PMMA ( Polymethyl methacrylate )

 

Acrylic glass
 
Chemical name poly (methyl 2-methylpropenoate)
Chemical formula (C5O2H8)n
Synonyms polymethylmethacrylate
PMMA
poly (methyl methacrylate)
methyl methacrylate resin
Molecular mass varies
CAS number 9011-14-7
Density 1.19 g/cm
Melting point 130-140C (265-285F)
Boiling point 200.0 C
Refractive index 1.492 (λ=589.3 nm)
V-number 55.3
SMILES C[C](C)C(=O)OC

 
Disclaimer and references
Polymethyl methacrylate (PMMA) or poly (methyl 2-methylpropenoate) is the synthetic polymer of methyl methacrylate. This thermoplastic and transparent plastic is sold by the tradenames Plexiglas, Perspex, Plazcryl, Acrylite, Acrylplast, Altuglas, 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
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 has a higher impact strength than glass and will not shatter.
PMMA is softer and more easily scratched than glass. This can be overcome with scratch-resistant coatings.
PMMA is typically processed at 240-250 degrees Celsius.
PMMA transmits more light (up to 93% of visible light) than glass.
Unlike glass, PMMA does not filter ultraviolet (UV) 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 Carbon 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.

Uses
 
Structure of methyl methacrylate, the monomer that makes up PMMA
Underwater restaurant Ithaa, five meters below sealevel, is encased in PMMAPMMA 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.
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 he ocean floor, the Challenger Deep.
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. 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.

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.
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 Dal.
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.
Artificial fingernails are made of acrylic.
Recently a blacklight-reactive tattoo ink using PMMA microcapsules was developed. The technical name is BIOMETRIX System-1000, and it is marketed under the name "Chameleon Tattoo Ink". 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 (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.