show lower transmittance and increased yellowing propensity. This superior transmittance stems from its amorphous structure, which minimizes light scattering. The of PMMA is 1.4905 at 589.3 nm, corresponding to the sodium line. This value supports its use in optical components requiring precise bending. PMMA displays low dispersion, characterized by an of approximately 57, which indicates reduced compared to materials with lower Abbe values. In the ultraviolet-visible range, PMMA shows low absorption, with a cutoff around 300 nm, allowing effective transmission above this threshold for applications involving UV-Vis . Cast PMMA sheets exhibit minimal due to their isotropic nature, making them suitable for polarization-sensitive where stress-induced double must be avoided.

Synthesis and production

Monomer synthesis

The primary industrial route for synthesizing (MMA) is the (ACH) , which accounts for approximately 55% of global production as of 2024. Alternative routes, such as isobutene oxidation (~30-40%) and ethylene-based methods (~10-15%), make up the remainder. In this method, acetone reacts with (HCN) to form (ACH): \ce(CH3)2CO+HCN−>(CH3)2C(OH)CN\ce{(CH3)2CO + HCN -> (CH3)2C(OH)CN} The ACH intermediate is then treated with concentrated sulfuric acid to produce methacrylamide sulfate, followed by esterification with methanol to yield MMA and ammonium bisulfate as a byproduct: \ce(CH3)2C(OH)CN+H2SO4−>(CH3)2C(OSO3H)C(O)NH2\ce{(CH3)2C(OH)CN + H2SO4 -> (CH3)2C(OSO3H)C(O)NH2} \ce(CH3)2C(OSO3H)C(O)NH2+CH3OH−>CH2=C(CH3)COOCH3+NH4HSO4\ce{(CH3)2C(OSO3H)C(O)NH2 + CH3OH -> CH2=C(CH3)COOCH3 + NH4HSO4} This overall process achieves an approximate yield of 90% based on acetone, though it generates significant quantities of ammonium sulfate waste (often from bisulfate processing), estimated at up to 1.5–2 tons per ton of MMA produced. The ACH process was first commercialized in in 1933 as a variant of chemistry and became the dominant method by the 1950s, supplanting earlier routes such as those involving and HCN due to higher efficiency and scalability. Alternative routes include the direct oxidation of isobutene, where isobutene is first oxidized to methacrolein and then to (MAA), followed by esterification with to form MMA; this process, introduced in in the 1980s, offers yields up to 70–80% but requires specialized catalysts to minimize byproducts like . -based routes, such as the - process, involve the reaction of with and to form , followed by condensation with and subsequent dehydration and esterification to MMA; these methods, developed in the , aim to reduce reliance on HCN and have been commercialized for their lower waste profiles, though they represent a smaller share of production.

Polymerization methods

Poly(methyl methacrylate) (PMMA) is synthesized through the polymerization of (MMA) , primarily via chain-growth mechanisms that form the repeating unit [-CH₂-C(CH₃)(COOCH₃)-]ₙ from n CH₂=C(CH₃)COOCH₃. The most widely adopted approach is free radical , which proceeds through , , and termination steps. In free radical , typically involves of peroxides such as benzoyl peroxide or azo compounds like 2,2'-azobisisobutyronitrile (AIBN) to generate primary radicals that add to the vinyl double bond of MMA. occurs via successive addition of MMA monomers to the growing radical , forming a head-to-tail structure with the group pendant on the alpha carbon. Termination takes place through combination of two radicals to form a single or involving hydrogen abstraction, leading to polymers with molecular weights typically in the range of 10⁵–10⁶ Da. Bulk polymerization, a form of free radical polymerization, employs undiluted MMA , resulting in high-purity, transparent PMMA suitable for applications like sheets and rods. This method requires careful to manage the and prevent autoacceleration, where increases limit radical termination and accelerate rates. It is commonly used for producing "optical" grade PMMA due to minimal impurities from solvents or dispersants. Emulsion and polymerizations utilize water as a to moderate the reaction heat and produce particulate forms of PMMA, such as beads or . In , MMA is dispersed in water with and water-soluble initiators like persulfates, forming micelles where occurs, yielding submicron particles with narrow size distributions. involves mechanical agitation to suspend droplets stabilized by dispersants, often initiated by oil-soluble peroxides, resulting in larger beads (10–1000 μm) after conversion. These methods facilitate industrial-scale production of PMMA powders or dispersions for coatings and composites. Advanced techniques, such as anionic living polymerization, enable precise control over molecular weight and polydispersity for specialized applications. This method uses strong bases like alkyl initiators or zincates in polar solvents at low temperatures (-78°C), allowing chain growth without termination to achieve number-average molecular weights (Mₙ) from 10⁴ to 10⁶ Da with polydispersity indices (Đ) as low as 1.1. Living anionic polymerization of MMA often produces syndiotactic PMMA with tailored , contrasting the atactic structure from free radical methods.

Industrial production

Global production of poly(methyl methacrylate) (PMMA) reached approximately 3.2 million metric tons annually as of 2024, with major producers including Mitsubishi Chemical Corporation, Röhm GmbH, , and Sumitomo Chemical Co., Ltd., which together account for a significant share of the market. Industrial-scale PMMA manufacturing primarily relies on techniques, with continuous processes favored for producing extrusion-grade due to their efficiency in achieving high throughput and uniform quality. In continuous , is fed into a series of reactors where conversion progresses steadily, contrasting with batch methods used for specialized cast sheets that allow for controlled, intermittent cycles but lower overall output. Additives such as rubber-based impact modifiers are integrated during the stage to enhance , typically comprising 5-20% by weight depending on the desired properties. The production process consumes approximately 105 MJ of energy per kilogram of PMMA resin, predominantly from non-renewable sources, with ongoing efforts to optimize reactor designs and heat recovery systems to reduce this footprint. in industrial settings emphasizes molecular weight distribution, targeting a polydispersity index (PDI) of around 2, assessed via (GPC) to ensure consistent performance in downstream applications.

Processing techniques

Casting and molding

Poly(methyl methacrylate) (PMMA) is commonly formed into sheets, rods, and complex shapes through casting and molding techniques that leverage free radical or processing of pre-polymerized resin. In free radical casting, particularly cell casting, a syrup of partially polymerized with initiators such as benzoyl is poured between two plates separated by a flexible to form a cell of desired thickness, typically 1–50 mm for optical sheets. The filled cells are stacked vertically and placed in an , where occurs at controlled temperatures of 40–80°C over several hours, allowing staged curing to manage the approximately 21% volume shrinkage inherent to the reaction. This batch process yields high optical clarity with minimal internal stresses, as the slow cure avoids rapid heat buildup, though cycle times extend to hours depending on sheet thickness. For rods or more intricate shapes, similar free radical casting uses tubular molds or adjustable forms, with the monomer-initiator mixture polymerized under controlled conditions to achieve uniform properties. Shrinkage is mitigated by initiator selection and temperature gradients, ensuring dimensional stability in the final product. Injection molding processes PMMA pellets, first dried at 80–90°C for 3–4 hours to remove , which is critical due to the material's hygroscopic nature. The dried pellets are melted in a barrel at 180–250°C and injected at pressures of 80–140 MPa into a mold maintained at 40–80°C, allowing for rapid filling of precision cavities for parts like lenses. Holding pressure of 40–60 MPa follows to compensate for the low shrinkage of 0.2–0.8%, ensuring high dimensional accuracy and , with cycle times typically under a minute for thin-walled components. This method excels in producing intricate, high-precision items with excellent optical quality when molds are vented properly to avoid defects. Compression molding suits thicker blocks or custom shapes, where pre-weighed PMMA pellets or powder are placed in an open heated mold at 180–220°C, then compressed under 10–20 MPa until the material flows and fills the cavity. The closed mold is held at for annealing, minimizing residual stresses, before cooling under pressure to prevent warping. This technique offers advantages in handling larger charges and achieving uniform density in bulky items, though it requires longer cycles than injection molding. Overall, these methods provide versatility: casting prioritizes superior optical properties and stress-free sheets for demanding applications, while injection and compression enable efficient production of precise or robust forms from industrially produced PMMA resin.

Extrusion and forming

Extrusion of poly(methyl methacrylate) (PMMA) involves feeding pellets into a single-screw extruder with an L/D ratio of at least 30:1, typically using a two-stage screw design to ensure uniform melting and mixing. The material is heated in barrel zones progressing from 140–200°C at the feed end to 200–240°C at the die, achieving a melt temperature of 205–230°C, after which it is forced through a streamlined die to form continuous profiles such as sheets, films, or tubes. For sheet production, thicknesses range from 0.05 mm to 6 mm, with the extrudate passing through a calibration unit and cooled via a three-roll stack with independent temperature controls to maintain dimensional stability and surface quality. Tube extrusion employs similar parameters but uses internal cooling mandrels for precise sizing. Output rates can reach up to 1000 kg/h depending on screw diameter and line configuration. Co-extrusion enables the production of multi-layer PMMA sheets by simultaneously extruding compatible materials, such as a recycled PMMA core sandwiched between virgin PMMA outer layers for enhanced UV protection and weather resistance. This process integrates UV-absorbing additives in the cap layers, improving longevity for outdoor applications while maintaining optical clarity, and is commonly used for solid or multi-wall sheets up to several millimeters thick. Thermoforming follows extrusion by reheating the produced sheets to 150–180°C in an until pliable, then clamping the sheet over a mold and applying full (up to approximately 1 bar) to draw it into the mold cavity for shaping into items like domes, signs, or enclosures. Mold temperatures are maintained at 70–80°C to prevent sticking and ensure even cooling, with plug-assist techniques used for deeper draws to minimize thinning. The formed part is then cooled under restraint to avoid distortion. Potential drawbacks in extrusion and forming include the formation of flow lines or melt due to uneven heating, shear stresses, or inadequate die design, which can degrade surface aesthetics if not mitigated by proper annealing. High processing speeds may also induce orientation stresses, reducing impact resistance in the final product. Post-forming annealing relieves residual stresses by heating the shaped PMMA to 80–85°C for 1–2 hours (depending on thickness), followed by controlled slow cooling at 10–20°C per hour to ambient temperature, preventing or warping during service. This step is essential for maintaining structural integrity in load-bearing or environmentally exposed applications.

Applications

Glass substitute

Poly(methyl methacrylate) (PMMA), commonly known as acrylic, serves as an effective glass substitute in structural applications due to its advantageous physical properties. With a density of 1.17–1.20 g/cm³, PMMA is approximately half the weight of traditional soda-lime (2.5 g/cm³), reducing structural loads and improving energy efficiency in installations such as windows and panels. Additionally, PMMA exhibits impact resistance approximately 5–17 times greater than conventional , making it shatter-resistant and safer by breaking into dull-edged pieces rather than sharp shards. These attributes enable PMMA to replace in scenarios requiring durability without the risk of , while maintaining high optical transmission comparable to for clear visibility. Key applications of PMMA as a substitute include large-scale aquariums, windows, and bullet-resistant glazing. In aquariums, PMMA panels provide the necessary strength to withstand water pressure; for instance, the Georgia Aquarium's Ocean Voyager exhibit features a large acrylic panel measuring 2 feet (610 mm) thick to house safely. For , PMMA sheets are widely used in windows and canopies due to their lightweight nature (half that of ) and shatter resistance (11 times greater than ), enhancing and safety in commercial, military, and . In security contexts, laminated PMMA configurations offer bullet-resistant protection, with multi-layered acrylic sheets tested to UL levels 1–3, providing a transparent barrier that stops projectiles without spalling. PMMA sheets for these uses are typically fabricated via , yielding thicknesses from 0.5 mm to 50 mm to suit varying structural demands, such as thin panels for windows or thicker ones for high-pressure environments. To address surface vulnerabilities, anti-scratch coatings, such as hard-coat or mar-resistant finishes, are applied to extruded sheets, enhancing abrasion resistance for prolonged exposure in high-traffic areas. Despite these benefits, PMMA has limitations that must be considered for substitution. It possesses lower inherent scratch resistance compared to , necessitating protective coatings to prevent surface damage from daily wear. Without UV stabilizers, prolonged exposure to light can cause yellowing and degradation, reducing transparency over time; stabilized formulations mitigate this for outdoor applications. PMMA holds a significant , approximately 30%, in the transparent plastics segment for glazing, driven by its balance of clarity, strength, and cost-effectiveness.

Optics and lighting

Poly(methyl methacrylate) (PMMA) plays a crucial role in optical applications due to its high transparency, often exceeding 92% transmission in the . In systems, PMMA prismatic sheets are widely employed as diffusers in LED fixtures, featuring microstructured surfaces such as inverted textures that redirect over 90% of incident uniformly across the output area, minimizing and hotspots while enhancing luminous . These sheets improve overall fixture performance by diffusing evenly, making them ideal for commercial and architectural where uniform illumination is essential. PMMA is also molded into precision lenses and prisms for and applications, leveraging its ease of fabrication via injection molding for complex geometries. In cameras, PMMA lenses provide clear, lightweight with high clarity, suitable for consumer and professional devices. For solar concentrators, PMMA-based Fresnel lenses achieve concentration ratios up to 1000x by focusing sunlight onto photovoltaic cells or thermal receivers, enabling efficient in concentrated photovoltaics (CPV) systems. These designs benefit from PMMA's low cost and optical quality, though they require achromatic configurations to mitigate at high concentrations. In daylighting systems, edge-lit PMMA panels utilize to redirect natural light from skylights into building interiors, distributing illumination uniformly without mechanical trackers. These panels guide sunlight along the material's length via TIR, emitting it through patterned surfaces to reduce energy use for artificial in deep-plan spaces. For data transmission, doped PMMA forms graded-index plastic optical fibers (GI-POF) that support short-distance communications up to 100 m at 1 Gbps, offering a cost-effective alternative to fibers in home networking and automotive applications. Recent advancements post-2020 include microstructured PMMA films for enhanced backlights in displays and lighting, where optimized patterns on light guide plates achieve superior uniformity and efficiency through precise light extraction control. These films, fabricated via techniques like dotting or molding, support high-brightness applications while maintaining low power consumption.

Medical uses

Poly(methyl methacrylate) (PMMA) serves as a critical in , primarily as for fixing implants during procedures like and replacements. This acrylic , when mixed with antibiotics such as gentamicin or , provides mechanical stability while releasing the antimicrobial agents to prevent or treat prosthetic joint infections. Globally, surgeries number over 1 million annually, with PMMA used in a significant portion to fill voids and anchor prostheses effectively. In , PMMA is employed to fabricate intraocular lenses (IOLs) for , where the clouded natural lens is replaced to restore vision. These rigid PMMA lenses offer excellent optical clarity and , with many remaining functional for over 20 years post-implantation due to their inert nature and resistance to degradation. Although traditional PMMA IOLs require larger incisions compared to foldable alternatives, their durability makes them suitable for patients needing long-term correction. For dental applications, heat-cured PMMA is a standard material in prosthetics like complete and partial , valued for its ease of processing, aesthetic properties, and sufficient mechanical strength under oral conditions. Its biocompatibility is rigorously assessed under standards, including tests that confirm cell viability above 70% in direct contact assays, ensuring safety for prolonged intraoral use. PMMA's versatility extends to drug delivery systems, where porous scaffolds enable controlled release of therapeutics, such as antibiotics, directly into defects or sites. These constructs, often created by incorporating porogens like or carboxymethylcellulose, achieve sustained over days to weeks without compromising structural integrity, aiding in the management of osseous infections during orthopedic interventions. Recent advancements in the 2020s have focused on enhancing PMMA's through modifications like composites for scaffolds. For instance, PMMA blended with or forms porous structures that support and proliferation while promoting bone regeneration, addressing limitations in bioactivity for load-bearing applications. These developments, including nanofiber-reinforced variants, show promise in preclinical models for improved .

Other uses

Poly(methyl methacrylate) (PMMA) serves as a filament material in fused deposition modeling (FDM) 3D printing, enabling the rapid prototyping of complex structures, particularly those derived from medical imaging data. Layer adhesion in these FDM processes is optimized by maintaining the interface temperature between successive layers above the glass transition temperature (Tg) of PMMA, which ensures proper bonding without excessive deformation. Post-printing cooling below Tg further stabilizes the structure while promoting interlayer strength. In artistic applications, PMMA's transparency and ease of make it suitable for creating intricate sculptures, such as structural prototypes in where precise cuts prevent in rod-like elements. It is also employed in high-voltage discharge experiments to produce Lichtenberg figures, branching patterns formed by injection into acrylic blocks, resulting in decorative artworks and scientific mementos. For , PMMA sheets are widely used in illuminated displays due to their optical clarity, diffusion capabilities, and weather resistance, allowing efficient LED integration for backlit and edge-lit signs. Within the automotive sector, PMMA finds use in taillights and rear lighting assemblies, where its high light transmission and clarity enhance visibility. It is also incorporated into masks and instrument panels, benefiting from impact-modified grades that improve stress crack resistance while retaining . These modified variants provide enhanced toughness for interior and exterior trim components under mechanical stress. In , PMMA acts as an electrical insulator in protective panels, leveraging its of 35 to 40 kV/mm to prevent short circuits and ensure mechanical stability. Its application extends to touchscreens, where PMMA forms durable display covers with high scratch and impact resistance, contributing to longer device lifespans in . Recent advancements include PMMA's role in , such as the fabrication of three-dimensional photonic crystals using close-packed PMMA spheres embedded in oxide matrices like SiO2 and TiO2, which exhibit tunable for advanced photonic devices. In sustainable materials, post-2022 research has focused on waste PMMA into durable composites through and reactive blending with like PLA, facilitated by catalysts such as MgO, to create eco-friendly alternatives with improved mechanical performance.

Sustainability

Recycling methods

Poly(methyl methacrylate) (PMMA) waste can be recovered through mechanical , which involves grinding discarded sheets or products into small particles and then re-extruding them into pellets for in lower-grade applications. This process is straightforward and energy-efficient but is limited to approximately 3–5 cycles before significant degradation occurs, reducing molecular weight and optical clarity due to and shear stresses during processing. The of PMMA facilitates this initial recovery, though contamination from additives or mixed plastics often necessitates prior sorting. Chemical recycling methods offer higher-quality recovery by breaking PMMA back into its monomer, (MMA), enabling closed-loop production of virgin-like material. , a technique, heats PMMA waste to 400–500°C in an inert atmosphere, yielding up to 90% MMA with over 90% purity after . Solvent-based approaches use chlorinated solvents at lower temperatures (90–150°C) combined with UV or visible light initiation to achieve , recovering 94–98% MMA even from or contaminated scraps. The core reaction is represented as: [−\ceCH2−C(CH3)(COOCH3)−]n→n\ceCH2=C(CH3)COOCH3+heat\left[ -\ce{CH2-C(CH3)(COOCH3)-} \right]_n \rightarrow n \ce{CH2=C(CH3)COOCH3} + \text{heat} This unzipping mechanism predominates under controlled conditions, minimizing side products like methanol or char. Industrial implementations demonstrate the feasibility of these methods in closed-loop systems. For instance, Polyvantis (formerly Röhm) operates a Europe-wide program partnering with fabricators to collect PMMA offcuts, mechanically and chemically recycling them into proTerra-grade products with high monomer recovery rates approaching 95%. Similarly, the MMAtwo consortium has piloted extrusion-based depolymerization, purifying crude MMA to enable repolymerization for end-of-life products. Despite these advances, challenges persist, including the need for effective separation of contaminants like dyes or copolymers, which can lower yields, and the energy-intensive nature of , which requires optimized reactors to minimize emissions.

Environmental impact

Poly(methyl methacrylate) (PMMA) is non-biodegradable and persists in landfills for hundreds of years, similar to other synthetic polymers, due to its stable that resists microbial degradation. If fragmented through or mechanical stress, PMMA contributes to microplastic in terrestrial and aquatic environments, where particles smaller than 5 mm accumulate and affect ecosystems. The production of PMMA has a of approximately 3.7–4.8 kg CO₂ per kg, primarily from energy-intensive processes and feedstock derivation. This is higher than that of flat glass, a common substitute material, which emits about 2.15 kg CO₂ per kg during . As a petroleum-derived , PMMA production consumes roughly 1.5–2 barrels of per ton, reflecting the reliance on fossil feedstocks like acetone and hydrocyanic acid for synthesis. Sustainability initiatives are addressing these impacts through bio-based alternatives, such as pilot plants developed in the that produce from renewable plant-derived materials, potentially reducing dependence on fossil resources. At end-of-life, global PMMA recycling rates remain low at less than 10%, limiting reductions in virgin material demand, though European (EPR) schemes have increased recovery and supported a modest 10% substitution of recycled content in some applications.

Safety considerations

Health effects

Poly(methyl methacrylate) (PMMA) is derived from (MMA) monomer, which exhibits moderate . The oral LD50 of MMA in rats is approximately 6–10 g/kg, indicating low acute lethality, but it acts as an irritant to the skin, eyes, and upon exposure. Skin contact can cause redness and , while eye exposure leads to severe and potential corneal damage. Inhalation of MMA vapors may result in coughing, , and, in sensitive individuals, respiratory linked to cases. The International Agency for Research on Cancer (IARC) classifies MMA as Group 3, not classifiable as to its carcinogenicity to humans, based on inadequate evidence in humans and animals. In contrast, the polymerized form, PMMA, is largely inert and demonstrates low cytotoxicity, supporting its biocompatibility in medical implants and devices despite the monomer's risks. However, inhalation of PMMA dust generated during machining or fabrication can irritate the respiratory tract, causing symptoms such as coughing and throat discomfort, though systemic effects are minimal. During surgical procedures involving PMMA-based bone cement, residual MMA monomer release can trigger bone cement implantation syndrome, manifesting as hypotension in 5-30% of cases depending on severity and procedure, as reported in recent studies (as of 2024), alongside potential hypoxemia and cardiac arrhythmias. This hemodynamic instability arises from embolization and monomer toxicity, but its incidence is low with modern techniques. Occupational exposure to MMA primarily affects workers in and , where sensitization to MMA, leading to , has been reported in 15-40% of dental personnel, with skin manifestations in up to 40% of technicians. The (OSHA) sets a (PEL) of 100 ppm for MMA vapor over an 8-hour workday to minimize these risks. PMMA itself poses fewer occupational hazards beyond . Mitigation strategies for both MMA and PMMA exposures emphasize like local exhaust ventilation and administrative measures, supplemented by such as gloves, goggles, and respirators. Neither MMA nor PMMA bioaccumulates in biological systems, reducing long-term persistence concerns. These safety profiles enable PMMA's continued use in medical applications, where benefits outweigh controlled risks.

Regulatory aspects

Poly(methyl methacrylate) (PMMA) for medical applications, such as , is classified as a Class II medical device by the U.S. (FDA), requiring premarket notification under 510(k) and adherence to special controls outlined in the guidance document for PMMA bone cement. This classification, specified in 21 CFR § 888.3027, ensures the device's safety and effectiveness for use in arthroplastic procedures to fix prosthetic implants to living . In the , the monomer (MMA), essential for PMMA production, is registered under Regulation (EC) No 1907/2006, with an indicative of 50 ppm (205 mg/m³) as an 8-hour time-weighted average to mitigate potential health risks from . While no specific emission restrictions below 205 mg/m³ are mandated under REACH for MMA, the requires risk assessments and safe use information for downstream users in industrial and professional settings. PMMA meets flammability standards for plastics under ASTM D635, the test method for rate of burning in a horizontal orientation, and is classified as HB (horizontal burning), indicating slow burning without significant dripping or rapid flame spread. This classification aligns with HB requirements for non-halogenated materials used in electrical and consumer products, confirming PMMA's suitability for applications where moderate fire resistance is needed. For transportation, is regulated as a hazardous material under UN 1247, classified as a in Class 3 (packing group II), requiring specific labeling, packaging, and documentation per international agreements like the UN Model Regulations and U.S. DOT 49 CFR. In contrast, solid PMMA products, such as sheets or molded parts, are generally non-hazardous for transport unless containing residual above threshold levels. Internationally, PMMA products undergo UV stability testing per ISO 4892-2, which simulates outdoor exposure using xenon-arc lamps to evaluate degradation resistance in applications like glazing and . Compliance with this standard ensures long-term performance and regulatory acceptance in global markets for weather-exposed uses.

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