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/cm3
Melting point	n/a (amorphous polymer)
[Glass transition tempreture]	~118 °C
[Beta transition tempreture]	~60 °C
Boiling point	200.0 °C
Refractive index	1.492 (λ=589.3 nm)
V-number	55.3
SMILES	C[C](C)C(=O)OC

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).

Properties

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.

Grades

§                     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)

Uses

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.

Acrylonitrile Butadine Styrene

Acrylonitrile butadiene styrene, or ABS, (chemical formula (C₈H₈· C₄H₆·C₃H₃N)_x) is a common thermoplastic used to make light, rigid, molded products such as pipes, golf club heads (used for its good shock absorbance), automotive body parts, wheel covers, enclosures, protective head gear, and toys including LEGO bricks. It is a copolymer made by polymerizing styrene and acrylonitrile in the presence of polybutadiene. The proportions can vary from 15% to 35% acrylonitrile, 5% to 30% butadiene and 40% to 60% styrene. The result is a long chain of polybutadiene criss-crossed with shorter chains of poly(styrene-co-acrylonitrile). The nitrile groups from neighbouring chains, being polar, attract each other and bind the chains together, making ABS stronger than pure polystyrene. The styrene gives the plastic a shiny, impervious surface. The butadiene, a rubbery substance, provides resilience even at low temperatures. ABS can be used between −25 °C and 60 °C.

Production of 1 kg of ABS requires the equivalent of about 2 kg of oil for raw materials and energy. It can also be recycled.

Synthesis

Acrylonitrile butadiene styrene can be found as a graft copolymer, in which styrene-acrylonitrile polymer is formed in a polymerization system in the presence of polybutadiene rubber latex; the final product is a complex mixture consisting of styrene-acrylonitrile copolymer, a graft polymer of styrene-acrylonitrile and polybutadiene and some unchanged polybutadiene rubber. There are, therefore, many variables to the process besides the different positions of the starting materials, so this technique is capable of producing polymers with a much wider range of properties. [Brighton et al. 1979] ABS can be made by blending, the technique involved mechanical blending by mixing a butadiene-acrylonitrile rubber with styrene-acrylonitrile resins, the process is being carried out under such conditions that the two polymers underwent some grafting. This technique is rather limited and has been largely suppressed by chemical process. [Brighton et al. 1979]

Properties

ABS is derived from acrylonitrile, butadiene, and styrene. Where acrylonitrile are synthetic monomers produced from propylene and ammonia; butadiene is a petroleum hydrocarbon obtained from butane; and styrene monomers, derived from coal, are commercially obtained from benzene and ethylene from coal. The advantage of ABS is that this material combines the strength and rigidity of the acrylonitrile and styrene polymers with the toughness of the polybutadiene rubber. The most amazing mechanical properties of ABS are resistance and toughness. A variety of modifications can be made to improve impact resistance, toughness, and heat resistance. For instance, the impact resistance can be amplified by increasing the proportions of polybutadiene in relation to styrene and acrylonitrile although this causes changes in other properties. Impact resistance does not fall off rapidly at lower temperatures. Stability under load is excellent with limited loads. Even though ABS plastics are used largely for mechanical purposes, they also have good electrical properties that are fairly constant over a wide range of frequencies. These properties are little affected by temperature and atmospheric humidity in the acceptable operating range of temperatures. [Harper, 1975] The final properties will be influenced to some extent by the conditions under which the material is processed to the final product; for example, molding at a high temperature improves the gloss and heat resistance of the product whereas the highest impact resistance and strength are obtained by molding at low temperature. ABS polymers are resistant to aqueous acids, alkalis, concentrated hydrochloric and phosphoric acids, alcohols and animal, vegetable and mineral oils, but they are swollen by glacial acetic acid, carbon tetrachloride and aromatic hydrocarbons and are attacked by concentrated sulfuric and nitric acids. They are soluble in esters, ketones and ethylene dichloride. The aging characteristics of the polymers are largely influenced by the polybutadiene content, and it is normal to include antioxidants in the composition. [Brighton et al. 1979] On the other hand, the cost of producing ABS is roughly twice the cost of producing polystyrene, ABS is considered superior for its hardness, gloss, toughness, and electrical insulation properties. However, it will be degraded when exposed to acetone.

Trivia

§                     Acrylonitrile butadiene styrene is the plastic from which Lego bricks are made.

Thermosetting polymer

A thermosetting plastic, also known as a thermoset, is polymer material that irreversibly cures. The cure may be done through heat (generally above 200 °C (392 °F)), through a chemical reaction (two-part epoxy, for example), or irradiation such as electron beam processing.

Thermoset materials are usually liquid or malleable prior to curing and designed to be molded into their final form, or used as adhesives. Others are solids like that of the molding compound used in semiconductors and integrated circuit (IC). Once hardened a thermoset resin cannot be reheated and melted back to a liquid form.

According to IUPAC recommendation: A thermosetting polymer is a prepolymer in a soft solid or viscous state that changes irreversibly into an infusible, insoluble polymer network by curing. Curing can be induced by the action of heat or suitable radiation, or both. A cured thermosetting polymer is called a thermoset.

Process

The curing process transforms the resin into a plastic or rubber by a crosslinking process. Energy and/or catalysts are added that cause the molecular chains to react at chemically active sites (unsaturated or epoxy sites, for example), linking into a rigid, 3-D structure. The cross-linking process forms a molecule with a larger molecular weight, resulting in a material with a higher melting point. During the reaction, the molecular weight has increased to a point so that the melting point is higher than the surrounding ambient temperature, the material forms into a solid material.

Uncontrolled reheating of the material results in reaching the decomposition temperature before the melting point is obtained. Therefore, a thermoset material cannot be melted and re-shaped after it is cured. This implies that thermosets cannot be recycled, except as filler material.

Properties

Thermoset materials are generally stronger than thermoplastic materials due to this three dimensional network of bonds (cross-linking), and are also better suited to high-temperature applications up to the decomposition temperature. However, they are more brittle. Many thermosetting polymers are difficult to recycle.

Examples

Some examples of thermosets are given below:

§                    Polyester fibreglass systems: sheet molding compounds and bulk molding compounds)

§                    Vulcanized rubber

§                    Duroplast, light but strong material, similar to bakelite used for making car parts

§                    Urea-formaldehyde foam used in plywood, particleboard and medium-density fiberboard

§                    Melamine resin used on worktop surfaces

§                    Epoxy resin used as the matrix component in many fiber reinforced plastics such as glass reinforced plastic and graphite-reinforced plastic)

§                    Polyimides used in printed circuit boards and in body parts of modern airplanes

§                    Cyanate esters or polycyanurates for electronics applications with high demands on dielectric properties and high glass temperature requirements in composites

§                    Mold or mold runners (the black plastic part in integrated circuits or semiconductors)

Some methods of molding thermosets are:

§                    Reactive injection molding (used for objects such as milk bottle crates)

§                    Extrusion molding (used for making pipes, threads of fabric and insulation for electrical cables)

§                    Compression molding (used to shape most thermosetting plastics)

§                    Spin casting (used for producing fishing lures and jigs, gaming miniatures, figurines, emblems as well as production and replacement parts)

MATERIALS                                                                                                                                            

Thermosets

          Natural Rubber

• Bakelite, a Phenol Formaldehyde Resin (used in electrical insulators and plastic wear)

• Duroplast

• Urea-Formaldehyde Foam (used in plywood, particleboard and medium-density fibreboard)

• Melamine (used on worktop surfaces)

• Polyester Resin (used in glass-reinforced plastics/Fibreglass (GRP)

• Epoxy Resin