'Polymethyl methacrylate' ('PMMA') or poly (methyl 2-methylpropanoate) is the
synthetic polymer of
methyl methacrylate. This
thermoplastic and
transparent plastic is sold by the tradenames 'Plexiglas', 'Limacryl', 'R-Cast', 'Perspex', 'Plazcryl', 'Acrylex', 'Acrylite', 'Acrylplast', 'Altuglas', 'Polycast' and 'Lucite' and is commonly called 'acrylic glass' or simply 'acrylic'.
The material was developed in 1928 in various laboratories and was brought to market in
1933 by
Rohm and Haas Company.
Properties
Structure of the PMMA polymer
The material is often used as an alternative to
glass. Differences in the properties of the two materials include
★ PMMA is less dense; its
density can range from 1150-1190 kg/m
3. This is less than half the density of glass which ranges 2400 to 2800 kg/m
3.
★ PMMA has a higher
impact strength than glass and does not shatter but instead breaks into large dull pieces.
★ PMMA is softer and more easily scratched than glass. This can be overcome with scratch-resistant coatings.
★ PMMA is typically processed at a lower temperature than glass, just 240-250 °C.
★ PMMA
transmits more light (up to 93% of visible light) than conventional glass.
[1] However, there exist special optical grades of glass that can transmit up to 98% of light.
[2]
★ Unlike glass, PMMA does not filter
ultraviolet (UV) light. PMMA transmits UV light down to 300
nm. Some manufacturers
[3] add a coating to PMMA sheets to make them absorb UV light. PMMA molecules have great UV stability compared to
polycarbonate.
★ PMMA allows
infrared light of up to 2800
nm wavelength to pass. IR of longer wavelengths, up to 25,000 nm, are essentially blocked. Special formulations of colored PMMA exist to allow specific IR wavelengths to pass while blocking
visible light (for
remote control or heat sensor applications, for example).
PMMA can be joined using
cyanoacrylate cement (so-called "Superglue"), or by using liquid
di- or
trichloromethane to dissolve the plastic at the joint which then fuses and sets, forming an almost invisible
weld. PMMA can also be easily polished to restore cut edges to full transparency.
To produce 1
kg of PMMA, about 2 kg of
petroleum is needed. In the presence of oxygen, PMMA ignites at 460°
C and burns completely to form only
carbon dioxide and
water.
Related polymer poly(methyl acrylate)
The polymer of methyl acrylate, PMA or poly(methyl acrylate), is similar to poly(methyl methacrylate), except for the lack of methyl groups on the backbone carbon chain.
[4] PMA is a soft white rubbery material that is softer than PMMA because its long polymer chains are thinner and smoother and can more easily slide past each other.
Uses
PMMA or Acrylic is a versatile material and has been used in a wide range of fields and applications.
Impact resistant substitute for glass
★ PMMA Acrylic glass is commonly used for constructing residential and commercial
aquariums.
★ PMMA is used in the lenses of exterior lights of automobiles.
[5]
★ The spectator protection in
ice hockey stadiums is made of PMMA.
★
Motorcycle helmet visors
★ Police vehicles for
riot control often have the regular glass replaced with acrylic to protect the occupants from thrown objects.
★ Lucite was used for windows on the
Bathyscaphe Trieste which descended to the lowest point on the ocean floor, the
Challenger Deep.
★ Polycast acrylic sheet is the most widely used material in aircraft transparencies (windows). In applications where the aircraft is pressurized, stretched acrylic is used.
Medical technologies and implants
★ PMMA has a good degree of compatibility with
human tissue, and can be used for replacement
intraocular lenses in the
eye when the original lens has been removed in the treatment of
cataracts. Hard
contact lenses are 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
orthopaedics, PMMA bone cement is used to affix implants and to remodel lost bone. It is supplied as a powder with liquid
methyl methacrylate (MMA). When mixed these yield a dough-like cement that gradually hardens. Surgeons can judge the curing of the PMMA bone cement by pressing their thumb on it. 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.
[6] Bone cement acts like a
grout and not so much like a glue in
arthroplasty. Although sticky, it primarily fills the spaces between the prosthesis and the bone preventing motion. It has a
Young's modulus between
cancellous bone and
cortical bone. Thus it is a load sharing entity in the body not causing
bone resorption.
[7]
★
Dentures are often made of PMMA, and can be colour-matched to the patient's teeth. In
cosmetic surgery, tiny PMMA microspheres suspended in some biological fluid are injected under the skin to reduce wrinkles or scars permanently.
Artistic and aesthetic uses
★
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 esthetic incorporated Lucite and other PMMA products into their designs, especially office chairs. Many other products (for example, guitars) are sometimes made with acrylic glass, giving otherwise ordinary objects a transparent or futuristic look.
★ Perspex has been used as a surface to paint on, for example by
Salvador Dalí.
★ Occasionally used as a
glass substitute in
picture framing, due to its relatively inexpensive cost, light weight, and shatter-resistant nature, as well as the fact that it can be ordered in larger sizes than standard picture-framing glass. Conventional glass may or may not be preferred.
★ From approximately the 1960s onward, sculptors and glass artists began using acrylics, especially taking advantage of the material's flexibility, light weight, cost and its capacity to refract and filter light.
Other uses
★ The material is used to produce
laserdiscs, and sometimes also for
DVDs, but the more expensive
polycarbonate (also used for
CDs) has better properties when exposed to moisture.
★ Used for the "bubble" on the front of submarines such as
Alicia (submarine).
★ Artificial fingernails are made of acrylic.
★ 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 [8] and
BC Rich have also made acrylic guitars.
★ Recently a
blacklight-reactive
tattoo ink using PMMA
microcapsules was developed. This ink is reportedly safe for use, and claims to be
Food and Drug Administration approved for use on wildlife that may enter the food supply.
★ 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 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 (nanoscale) patterns to be made. It is an invaluable tool in
nanotechnology.
★ Small strips of PMMA are used as
dosimeter devices during the
Gamma Irradiation process. The optical density of PMMA changes as the Gamma dose increases and can be measured with a
spectrophotometer.
★ It is used as a light guide for the backlights in
TFT-LCDs.
★
Ludwig-Musser makes a line of acrylic drums called Vistalites. They are well known as being used by Led Zeppelin drummer
John Bonham.
See also
★ Other transparent plastics:
polystyrene,
polycarbonate
External links
★
Cast Acrylic Data Sheet
References
1. MatWeb material property database - Overview of General Purpose Acrylic molding resin
2. http://www.matweb.com/search/SpecificMaterial.asp?bassnum=CGLACO23 MatWeb material property database - High optical transmitance glass
3. Altuglas International Plexiglas UF-3 UF-4 and UF-5 sheets
4. Polymethyl acrylate and polyethyl acrylate, Encyclopædia Britannica
5. Kutz, Myer, Handbook of Materials Selection. John Wiley & Sons 2002. pg 341
6. American Journal of Neuroradiology, 23:601-604, April 2002.
7. Miller, Review of Orthopaedics, 4th Edition, p 129.
8. http://www.ibanezregister.com/Gallery/js/gal-js2k.htm and http://ibanez.com/eg/guitar.aspx?m=JEM20TH
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