Poly(methyl 2-methylpropenoate), often known as polymethyl methacrylateor PMMA, is one of the best known polymers, used widely under trade namessuch as Lucite, Perspex and Altuglas.

Polymers Poly(methyl 2-methylpropenoate) (Polymethyl methacrylate)

Poly(methyl 2-methylpropenoate)

Uses of poly(methyl 2-methylpropenoate) (polymethyl methacrylate)Poly(methyl 2-methylpropenoate) is better known as Lucite, Perspex and Altuglas (when in sheet form)and as Diakon (when in powder form).

The cast sheet is used in baths and other sanitary ware, which along with illuminated signs, is the largestuse of the polymer. High molecular mass cast sheet (Perspex) is also used as a lightweight replacementfor glass. Lower molecular mass products, made by suspension or solution polymerization (Diakon), areused in car lights and domestic lighting.

Special grades are used in diverse applications such as false teeth and eyes and as a major componentof bone cements.

The monomer is used in adhesives, surface coatings and in paints.

Figure 1 Uses of poly(methyl-2-methylpropenoate).

Annual production of poly(methyl 2-methylpropenoate) (polymethylmethacrylate)Polymer

World 1.6 million tonnes

Europe 490 000 tonnes

CONTENTS

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Introduction

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Polymers

Polymers: an overview

Degradable plastics

Methanal plastics

(Formaldehyde plastics)

Polyamides

Polycarbonates

Poly(chloroethene)

(Polyvinyl chloride)

Polyesters

Poly(ethene)

(Polyethylene)

Poly(methyl 2-

methylpropenoate)

(Polymethyl methacrylate)

Poly(phenylethene)

(Polystyrene)

Poly(propene)

(Polypropylene)

Poly(propenoic acid)

(Polyacrylic acid)

Poly(propenonitrile)

(Polyacrylonitrile)

Poly(tetrafluoroethene)

(Polytetrafluoroethylene)

Polyurethanes

Silicones

Metals

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MonomerWorld 3.6 million tonnes

Europe 800 000 tonnes

China 410 000 tonnes

Rest of Asia 1.4 million tonnes

Manufacture of poly(methyl 2-methylpropenoate) (polymethylmethacrylate)(a) The monomerThe monomer is the methyl ester of 2-methylpropenoic acid, methyl 2-methylpropenoate (methylmethacrylate):

Currently, most of the monomer is made by two processes

(i) From propanone (acetone)Worldwide, over 80% of the monomer is made from propanone by a sequence of steps which begins byreacting propanone with hydrogen cyanide.

Figure 2 The hydrogen cyanide ismanufactured from ammonia andmethane. A mixture of thegaseous reactants is passedthrough a platinum-rhodiumgauze catalyst. The heatgenerated by the reaction keepsthe gauze glowing red at 1270 K. The photograph was takenthrough a sight glass located onthe reactor.

Propanone and hydrogen cyanide form 2-hydroxy-2-methylpropanonitrile:

This product, on reaction with concentrated sulfuric acid at about 430 K, is dehydrated and the nitrilegoup (CN) hydrolyzed to the amide. This is a step-wise process involving both dehydration andhydrolysis. The reactions can be summarised as:

The temperature is decreased to 370 K and methanol is added. The amide group is hydrolyzed andesterified. The reactions can be summarised as:

The product is continuously removed by steam distillation.A drawback to the process is the co-production of ammonium sulfate. Together with 'spent' sulfuric acidfrom the reactions above, the ammonium salt is heated strongly in oxygen in a furnace, in a processsimilar to that used for recycling sulfuric acid. The products formed are nitrogen, carbon dioxide andsulfur dioxide. The latter is then converted to sulfuric acid using the Contact Process. The use of pureoxygen reduces the size of the furnace which saves on both energy and equipment costs.

(ii) From ethene, carbon monoxide and methanolMuch work has been done to find alternative sources of the monomer and a promising route, which isnow in use, uses a mixture of ethene, carbon monoxide and methanol in the liquid phase under pressureof about 10 atm at 350 K:

The resulting ester, methyl propionate, is reacted with methanal to form methyl 2-methylpropenoate. Afixed bed reactor is used and the reactor and catalyst (for example, caesium hydroxide on silica) areheated to 600 K:

Figure 3 The building of the first site for the manufacture of methyl 2-methylpropenoate, the monomer usedto make poly(methyl 2-methylpropenoate), from ethene, carbon monoxide and methanol. The site is onJurong Island just off the shore of Singapore.1 The reactor to make methyl propanoate from ethene, carbon monoxide and methanol. 2 The reactor to make methyl 2-methylpropenoate frpm methyl propanoate and methanal.3 Storage vessels.4 Section being built for drying methanal, produced in aqueous solution from methanol.5 Section being built to handle waste gases.6 Drying column ready for installation at 4.

7 Control room for the site.8 E;ectrical switch room.9 Section being built for the purification of methyl 2-methylpropenoate.

(b) The polymerPolymerization of methyl 2-methylpropenoate is achieved by a free radical process using an initiator,such as an azo compound or a peroxide:

The amount of initiator employed affects both polymerization rate and resulting molecular mass of thepolymer. Polymerization is carried out commercially in several ways, i.e. in bulk, solution, suspension andemulsion.

The process is an example of addition polymerization.

(c) Co-polymersCo-monomers are often used together with the methyl 2-methylpropenoate. For example, mostcommercial grades of poly(methyl 2-methylpropenoate) used in injection moulding or extrusionapplications contain a small amount (ca. 4%) of co-monomer, such as methyl propenoate (methylacrylate) (when casting sheets of the polymer) and ethyl propenoate (ethyl acrylate) (when extrudingsheets of the polymer).

In these co-polymers, the monomers are randomly arranged. The resulting polymers have increasedthermal stability compared to the homopolymer.

With butyl propenoate (butyl acrylate), a co-polymer is produced which is used as a base for emulsionpaints.

It is also co-polymerized with ABS to produce a very tough polymer which is both rigid and has excellentclarity. It is used, for example, in medical applications and in cosmetic packaging.

Date last amended: 3rd October 2013

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