Polymethyl methacrylate (PMMA) or poly (methyl 2-methylpropenoate) is the synthetic polymer of methyl methacrylate. This thermoplastic and transparentplastic is sold by the tradenames Plexiglas, Perspex, Plazcryl, Acrylite, Acrylplast, Altuglas, R-Cast, 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.
Contents
1Properties
2Uses
3See also
4References
5External links
Properties
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/m3. This is less than half the density of glass which ranges 2400 to 2800 kg/m3.
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 degrees Celsius.
PMMA transmits more light (up to 93% of visible light) than glass.[1]
Unlike glass, PMMA does not filter ultraviolet (UV) light. PMMA transmits UV light down to 300 nm. Some manufacturers[2] 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 nmwavelength 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.
The polymer of methyl acrylate, poly(methyl acrylate), is similar to poly(methyl methacrylate), except for the lack of methyl groups on the backbone carbon chain. This soft white rubbery material is softer than PMMA because its long polymer chains are thinner and smoother and can more easily slide past each other.
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. [4] 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. [5]
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, its light weight, and its shatter-resistent nature, as well as the fact that it can be ordered in larger sizes than standard picture-framing glass. Generally conventional glass is preferred, however.
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)
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 coatsilicon 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. PMMA's advantage is that it allows for extremely high resolution (nanoscale) patterns to be made. It is an invaluable tool in nanotechnology.
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