Published on: Mar 4, 2016
Transcripts - Poly(phenylethene) (polystyrene)
Poly(phenylethene), commonly known as polystyrene, is the third most important
polymer, in terms of amount made from ethene. Its physical properties can be
adjusted to suit a range of everyday uses. Techniques have been developed which
increase its mechanical strength, its ability to absorb shock and its thermal
Polymers Poly(phenylethene) (Polystyrene)
Uses of poly(phenylethene) (polystyrene)
The largest use for poly(phenylethene) is for packaging, particularly for foods such as poultry and eggs, for cold
drinks and take-away meals.
Figure 1 Uses of poly(phenylethene).
It is also used in making appliances, including refrigerators, microwaves and blenders. It is the leading choice for
jewel boxes (cases for CDs and DVDs) and is also widely used for its insulating properties.
Annual production of poly(phenylethene) (polystyrene)
World 14.6 million tonnes
Europe 3.4 million tonnes
US 4.0 million tonnes1
Russia 0.27 million tonnes2
1. American Chemistry Council 2013 Statistics
2. Federal State Statistics: Russian Federation 2011
Manufacture of poly(phenylethene) (polystyrene)
Poly(phenylethene) is manufactured from its monomer, phenylethene. Phenylethene, in turn, is produced from
benzene and ethene via ethylbenzene. There are thus three stages:
a) the manufacture of ethylbenzene from benzene
b) the manufacture of phenylethene (styrene)
c) the polymerization of phenylethene (styrene)
(a) The manufacture of ethylbenzene from benzene
Benzene vapour and ethene are mixed and passed over an acid catalyst, at 650 K and 20 atm pressure:
Materials and applications
Polymers: an overview
Figure 2 This
has a fairing (the
structure around the
bike that reduces
drag by streamlining)
made of a blend of
ABS and a polyamide.
It is light, very strong
and has a high
chemical and heat
This is an example of a Friedel-Crafts reaction. The acid catalyst now used is a zeolite, ZSM-5, an
(b) The manufacture of phenylethene (styrene)
Ethylbenzene vapour is mixed with excess steam and passed over heated iron(lll) oxide. Other metal oxides used
as the catalyst including those of magnesium, chromium(III) and zinc, usually coated on carbon or alumina. It is
A small amount of potassium oxide is mixed with the iron(lll) oxide (which keeps the catalyst in the iron(lll) state).
The steam reduces 'coking' (the formation of soot on the catalyst from the decomposition of ethylbenzene at the
high temperatures used).
(c) The polymerization of phenylethene (styrene)
Radical polymerization is used to produce the polymer. The process is an example of addition polymerization
The predominant polymerization technique is continual thermal mass polymerization which is initiated by heat
alone. Suspension polymerization is also used. This technique requires the use of an initiator such as dibenzoyl
Poly(phenylethene) is a clear thermoplastic, with good moisture resistance, but is rather brittle. A tougher
product is also manufactured by polymerizing phenylethene containing 5-10% dissolved poly(buta-1,3-diene)
rubber. This tougher product - generally knownas High Impact Polystyrene (HIPS) - is made exclusively by
continuous thermal mass polymerization, in which heat is required to initiate the polymerization reaction. This
toughened polymer is translucent.
The structure of poly(phenylethene) made by these technologies is completely random in structure and is known
as an atactic structure. By modification of the polymerization technique - principally by the use of metallocene
catalysts - stereoregular (syndiotactic) structures can be obtained. This syndiotactic polymer (sPS) has
improved properties - particularly thermal and mechanical.
Another co-polymer is formed on polymerizing a mixture of phenylethene (styrene) and propenonitrile
(acrylonitrile). It is known as SAN (styrene-acrylonitrile). It is less flexible, more transparent and has more
resistance to heat and chemicals than poly(phenylethene). It is used in car headlamps, cassette covers, syringes
and high quality kitchen appliances.
A further modification involves the co-polymerization of phenylethene (styrene) with propenonitrile (acrylonitrile)
in the presence of poly(buta-1,3-diene) to make ABS plastics. A, B, S represent acrylonitrile, butadiene and
styrene, which give strength (A), flexibility (B), and hardness (S). Typically this plastic has a composition: 60%
(w/w) phenylethene (styrene), 25% propenonitrile (acrylonitrile), 15% buta-1,3-diene. The initiator used is often
potassium peroxydisulfate, K2S2O8.
means the fairing can
be installed near the
engine and the
By kind permission of
Figure 3 These
beads are shown prior to
and after expansion.
They were impregnated
during manufacture with
very fine particles of
graphite to improve
further their ability to
By kind permission of
ABS is tougher, scratch proof and more chemically resistant than rubber-modified poly(phenylethene) and is
used, for example, in casings for computers, cycle helmets, calculators, telephones, vacuum cleaners and toys.
Often ABS is blended with SAN to make it even more rigid.
Another variation is the co-polymer formed between ABS and methyl 2-methylpropenoate, which has a high
resistance to chemical attack, high transparency and is very tough.
Expanded poly(phenylethene) (polystyrene)
Expanded poly(phenylethene) is manufactured as beads containing pentane (a liquid at room temperature).
When they are heated in steam, the hydrocarbon volatilises and the beads expand (Figure 3). These are
subsequently blown into moulds and fused by further steaming and then cooling. The expanded
poly(phenylethene) has good thermal insulation and shock absorbing properties.
Date last amended: 2nd January 2014
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