Poly(methyl 2-methylpropenoate), also known as polymethyl methacrylate (PMMA), is a clear plastic that is used in various applications like sanitary ware, signs, replacement glass, and car lights. It is produced from methyl methacrylate monomer, which is mainly made from propanone and hydrogen cyanide or from ethene, carbon monoxide, and methanol. The polymer is made through free radical polymerization of the monomer, which can be done in bulk, solution, suspension or emulsion. Co-polymers are also used for properties like increased thermal stability.
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Poly(methyl 2 methylpropenoate)
1. Poly(methyl 2-methylpropenoate), often known as polymethyl methacrylate
or PMMA, is one of the best known polymers, used widely under trade names
such 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 largest
use of the polymer. High molecular mass cast sheet (Perspex) is also used as a lightweight replacement
for glass. Lower molecular mass products, made by suspension or solution polymerization (Diakon), are
used in car lights and domestic lighting.
Special grades are used in diverse applications such as false teeth and eyes and as a major component
of 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) (polymethyl
methacrylate)
Polymer
World 1.6 million tonnes
Europe 490 000 tonnes
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Poly(methyl 2-
methylpropenoate)
(Polymethyl methacrylate)
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(Polystyrene)
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(Polypropylene)
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(Polyacrylic acid)
Poly(propenonitrile)
(Polyacrylonitrile)
Poly(tetrafluoroethene)
(Polytetrafluoroethylene)
Polyurethanes
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2. Monomer
World 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) (polymethyl
methacrylate)
(a) The monomer
The monomer is the methyl ester of 2-methylpropenoic acid, methyl 2-methylpropenoate (methyl
methacrylate):
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 by
reacting propanone with hydrogen cyanide.
Figure 2 The hydrogen cyanide is
manufactured from ammonia and
methane. A mixture of the
gaseous reactants is passed
through a platinum-rhodium
gauze catalyst. The heat
generated by the reaction keeps
the gauze glowing red at 1270 K.
The photograph was taken
through a sight glass located on
the reactor.
3. 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 nitrile
goup (CN) hydrolyzed to the amide. This is a step-wise process involving both dehydration and
hydrolysis. The reactions can be summarised as:
The temperature is decreased to 370 K and methanol is added. The amide group is hydrolyzed and
esterified. 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 acid
from the reactions above, the ammonium salt is heated strongly in oxygen in a furnace, in a process
similar to that used for recycling sulfuric acid. The products formed are nitrogen, carbon dioxide and
sulfur dioxide. The latter is then converted to sulfuric acid using the Contact Process. The use of pure
oxygen reduces the size of the furnace which saves on both energy and equipment costs.
(ii) From ethene, carbon monoxide and methanol
Much work has been done to find alternative sources of the monomer and a promising route, which is
now in use, uses a mixture of ethene, carbon monoxide and methanol in the liquid phase under pressure
of about 10 atm at 350 K:
The resulting ester, methyl propionate, is reacted with methanal to form methyl 2-methylpropenoate. A
fixed bed reactor is used and the reactor and catalyst (for example, caesium hydroxide on silica) are
heated to 600 K:
4. Figure 3 The building of the first site for the manufacture of methyl 2-methylpropenoate, the monomer used
to make poly(methyl 2-methylpropenoate), from ethene, carbon monoxide and methanol. The site is on
Jurong 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.