Acrylic glass
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Chemical name
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poly(methyl 2-methylpropenoate)
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Chemical formula
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(C5O2H8)n
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Synonyms
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polymethylmethacrylate
PMMA poly(methyl methacrylate) methyl methacrylate resin |
Molecular mass
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varies
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CAS number
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9011-14-7
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Density
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1.19 g/cm3
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Melting point
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n/a (amorphous polymer)
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[Glass transition tempreture]
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~118 °C
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[Beta transition tempreture]
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~60 °C
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Boiling point
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200.0 °C
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Refractive index
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1.492 (λ=589.3 nm)
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V-number
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55.3
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SMILES
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C[C](C)C(=O)OC
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Polymethyl methacrylate (PMMA) or poly(methyl 2-methylpropenoate) is thesynthetic
polymer of methyl methacrylate. This thermoplastic and transparentplastic is sold by the tradenames Plexiglas, Perspex, Plazcryl,Acrylite,Acrylplast, Altuglas, and Lucite and is commonly called acrylic glass or simplyacrylic. The material
was developed in 1928 in various laboratories and was
brought to market in 1933 by the German Company Rohm and Haas (GmbH
& Co. KG).
The material is often used as an alternative to glass. Differences in the
properties of the two materials include:
§
PMMA is lighter: its density (1190 kg/m3) is about half
that of glass.
§
PMMA does not shatter
§
PMMA is softer and more easily scratched than glass. This can be
overcome with scratch-resistant coatings.
§
PMMA can be easily formed, by heating it to 100 degrees Celsius.
§
PMMA transmits more light (92% of visible light) than glass.
§
Unlike glass, PMMA does not filter UV (ultraviolet)
light. PMMA transmits UV light, at best intensity, down to 300 nm. Some manufacturers coat their PMMA with UV films to add
this property. On the other hand, 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 air,
PMMA ignites at 460° C and burns completely to form only carbon dioxide and water.
If hydrogen atoms are substituted for the methyl groups (CH3)
attached to the C atoms, poly(methyl acrylate) is produced. 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.
§
Injection moulding grade
Molar Mass ~ 60,000
§
Cast grade
Molar Mass ~ 10^6 Production: monomer + initiator are heated
together forming a syrup-----> syrup is poured in a mould(low temp for long
duration)eg: 50 degrees C for few hours method used to make sheets and
rods.(simple shapes)
PMMA is used for instance in the lenses of automobile
running-lights. The spectator protection in ice hockey stadiums
is made of PMMA, as are the largest windows and aquariums in the
world. 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.
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.
PMMA has a good degree of compatibilty 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, in which acrylate
monomers are used that contain one or more hydroxyl groups to 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 together these yield
a dough-like cement that gradually hardens in the body. Surgeons can judge the
curing of the PMMA bone cement by the smell of MMA in the patient's breath.
Athough 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. <ref>American Journal of
Neuroradiology, 23:601-604, April 2002.</ref> 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. <ref>Miller, Review of Orthopaedics,
4th Edition, p 129.</ref>
Dentures are
often made of PMMA. In cosmetic surgery, tiny PMMA microspheres
suspended in some biological fluid are injected under the skin to reduce
wrinkles or scars permanently.
Artificial nails are made of acrylic too.
Modern furniture makers, especially in the 1960s and
1970s, looking to give their products a space age feel
also incorporated Lucite and other PMMA products into their designs, especially
in office chairs. Many other products (for example, guitars) are sometimes made
with acrylic glass, giving otherwise-ordinary objects a transparent or
futuristic look.
Recently, a blacklight-reactive tattoo ink using PMMA microcapsules has
surfaced. The technical name is BIOMETRIX System-1000, and it is marketed under
the name "Chameleon Tattoo Ink". This ink is reportedly quite 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 (cross-linking) within the PMMA, allowing for the selective
removal of exposed areas by a chemical developer. PMMA's advantage lies in that
it allows for extremely high resolution (nanoscale) patterns to be made. It is
an invaluable tool in nanotechnology.