This note contains synthesis of important monomers from hydrocarbons and prooduction of associated polymers which are most frequently used for textiles.

1. MANUFACTURING OF IMPORTANT POLYMERS AND POLYMER
PROCESSING
Bademaw Abate (Msc, Lecturer)
SYNTHESIS OF POLYAMIDES
PRODUCTION OF NYLON 6.6 POLYMER
Reactant Synthesis
Nylon 6.6 polymer is made by condensation of two substances: (a) adipic acid, and (b)
hexamethylene diamine.
These starting materials are synthesized usually via one or other of three routes.
(1) Cyclohexanol Route
This is the original route used in making the starting materials for nylon 6.6, and it is still the
route by which much of the nylon 6.6 is made today. The stages in the synthesis are shown
below. Originally, cyclohexanol was made from phenol, which was, in turn, obtained from the
benzene distilled from coal tar or petroleum. The phenol is reduced to cyclohexanol by
hydrogenation in the presence of a catalyst (1). Much of the cyclohexanol used today is produced
by a more direct route from benzene, which is reduced to cyclohexane (2); the latter is then
oxidized by air in the presence of catalyst, forming a mixture of cyclohexanol and
cyclohexanone (3).
Cyclohexanol, or the mixture of cyclohexanol and cyclohexa-none produced by the second route,
is oxidized to adipic acid(4). Hexamethylene diamine, the second starting material, is made from
adipic acid by the following route:
(a) Adipic acid is reacted with ammonia to form adipamide (5).
(b) Adipamide is dehydrated to adiponitrile (6).
(c) Adiponitrile is reduced to hexamethylene diamine withhydrogen in the presence of a
catalyst (7).

2. (2) Butadiene Route
Butadiene is a basic raw material of synthetic rubber manufac-ture in the U.S.A. and it is
produced in great quantity from petroleum. It is made into adiponitrile by the following route
(see below):
(a) Butadiene is chlorinated with chlorine gas, to form dichlorobutene(1).
(b) Dichlorobutene is treated with hydrocyanic acid, forming 1, 4-dicyanobutene (2).
(c) Dicyanobutene is hydrogenated in the presence of catalyst, to form adiponitrile (3).
Adiponitrile is then converted into adipic acid or hexamethy- lene diamine by hydrolysis or
reduction respectively.

3. POLYMERIZATION
The condensation reaction that results in the formation of nylon polymer takes place between
the amine groups on each end of the hexamethylene diamine, and the carboxyl groups on each
end of the adipic acid. If the two reactants are mixed in exact stoichiometric quantities, the
reaction could theoretically continue until all the small molecules had linked together into one
huge molecule. This could not, of course, take place in practice, as the opportunities for amine
end groups and carboxyl end groups to meet and react diminishes as polymerization proceeds,
and the mobility of the polymer molecules is reduced. If the two reactants are mixed together in
quantities which are not stoichiometrically balanced, the condensation reaction will proceed in
the normal way. But a point will be reached at which all the end groups of one type have been
reacted, and the end groups of the polymer chains are now all of the type present in the
component that was used in excess. The poly- merization will then stop.
The manner in which this imbalance of components affects polymerization is best illustrated by
considering an extreme case. If condensation is carried out, for example, using 1 molar pro-
portion of diacid to 2 molar proportions of diamine, the polymerization will result in the
production of a 'polymer' containing only three component residues, with amine groups on each
end of the molecule:
If the proportions of the two components are, say, 1 molar proportion of diacid to 1.25 molar
proportions of diamine, i.e.4 diacid molecules to 5 diamine molecules, then the polymer formed
would contain 9 component residues. The polymer molecule would again have amine groups at
each end, and further condensation would be impossible. Two important points are evident from
this effect of varying the balance of the components used in the polycondensation reaction;
a high degree of polymerization will be attained only by ensuring that the balance of
components is adequately controlled,
the degree of polymerization attained may be controlled by using components in carefully
calculated non-stoichiometric proportions, representing the required degree of imbalance.
Stabilization
In the production of nylon 6.6 polymer, it is necessary to allow the polymerization to proceed
until an adequate degree of polymerization has been attained. Polymers below a molecular
weight of about 5,000 will form fibres only with the greatest difficulty; polymers of molecular

4. weight between approximately 5,000 and 10,000 will form fibres which are generally too weak
for practical use. It is not until the molecular weight is greater than about 12,000 that fibres of
adequate strength are produced. It is necessary, therefore, that the polymerization conditions
should be such as to allow this degree of polymerization to be reached. As the degree of
polymerization increases still further, however, new difficulties arise. The polymer becomes
intransigent and difficult to melt and spin. In practice, it is necessary to control the
polymerization to provide a polymer of average molecular weight in the region of 12,000 to
22,000 the actual figure being determined by the fibre characteristics that are required. It is
apparent that the polymerization reaction can be con- trolled in this way by using extremely
highly purified components in very carefully calculated proportions. By suitable choice of the
balance of components, the polymerization may be stopped at any desired degree of
polymerization.
This technique is, in fact, used in practice. A common modification is to create the necessary
imbalance by using stoichiometric proportions of the two components, and adding a small
proportion of a monofunctional ingredient which serves as a chain growth stopper in the same
way as the extra proportion of a component. Acetic acid, for example, is added to the mixture of
hexamethylene diamine and adipic acid used in producing Nylon 6.6 polymer. The amount of
acetic acid is calculated to block the ends of the polymer chains after the desired average
molecular weight has been reached. This technique is called 'stabilization'.
Poly condensation
If the hexamethylene diamine and adipic acid are pure, they may be mixed in stoichiometric
quantities directly in aqueous solutions, the equivalence being determined by electrometric
titration. This solution is then used directly for the polymerization to nylon 6.6 polymer. The
correct stoichiometric balance between the two components may also be obtained by reacting the
two materials together to form a salt, hexamethylene diammonium adipate, in which one
molecule of each component is present. This is commonly called 'nylon salt'.
Nylon salt is prepared by neutralizing solutions of the two components in methanol. The salt is
relatively insoluble in methanol, and it crystallizes out as the solution cools. The crystals are
separated by centrifuging, washed and dried.

5. Nylon salt produced in this way is extremely pure. In it, the two nylon 6.6 components are
present in exact stoichiometric proportions. The salt is dissolved in water to form a 60 per cent
solution, and acetic or adipic acid is added in amount calculated to stop polymerization at the
desired stage. Condensation of the aqueous solution of nylon salt as carried out in a stainless
steel pressure vessel, using an inert atmosphere of nitrogen or hydrogen to ensure that oxygen is
excluded. Nylon polymer is extremely susceptible to decomposition in the presence of oxygen at
the temperatures used in condensation, and it is essential that all traces of oxygen should be kept
out of the vessel.
Condensation is commonly carried out in two stages:
(1) The solution is heated at 22O-230°C. for up to 2 hours, at a pressure of about 17.5 kg/cm2
(250 lb/in2).
(2) The temperature is raised gradually, and steam is allowed to escape from the vessel, the
pressure being at about 17.5 kg/cm2 (250 lb/in2). When the temperature has reached 275-280°C,
the molten material is held at this temperature at atmospheric pressure, or under vacuum, until
the desired degree of poly merization has been reached.
The molten polymer is then extruded through a slit in the base of the vessel, the ribbon of
viscous material falling on to a slow-moving wheel which is cooled by water. The polymer is
immediately chilled and solidifies to a tough ribbon of horn-like nylon 6.6 polymer
(polyhexamethylene adipamide), which is typically about 30 cm (12 in) wide and 6 mm (W in)
thick. The ribbon is passed into a machine which chops it into small pieces or chips.

6. NYLON 6-PRODUCTION
Reactant Synthesis
The caprolactam used in producing nylon 6 polymer is made by one of several routes, of which
the following are important:
(1) Cyclohexanone Route
This is the route by which caprolactam is commonly produced for nylon 6 manufacture.
Cyclohexanone may be made from benzene via one of several routes, including the following:

7. (a) Benzene is chlorinated to chlorobenzene (1), which is then converted to phenol (2). Phenol is
reduced to cyclohexanol (3), which is oxidized to cyclohexanone (4).
(b) Benzene is nitrated to nitrobenzene (5), which is then reduced to aniline (6). The aniline is
then converted to cyclo- hexanol (7), which is oxidized to cyclohexanone.
(c) Benzene is hydrogenated to cyclohexane (8), which is then oxidized to cyclohexanone (9).
The cyclohexanone produced by any of these routes is reacted with hydroxylamine (in the form
of its sulphate (NH2OH.H2S04), forming cyclohexanone oxime (10). Cyclohexanone oxime is
treated with sulphuric acid, and undergoes the Beckmann transformation to form caprolactam
(11).
(2) Cyclohexane Route
Benzene may be hydrogenated to cyclohexane (1), which is then nitrated (2). The nitro-
compound is reduced, forming cyclohexanone oxime (3), which is converted to caprolactam as
above.

8. (3) Cyclohexylamine Route
Aniline is hydrogenated to convert it to cyclohexylamine (1). Hydrogen peroxide is reacted with
this to form an addition compound, which is then converted to cyclohexanone oxime by
treatment with ammonium tungstate solution (2). The cyclohexanone oxime is converted to
caprolactam as above.
(4) Hexahydrobenzoic Acid Route
This is a process patented by Snia Viscosa for the production of caprolactam from toluene which
is available from petroleum refining. Toluene is oxidized to benzoic acid (1) which is
hydrogenated to hexahydrobenzoic acid (2). Treatment of this with nitrosyl sulphuric acid in the
presence of oleum produces caprolactam (3).
POLYMERIZATION
The polymerization of caprolactam is carried out usually by one or other of two processes, either
(a) a non-aqueous process, or

9. (b) an aqueous or hydrolytic process.
(a) Non-aqueous Process
In this process, the carprolactam is heated in the presence of catalysts (e.g. alkali metals and
their salts) at temperatures of up to 280°C. Polymerization proceeds by the opening of the
caprolactam rings and the linking of the opened rings into polymer molecules. The reaction is
rapid, and high molecular weight polycaproamide may be produced, e.g. with a degree of
polymerization in the region of 200. The polymers are highly crystalline. They are generally
superior in physical properties to polymers made by the alternative method, but the process is not
used, as a rule, in the production of fibres. It is of particular interest in the production of cast
polyamide plastics.
(b) Hydrolytic Process
This is the technique commonly adopted in the production of polycaproamide for fibre
manufacture. The process is usually operated on a continuous basis. Caprolactam, mixed with
about 10 per cent of its weight of water, together with dulling agents (where required), acid
catalyst and acid chain-stopper, are fed continuously into the top of a stainless steel column,
which may be 6 m (20 ft) high and 45 cm (18 in) diameter. The column is heated to 250-270°C,
and as the caprolactam flows downwards through the column it undergoes polymerization to
polycaproamide. An equilibrium condition is reached, the material at the base of the column
containing about 89-92 per cent of polymer and 11-8 per cent of caprolactam. The amount of
caprolactam in the equilibrium mixture depends upon the temperature; at 260°C, there is about
11 per cent.
The polymerization of caprolactam takes place via two routes, (a) a polycondensation reaction,
and (b) a polyaddition reaction.
Poly condensation Reaction
The water added to the caprolactam as it enters the reaction vessel acts as a hydrolytic agent,
reacting with some of the caprolactam to form 6-amino caproic acid.
Polycondensation of this acid then takes place, setting free water which forms more amino
caproic acid from caprolactam. This undergoes condensation, contributing to the polymerization,
and so the process goes on.

10. Polyaddition Reaction
The polyaddition reaction takes place through the opening of caprolactam rings, and the linking
together of the opened molecules. There is no intermediate formation of amino acid, and the
reaction does not involve the liberation of water or other small molecules. It is an addition
reaction, and not a condensation reaction. Polyaddition takes place alongside the
polycondensation reaction, both contributing to the creation of polymer molecules. Polyaddition
predominates over the polycondensation. Polymerization continues until the amino end groups
are blocked by the organic acid which was added to serve as a polymerization stabilizer, as in the
case of nylon 6.6 production.
Polycaproamide made in this way has a degree of polymerization which is commonly in the
region of 120-140. The molten polycaproamide may be spun directly at this stage, without any
intermediate isolation of solid polymer. More commonly, it is extruded from the pressure vessel
as a thick macaroni-like strand which is cooled by a water spray or by falling on to a cooled
metal band. The solidified polymer is chopped into small chips of maximum diameter about 6
mm (1/4 in).
The chips are washed in demineralized water, which dissolves out the bulk of the caprolactam;
they are then centrifuged and dried in vacuo at a temperature below 85 °C. The washed and dried
chips contain about 1 per cent of caprolactam.

11. POLYESTER FIBRES
PRODUCTION
Reactant Synthesis
(a) Ethylene Glycol
This is made by the catalytic oxidation of ethylene, which is obtained from petroleum cracking.
Ethylene oxide is produced (1). Hydration of this yields ethylene glycol (2).
(b) Terephthalic Acid; t Dimethyl Terephthalate
Para-xylene obtained from petroleum is oxidized (3), for example with nitric acid or with air in
the presence of a catalyst. Terephthalic acid is esterified with methyl alcohol (4) to form
dimethyl terephthalate.
POLYMERIZATION
Polyethylene terephthalate is made by the condensation of terephthalic acid, or a derivative such
as dimethyl terephthalate, with ethylene glycol.
Condensation of ethylene glycol with terephthalic acid (1) is an esterification reaction, water
being eliminated as the reaction takes place. Condensation of ethylene glycol with dimethyl
terephthalate (2) is an ester interchange reaction, methyl alcohol being eliminated as the reaction
takes place. The polymer obtained in this way would be expected to have an ester end group
instead of the carboxylic acid end group in the case of the polymer obtained by the terephthalic
acid route.

12. In either case, the condensation is carried out by heating the ethylene glycol and terephthalic acid
or dimethyl terephthalate and removing the water or methyl alcohol in vacuo. When the desired
degree of polymerization has been reached, the clear, colourless polyester is extruded through a
slot on to a casting wheel. The polymer solidifies into an endless ribbon, which is fed to a cutter
and cut into chips in the form of cubes with 3-6 mm (1/8- 1/4 in) sides.
The chips are despatched to the spinning
room via a suction pipe.
PRODUCTION ofPAN
Monomer Synthesis
Acrylonitrile is available in more than adequate quantity to meet the demands of the acrylic fibre
industry. It is made usually by any of four main routes.
(a) Ethylene Cyanhydrin Dehydration
Ethylene cyanhydrin is made either by treatment of ethylene oxide with hydrogen cyanide (1) or
by reaction of ethylene

13. chlorhydrin with alkali cyanides (2). The ethylene cyanhydrin is dehydrated (liquid phase) at
250-350°C. in the presence of alkaline catalyst, or (vapour phase) at 350°C. in the presence of
alumina (3).
(b) Acetylene and HCN
Acrylonitrile is made directly from acetylene by the addition of HCN.
POLYMERIZATION
The polymerization of acrylonitrile and its co-monomer is commonly carried out by stirring the
monomers with water in the presence of catalyst and surfactants. Some of the acrylonitrile
dissolves in the water to form a 7 per cent solution, the excess monomer forming an emulsion.
As polymerization proceeds, the polymer (which is insoluble in water) is precipitated to form a
slurry. This is filtered, and the polymer is washed and dried. Polymerization may be carried out
as a batch process, or on a continuous basis. In the latter case, monomer, water and other
materials are fed into a reaction vessel, and slurry is withdrawn continuously. Unreacted
monomer is recovered and returned to the polymerization.
PRODUCTION OF POLYETHYLENE
Monomer Synthesis
Ethylene
Ethylene is obtained from petroleum processing.

14. POLYMERIZATION
(a) High Pressure I High Temperature Process
Ethylene is polymerized by heating at temperatures in the region of 150-200°C, and pressures of
1,000-2,000 atmospheres. The reaction is promoted by traces of oxygen or other catalysts.
Polyethylene is produced in the form of a molten material which solidifies to a waxy solid.
Polymerization of ethylene by the high-pressure/high temperature process does not result in
straightforward linear molecules of polyethylene. The molecules are branched, and polymer
produced by this method may have as many as 30 branches for every 1,000 carbon atoms in the
molecular chain. Branching restricts the ability of polymer molecules to pack together, and
prevents them aligning themselves into the orderly patterns that make for regions of crystallinity.
Polyethylene made by high-temperature /high pressure polymerization is not highly crystalline.
(b) Low Pressure I Low Temperature Process
Ethylene is polymerized at much lower pressures and at temperatures below 100°C. A variety of
catalyst systems may be used. The process developed by Professor Karl Ziegler in 1953-54 made
use of organometallic compounds, e.g. of lithium, sodium and aluminium, in conjunction with a
small amount of transition metal compound, e.g. titanium tetrachloride.
The molecules of polymer from low-temperature polymerization processes, with fewer side
branches, are able to pack together more effectively than those from the high-temperature
process. The low-temperature polymers are more highly crystalline than those made by high-
temperature polymerization, and this affects the physical properties of the polymer. The density
of low-tempera- ture polymer, for example, is higher than that of the hightemperature polymer;
the long unbranched molecules of the former can pack closer together, so that the weight per unit
Volume is increased. Ziegler-type polyethylene has a density of 0.95, and Phillips-type
polyethylene of 0.96.
The density of the earlier type of polyethylene is 0.92.This difference in density is commonly
used in referring to the different forms of polymer. Polyethylene made by the
hightemperature/high-pressure (earlier) process is called Low-density Polyethylene;polymer
made by the low-temperature/low pressure (later) processes is called High-density Polyethylene.

15. PRODUCTION OF POLYPROPYLENE
The successful polymerization of ethylene, using organometallic catalysts, was followed by
attempts to use this type of catalyst for polymerizing other olefins, notably propylene.
Polypropylene of high molecular weight had been made in 1952 by Fontana, but the polymers
obtained were oils and greases. In 1954, Professor Giulio Natta of Milan Polytechnic, Italy,
discovered that certain Ziegler-type catalysts could bring about polymerization of propylene to
linear polypropylenes of high molecular weight.
Natta was able to separate his polypropylene into a number of polymers, using differences in
their solubility. He found that some polymers had a density as high as 0.91, whereas others were
as low as 0.85. They varied also in having different melting points, and some crystallized where
others remained amorphous. These differences were found even in polypropylenes of similar
molecular weights.
X-ray and infra-red investigations showed that the differences between the polypropylenes were
due to different steric structures of the polymers. Certain steric structures permitted an ordered
arrangement of the molecules into crystalline regions, providing the solid, high-melting, high-
density polypropylene; other molecular structures were incapable of packing together in this
orderly fashion, and these molecules formed the viscous, lowmelting, low-density
polypropylene.
Stereoregularity
The molecule of polypropylene consists of a long chain of carbon atoms, with methyl groups
forming appendages which stand out from the sides of the chain. This three-dimensional
structure of the molecule permits it to exist in a variety of forms which differ in their spatial
arrangements. Examples of different spatial arrangements in a polymer of an alpha-olefin such
as propylene.The backbone of the polymer molecule consists of a zig-zag chain of carbon atoms
which may be considered as lying in the plane of the paper. Every side-grouping (R) may then lie
in one of two positions; i! may be above the plane of the paper, or below it. Professor Natta
recognized that certain basic types of polymer structure were made possible by these alternative
positions of the side groups, and he gave them names by which they are now
generally known.

16. Stereospecific Polymerization Processes
The polymerization processes developed by Karl Ziegler, Giulio Natta and their colleagues were
important not only in providing linear polymers of propylene and other alpha-olefins, but in
establishing such control over the polymerization that polymers of desired steric structure could
be made. The process could be controlled to provide an isotactic polypropylene, or a syndiotactic
polypropylene, or an atactic polypropylene. The technique has become known as stereospecific
polymerization.
This remarkable development in polymer chemistry was achieved by using very special types of
catalyst and by controlling the reaction conditions with great care. The production of an isotactic
polymer, for example, requires not only regular 'head to-tail linking of the monomer molecules ,
but also a constant opening of the double bond (always cis or always trans) and constant
positioning of the monomer with respect to the plane in which the double bond lies.

17. The techniques used previously in polymerizing alpha-olefins could not bring about a
predetermined positioning of the monomer in relation to the growing chain. Regularity of
positioning is achieved only by accurate orientation of the monomer towards the catalysts at the
stage immediately preceding its addition to the growing chain.
The catalysts used by Ziegler in the low-temperature polymerization of ethylene made possible
the first stereospecific techniques. Ethylene itself is a symmetrical molecule, and the linear
polyethylene molecule does not display steric differences of the isotactic, syndiotactic and atactic
type. Also, ethylene is a more reactive substance than propylene and the higher olefins, and the
Ziegler catalysts used for polymerizing ethylene do not necessarily polymerize propylene at all,
much less polymerize it to a stereoregular polymer in high yield. Before the discovery of
stereospecific polymerization, the only linear polyolefins of high molecular weight which could
be made were those derived from olefins with a symmetrical structure (ethylene, isobutylene).
But the new sterically-controlled polymerization processes make possible the polymerization of
olefins higher that ethylene, and the copolymerization of these with ethylene. High molecular
weight products are obtained which, depending upon their structure and composition, may be of
commercial value.