Methyl methacrylate

Description

Methyl methacrylate is an organic compound with the formula CH₂=C(CH₃)COOCH₃. This colourless liquid, the methyl ester of methacrylic acid (MAA) is a monomer produced on a large scale for the production of poly(methyl methacrylate) (PMMA).

Chemical Properties

Methyl methacrylate is a methyl ester of methacrylic acid. It is a colourless, volatile liquid with an acrid fruity odour. It has a relatively high vapour pressure (4 kPa at 20°C), moderate water solubility (15.8 g/litre), and a low log octanol/water partition coefficient (Kow = 1.38) . Methyl methacrylate is typically 99.9% pure and contains small amounts of inhibitor to retard polymerization.

Physical properties

Clear, colorless liquid with a penetrating, fruity odor. An experimentally determined odor threshold concentration of 210 ppb_v was reported by Leonardos et al. (1969). Experimentally determined detection and recognition odor threshold concentrations were 200 μg/m³ (49 ppb_v) and 1.4 mg/m³ (340 ppb_v), respectively (Hellman and Small, 1974).

Uses

The principal application, consuming approximately 80% of the MMA, is the manufacture of poly methyl methacrylate acrylic plastics (PMMA). Methyl methacrylate is also used for the production of the co-polymer methyl methacrylate-butadiene-styrene (MBS), used as a modifier for PVC. Another application is as cement used in total hip replacements as well as total knee replacements. Used as the "grout" by orthopedic surgeons to make the bone inserts fix into bone, it greatly reduces post-operative pain from the insertions but has a finite lifespan. Typically the lifespan of methyl methacrylate as bone cement is 20 years before revision surgery is required. Cemented implants are usually only done in elderly populations that require more immediate short term replacements. In younger populations, cementless implants are used because their lifespan is considerably longer. Also used in fracture repair in small exotic animal species using internal fixation.

Preparation

Prepared by the esterification of methacrylamide sulfate with methanol.

Production Methods

The compound is manufactured by several methods, the principal one being the acetone cyanohydrin (ACH) route, using acetone and hydrogen cyanide as raw materials. The intermediate cyanohydrin is converted with sulfuric acid to a sulfate ester of the methacrylamide, methanolysis of which gives ammonium bisulfate and MMA. Although widely used, the ACH route coproduces substantial amounts of ammonium sulfate. Some producers start with an isobutylene or, equivalently, tert-butanol, which is sequentially oxidized first to methacrolein and then to methacrylic acid, which is then esterified with methanol. Propene can be carbonylated in the presence of acids to iso butyric acid, which undergoes subsequent dehydrogenation . The combined technologies afford more than 3 billion kilograms per year. MMA can also be prepared from methyl propionate and formaldehyde.

Definition

ChEBI: Methyl methacrylate is an enoate ester having methacrylic acid as the carboxylic acid component and methanol as the alcohol component. It has a role as an allergen and a polymerisation monomer. It is an enoate ester and a methyl ester. It is functionally related to a methacrylic acid.

General Description

A clear colorless liquid. Slightly soluble in water and floats on water. Vapors heavier than air. Vapors irritate the eyes and respiratory system. Containers must be heavily insulated or shipped under refrigeration. An inhibitor such as hydroquinone, hydroquinone methyl ester and dimethyl t-butylphenol is added to keep the chemical from initiating polymerization. The chemical may polymerize exothermically if heated or contaminated with strong acid or base. If the polymerization takes place inside a container, the container may rupture violently. Used to make plastics.

Air & Water Reactions

Highly flammable. Very slightly soluble in water.

Reactivity Profile

Methyl methacrylate, may polymerize if contaminated or subjected to heat. If polymerization takes place in a container, the container is subject to violent rupture. Oxidizes readily in air to form unstable peroxides that may explode spontaneously [Bretherick 1979. p.151-154, 164]. Peroxides may also initiate exothermic polymierization of the bulk material [Bretherick 1979. p. 160]. Benzoyl peroxide was weighed into a beaker that had previously been rinsed with methyl methacrylate. The peroxide catalyzed polymerization of the methyl methacrylate and the build-up of heat ignited the remaining peroxide [MCA Case History 996. 1964].

Hazard

Flammable, dangerous fire risk, explosivelimits in air 2.1–12.5%. Eye and upper respiratorytract irritant, body weight effects, and pulmonaryedema. Questionable carcinogen.

Health Hazard

1. Methyl methacrylate may cause slight eye irritation or moderate skin irritation. It is considered a skin sensitizer; allergic reactions may result from contact. Inhalation of vapor or mist can cause irritation of the nose, throat, and lungs and can be fatal in high concentrations. Prolonged or repeated overexposure has been reported to affect the kidneys, liver, gastrointestinal tract, nervous system and lung.
2. Methyl methacrylate is moderately toxic to aquatic organisms on an acute basis. The bioconcentration potential (tendency to accumulate in the food chain) is low. If released to surface water, methyl methacrylate will readily biodegrade. A portion may evaporate to the air. It will not persist in the environment.
3. Irritation of eyes, nose, and throat. Nausea and vomiting. Liquid may cause skin irritation.

Fire Hazard

Behavior in Fire: Vapor is heavier than air and may travel a considerable distance to a source of ignition and flash back. Containers may explode in fire or when heated because of polymerization.

Industrial uses

Initiators for methyl methacrylate polymerization include AIBN, dilauroyl peroxide (LPO), and 2,2'-Azobis[2-(2-imidazolin-2- yl)propane].

Safety Profile

Moderately toxic by inhalation and intraperitoneal routes. Mildly toxic by ingestion. Human systemic effects by inhalation: sleep effects, excitement, anorexia, and blood pressure decrease. Experimental teratogenic and reproductive effects. Mutation data reported. A skin and eye irritant. Questionable carcinogen with experimental tumorigenic data. A common air contaminant. A very dangerous fire hazard when exposed to heat or flame; can react with oxidizing materials. Explosive in the form of vapor when exposed to heat or flame. The monomer may undergo spontaneous, explosive polymerization. Reacts in air to form a heat-sensitive explosive product (explodes on evaporation at 6OOC). May ignite on contact with benzoyl peroxide. Potentially violent reaction with the polymerization initiators azoisobutyronitrile, dibenzoyl peroxide, di-tert-butyl peroxide, propionaldehyde. To fight fire, use foam, CO2, dry chemical. When heated to decomposition it emits acrid smoke and irritating fumes.

Potential Exposure

Virtually all of the methyl methacrylate monomer produced is used in the production of polymers, such as surface coating resins; plastics (Plexiglas and Lucite); ion exchange resins; and plastic dentures.

Carcinogenicity

In several lifetime animal studies, there was no evidence that methyl methacrylate is carcinogenic.

Environmental Fate

Chemical/Physical. Polymerizes easily (Windholz et al., 1983). Methyl methacrylate undergoes nucleophilic attack by OH ions in water (hydrolysis) resulting in the formation of methacrylic acid and methanol (Kollig, 1993). Hydrolysis occurs at a rate of 171/M?h at 25 °C (Sharma and Sharma, 1970). No measurable hydrolysis was observed at 85.0 °C (pH 7) and 25 °C (pH 7.07). Hydrolysis half-lives of 9 and 134 min were observed at 66.0 °C (pH 9.86) and 25.0 °C (pH 11.3), respectively (Ellington et al., 1987).

storage

Methyl methacrylate is a reactive chemical that must be stored and handled with care. It is stable under recommended storage conditions. Heat can cause polymerization. Inhibitor is added to methyl methacrylate monomer to prevent polymerization. For the inhibitor to be effective, the oxygen concentration in the vapor space must be at least 5%. Store material in containers made of stainless steel, carbon steel, glass, or aluminum. Avoid contact with acids, bases, oxidizing agents, reducing agents, UV light (ultraviolet light, which is found in sunlight), free-radical initiators, and organic peroxides.

Shipping

UN1247 Methyl methacrylate monomer, stabilized, Hazard Class: 3; Labels: 3-Flammable liquid.

Purification Methods

Wash the ester twice with aqueous 5% NaOH (to remove inhibitors such as hydroquinone) and twice with water. Dry it with CaCl2, Na2CO3, Na2SO4 or MgSO4, then with CaH2 under nitrogen under reduced pressure. The distillate is stored at low temperatures and redistilled before use. Prior to distilling, inhibitors such as hydroquinone (0,004%), .-naphthylamine (0.2%) or di--naphthol are sometimes added. Also purify it by boiling with aqueous H3PO4 solution and finally with saturated NaCl solution. It is dried for 24hours over anhydrous CaSO4, distilled at 0.1mm Hg at room temperature and stored at -30o [Albeck et al. J Chem Soc, Faraday Trans 1 1 1488 1978]. [Beilstein 2 II 398, 2 III 1279, 2 IV 1519.]

Incompatibilities

Vapor may form explosive mixture with air. Reacts in air to form a heat-sensitive explosive product @ 60C. Incompatible with nitrates, oxidizers, peroxides, strong acids; strong alkalis; oxidizers, reducing agents; amines, moisture. Contact with benzoyl peroxide may cause ignition, fire and explosion. May polymerize if subjected to heat, polymerization catalysts e. g., azoisobutyronitrile, dibenzoyl peroxide; di-tert-butyl peroxide, propionaldehyde); strong oxidizers; or ultraviolet light. May contain an inhibitor, such as hydroquinone.

Waste Disposal

Consult with environmental regulatory agencies for guidance on acceptable disposal practices. Generators of waste containing this contaminant (≥100 kg/mo) must conform to EPA regulations governing storage, transportation, treatment, and waste disposal. Incineration may be allowed.