Poly(methyl methacrylate)

Description

Methyl methacrylate is one of the most common methacrylates. This acrylic monomer, the essential component of the fluid mixed to the powder, may cause allergic contact dermatitis mainly in dental technicians and dentists. Cases were also reported in those using seulptured nails and in ceramics workers.

Chemical properties

white powder (or clear plastic sheet)

Chemical properties

Poly(methyl methacrylate) is a hard, rigid transparent substance. Straight poly(methyl methacrylate) is somewhat tougher than polystyrene but is less tough than the ABS polymers. An outstanding property of poly(methyl methacrylate) is its clarity. The material absorbs very little visible light but there is about 4% reflection at each polymer-air interface for normal incident light. Thus the transmission of normal incident light through a sheet of the polymer is about 92%. Poly(methyl methacrylate) is a polar material and has a rather high dielectric constant and power factor; it is a good electrical insulator at low frequencies but is less satisfactory at high frequencies.
Poly(methyl methacrylate) prepared by free radical polymerization is amorphous and is therefore soluble in solvents of similar solubility parameter. Effective solvents include aromatic hydrocarbons such as benzene and toluene; chlorinated hydrocarbons such as chloroform and ethylene dichloride; and esters such as ethyl acetate and amyl acetate. Some organic materials, although not solvents for the polymer, cause crazing and cracking, e.g. aliphatic alcohols and amines. Poly(methyl methacrylate) has very good resistance to attack by water, alkalis, aqueous inorganic salts and most dilute acids. Some dilute acids such as hydrocyanic and hydrofluoric acids, however, do attack the polymer, as do concentrated oxidizing acids. Poly(methyl methacrylate) has much better resistance to hydrolysis than poly(methyl acrylate), probably by virtue of the shielding presented by the a-methyl group. Poly(methyl methacrylate) may be converted to poly(sodium methacrylate) only by rather drastic treatment with, for example, molten sodium hydroxide.
A further outstanding property of poly(methyl methacrylate) is its good outdoor weathering, in which respect the material is markedly superior to most other thermoplastics. After several years under tropical conditions the colour change is extremely small. When poly(methyl methacrylate) is heated above the glass transition temperature (105°C) it becomes rubbery and sheet material is easily manipulated at 150-160°C. Above about 200°C decomposition becomes appreciable and at 350-450°C a nearly quantitative yield of monomer is readily obtained. Thus the recovery of monomer from scrap polymer is a feasible proposition.

The Uses of Poly(methyl methacrylate)

Poly(methyl methacrylate) is used in production of Carbonate-olefin based copolymer for molded plastics.

The Uses of Poly(methyl methacrylate)

Poly(methyl methacrylate) may be used as a reference suspension polymer for the analysis of the composition of poly(methyl methacrylate) (PMMA) by gas chromatography method.

The Uses of Poly(methyl methacrylate)

PMMA/HA (Hydroxyapatite) composites have be used in biomedical applications such as dentistry, orthopedic retainers, and bone replacement. It has been used as substrate for graphene growth.
Some studies report its use as
PMMA-titania hybrid optical thins films
PMMA/polystryrene/clay nanocomposites
PMMA/polyurethane/carbon black nanocomposites for methanol fuel cells.

Definition

ChEBI: A macromolecule composed of repeating methyl methacrylate units.

Preparation

The polymerization of methyl methacrylate:

is readily accomplished by bulk, solution, suspension and emulsion techniques. Of these methods, bulk and suspension polymerization are mainly used for the production of the homopolymer.
(a) Bulk polymerization
Techniques which involve a combination of bulk polymerization and casting are extensively used in the manufacture of poly(methyl methacrylate) sheet. In most processes, the first step is the preparation of a partially polymerized material. Typically, monomer is stirred with benzoyl peroxide (0.5%) at 90??C for about 10 minutes to give a syrup which is then cooled to room temperature. Colourant, plasticizer and ultraviolet absorber, if required, are added at this point. At this stage the degree of conversion of monomer to polymer is about 20%; the use of such a syrup reduces shrinkage in the casting cell and also lessens leakage from the cell. The syrup is then poured into a casting cell, consisting of two glass plates separated by a rubber gasket. The plates are held together by spring-loaded clamps so that the plates continuously move together in response to the shrinkage of approximately 20% which occurs on conversion of monomer to polymer. The filled cell is then passed through a heating tunnel wherein the temperature is maintained at 40??C for 15 hours and then 95??C for 1 hour. The sheet is then cooled and removed from the cell. With castings of thickness greater than about 2 cm, the exothermic reaction may result in local temperatures above the boiling point of the monomer (100Se) and bubbles may form. In such cases, polymerization may be carried out under pressure so that the boiling point of the monomer is raised.
Rod is also manufactured by casting. In one process, syrup is contained in vertical aluminium tubes which are very slowly lowered into a bath at 40??C. As the lowest portion of syrup polymerizes it contracts and the syrup above moves downwards. In this way a homogeneous rod, free from voids, is obtained. Dentures are normally made from a polymer-monomer dough in a plaster mould. Bulk polymerization carried out in the preparation of sheet, as described above, results in polymer of very high average molecular weight (??10⁶).
(b) Suspension polymerizution
Suspension polymerization of methyl methacrylate is used mainly for the production of injection moulding and extrusion grades of polymer. Suspension polymer is also used in the preparation of polymer-monomer doughs for dentures. Polymerization is carried out batch-wise in a stirred reactor, jacketed for heating and cooling; the reactor is capable of withstanding a pressure of 0.3--0.4 MPa (3-4 atmospheres).
Reaction is carried out under nitrogen. Typically, the mixture is initially heated to about 80??C but the exothermic reaction causes the temperature to rise to about 120??C, with accompanying increase in pressure. Polymerization is rapid and is complete in about 1 hour. The suspension is cooled and acidified with sulphuric acid to remove the suspending agent. The beads of polymer are then filtered off, washed and dried in air at about 80??C. The dried beads may be used for moulding without further treatment or they may be compounded with additives (e.g. colourants), extruded and granulated.
Suspension polymerized poly(methyl methacrylate) normally has an average molecular weight of about 60000.

General Description

Poly (methyl methacrylate) (PMMA) is an amorphous transparent thermoplastic polymer. PMMA is recognized as an optical polymer based on its refractive index of 1.49. Hence, it is used in optical fibers.It finds uses in biological applications because of its low water absorption capability and biocompatible.The maximum moisture content of PMMA is 1.71% and SBF absorption is 1.96%.Simulated Body fluid test (SBF) is a method to characterize the in vitro bioactivity of ceramic materials, by immersing the materials in an aqueous SBF solution.

Safety Profile

Questionable carcinogen with experimental tumorigenic data by implant route. When heated to decomposition it emits acrid smoke and irritating fumes. Used as the main constituent of acrylic sheet, moldmg, and extrusion powders.