Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR THE PREPARATION OF POLYMER PARTICLES
The present invention relates to a process for the
preparation of polymer particles containing a polymer of
a vinylarene monomer and a physical foaming agent, and to
such polymer particles.
Particles that contain such a polymer and foaming
agent are generally known as expandable polymer
particles. A well-known type of expandable polymer
particles is expandable polystyrene. Expandable
polystyrene is produced on a commercial scale by
suspension polymerization. The foaming agent is usually a
low-boiling hydrocarbon, such as a C3-Cg hydrocarbon, in
particular pentane isomers. The expandable polystyrene is
used for making foamed articles that are produced by
expanding the polystyrene particles. In the expansion
process the hydrocarbon foaming agent is released and may
be emitted into the environment. Such emissions are
regarded undesirable and ways are sought to avoid such
emissions. One way is to recover or burn the emitted
hydrocarbon. Another way is to reduce the amount of
hydrocarbon foaming agent in the expandable polymer
particles.
In US-A-5,096,931 expandable polystyrene is described
which contains polystyrene, a small amount of a polar
polymer, some water and a reduced amount of hydrocarbon
foaming agent. Although the content of hydrocarbon
foaming agent has been reduced such agent must still be
present to achieve satisfactory expansion.
GB-A-1,106,143 discloses a process for preparing
water-expandable polystyrene particles by mixing by
vigorous mechanical agitation styrene monomer, water and
an emulsifier with a free-radical initiator to obtain an
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emulsion containing small droplets of water. Subsequently, the emulsion is
suspended
in an aqueous phase and the suspension obtained is subjected to
polymerisation. In order
to achieve a satisfactory expansion certain amounts of organic foaming agents
are
included.
In experiments to verify the merits of the teaching of the above GB patent it
was found
that the finely dispersed water droplets obtained in the first emulsion tend
to coalesce
and form bigger droplets during polymerisation. In an experiment in GB-A-
1,106,143 it
is confirmed that droplets bigger than 40p.m cause unsatisfactory foamed
articles after
expansion. Vigorous agitation is apparently necessary in this known-process to
create
and maintain the finely dispersed water droplets. However, it is awkward to
stir in
commercial operation at such high energy input.
Hence, it would be desirable if the tendency of the water droplets to coalesce
could be
reduced.
Surprisingly, it was found that the tendency for the water droplets to grow
could be
reduced by creating a water-containing emulsion before completely polymerising
the
vinylarene monomer in suspension polymerisation. This makes it furthermore
possible
to stir less vigorously when emulsifying the water in the (partly polymerised)
vinylarene
monomer. Stirring can be carried out at an energy input equivalent to or less
than 500
rotations per minute for a 701 reactor, even at an energy input equivalent to
or less than
350 rotations per minute for a 701 reactor.
Accordingly, the present invention provides a process for the preparation of
polymer
particles containing a vinylarene polymer by suspension polymerisation, which
process
comprises:
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a) pre-polymerising vinylarene monomers to a conversion
degree of 20 to 700, based on the vinylarene monomer, to
yield a pre-polymerised mass, which pre-polymerised mass
further contains water emulsified therein and an
emulsifier, which pre-polymerisation is carried out with
water already present or before water is added;
b) suspending the pre-polymerised mass in an aqueous
medium to yield suspended droplets; and
c) polymerising the vinylarene monomer in the suspended
droplets to complete monomer conversion to yield
suspended polymer particles.
A pre-polymerised mass differs from a mixture of
polymerised vinylarene and vinylarene monomer, in that
the first has a monomodal molecular weight distribution
while the latter will in general have a bimodal
distribution. For many applications, the latter will be
disadvantageous in that the physical properties of the
material will vary over a wider range. In order to obtain
a monomodal distribution for a mixture of polymerised
vinylarene and vinylarene monomer, the process conditions
will have to be controlled very strictly. This is
unattractive for commercial operations.
It is thought that the good results obtained in the
process of the present invention, are due to the creation
of the viscous pre-polymerised mass in which water has
been emulsified before suspending the vinylarene in an
aqueous medium for suspension polymerisation. The water
droplets emulsified are rendered less mobile so that
there is little tendency for them to coalesce or to move
into the aqueous suspension medium.
The present process is capable of yielding polymer
particles with satisfactory expandability properties that
do not contain an organic foaming agent. The process is
therefore preferably conducted in the substantial
~i~vryVDFD SHEET
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absence of C3-C6 hydrocarbon foaming agent. In the
substantial absence means in an amount less than 0.5 owt
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based on the amount of vinylarene monomer, preferably
less than 0.25 owt, more preferably in the complete
absence of such foaming agents.
In a further embodiment of the invention the polymer
particles obtained are separated from the aqueous mixture
and, optionally, expanded to yield pre-expanded particles
which are optionally treated further to yield foamed
articles.
The creating of the viscous, pre-polymerised mass is
preferably carried out by bulk polymerisation of the
vinylarene monomer to the desired degree. The emuls ~fi-
cation of water in the starting monomer can be achieved
in various ways. In one embodiment, the water, an
emulsifier and the vinylarene monomer are stirred to
create an emulsion which is subsequently subjected to
pre-polymerisation to the desired conversion degree to
yield a pre-polymerised mass. In another embodiment, the
vinylarene monomer is first subjected to pre-polymerisa-
tion, and subsequently, water and emulsifier are added to
the (partially) pre-polymerised vinylarene mixture and
water is emulsified. A third embodiment comprises pre-
polymerisation of vinylarene monomer in the presence of
emulsifier, and subsequently adding the water to be
emulsified. In a fourth embodiment, emulsifier is
prepared in-situ in the presence of water, and
subsequently vinylarene monomer is added to the
emulsifier obtained.
The emulsifiers are preferably compatible (soluble)
with the vinylarene. The emulsifier may be selected from
a wide range of compounds. Preferably, the emulsifier is
of the type which gives water-in-oil emulsions. The
emulsifier can be a non-ionic, an anionic or a cationic
surfactant.
Suitable emulsifiers include nonionic surfactants
such as sorbitan carboxylates, sorbitol or mannitol
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carboxylates, glycol or glycerol carboxylates, alkanol-
amides, alkyl phenols and dialkyl ethers. Any of these
emulsifiers may contain a polyalkoxy chain with 1 to 20
oxyalkylene groups, such as oxyethylene or oxypropylene
moieties. Suitable anionic emulsifiers include salts of
long chain (Cg-C30)carboxylic acids, long chain (Cg-30)
alkyl sulphonic acid, alkylarylsulphonic acid,
sulphosuccinic acid. The cation of these emulsifiers may
suitably be an ammonium moiety or an alkali or alkaline
earth metal ion. Suitable cationic surfactants can be
selected from high-molecular-weight fatty amines,
ammonium or other nitrogen derivatives of long chain
carboxylic acids. The anionic and cationic emulsifiers
may contain a polyoxyalkyl group. Good results-have been
obtained with bisalkylsulphosuccinates, sorbitol-Cg_20-
carboxylates and/or Cg_20-alkylxylene sulphonates.
Preferred are the metal salts of bis(2-ethylhexyl)-
sulphosuccinic acid.
The amount of the emulsifier to be used is to some
extent dependent on the amount of water to be emulsified.
Suitably, the amount of emulsifier ranges from 0.01 to
5 %wt, based on the amount of vinylarene monomer in the
emulsion. Preferred ranges are from 0.1 to 3, more
preferred from 0.2 to 1.5 %wt.
The amount of water to be emulsified which to some
extent determines the desired amount of emulsifier, can
be chosen between wide ranges. Suitably the amount of
water ranges from 1 to 20 %wt, based on the weight of
vinylarene monomer and water. Well-expandable particles
can be obtained when from 3 to 15 %wt of water is
emulsified. Below 1 %wt the expandability may be too low,
whereas at very high water contents the particles can
yield expanded articles that may run the risk of
collapsing.
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In the water to be emulsified an electrolyte may be
included. Suitable electrolytes are alkali and alkaline
earth salts, but other inorganic salts may equally well
be used. The electrolyte may lead to a decrease in
droplet size and may enhance the water-in-oil character
of ionic surfactants. Therefore, it may be advantageous
to use a water phase with from 0.5 to 5 %wt of
electrolyte, based on amount of water, especially when an
ionic emulsifier is used. Preferred salts are alkali
metal halides, such as NaCl and KCl.
The pre-polymerisation step may be conducted in any
known manner. This includes free-radical polymerisation
and thermal radical polymerization. Thermal poly-
merisation can be effected by heating the emulsion to a
temperature of 120 to 150 °C. When the desired conversion
has been achieved the temperature is reduced. If the pre-
polymerisation step is carried out by thermal radical
polymerisation with water already present, the pre-
polymerisation needs to be carried out at elevated
pressure. If the pre-polymerisation step is carried out
by thermal radical polymerisation before water is added,
the pre-polymerised mass will generally be cooled before
adding water. This makes that in most cases it is
preferred to pre-polymerise by free-radical poly-
merisation with the help of one or more free-radical
initiators. For the same reasons, the polymerisation step
c) is preferably conducted by free-radical poly-
merisation. Pre-polymerisation by means of free-radical
polymerisation can be carried out by adding an initiator
to the vinylarene/water emulsion and starting the
polymerisation by heating to 40-140 °C. The pre-
polymerisation of step a) is preferably carried out by
heating to 40-120 °C. The polymerisation of step c) is
preferably carried out by heating to 60-140 °C. The free-
radical polymerisation is suitably carried out at a
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pressure of 0.5 to 5 bar, preferably 0.7 to 1.5 bar, more
preferably at atmospheric pressure. The further process
conditions are well-known to the skilled artisan. Most
preferably, the final stage of the polymerisation of
step c) is carried out at elevated pressure and at a
temperature of 110-140 °C in order to further reduce the
amount of monomer present in the final product.
Optimal conversion degrees of the pre-polymerised
mass may vary for different monomers. Suitably, the
conversion varies between 20 and 700 of the vinylarene
monomer.
If the conversion is higher than 70%, the viscosity
of the pre-polymerised mass may be so high that handling
problems may occur. This can complicate suspending the
pre-polymerised mass in the aqueous phase or emulsifica-
tion of water into the pre-polymerised mass. If the pre-
polymerisation degree is lower than 200, the suspended
droplets will tend to be unstable. In that case,
undesirably large amounts of aqueous suspension medium of
large droplet size will be incorporated. This will lead
to foam collapse during expansion. Preferably, the
conversion varies between 30 and 600.
In order to improve the expansion properties of the
eventual polymer particles it is preferred to have cross-
linking agent present during polymerisation. The cross-
linking agent can be added in step a) and/or in step c).
Preferably, the cross-linking agent is added in step a).
Suitably, the cross-linking agent is selected from the
group of compounds having at least two olefinic double
bonds. Examples of such compounds include divinylbenzene,
a,,u~-alkadienes, e.g. isoprene, the diester of acrylic
acid or methacrylic acid with a diol, such as butanediol,
pentanediol or hexanediol. Preferred for its com-
patibility with the vinylarene is divinyl-benzene.
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In order to obtain a significant cross-linking effect
the amount of the cross-linking agent should not be too
low. On the other hand, if the amount of cross-linking
agent would be too high, the expandability of the
eventual particles would be deteriorated. A suitable
range is from 0.01 to 5 %wt, preferably from 0.01 to
1.5 owt, based on the amount of vinylarene monomer. Most
preferably from 0.01 to 0.5 %wt of cross-linking agent is
used.
Further, it has been found to be advantageous to
polymerise the vinylarene monomer in the presence of a
polyphenylene ether. The presence of polyphenylene ether
reduces the chance that the foamed material collapses
during cooling. Suitable polyphenylene ethers have been
described in EP-A-350137, EP-A-403023 and EP-A-391499.
The polyphenylene ether can be added in step a) and/or in
step c). Preferably, the polyphenylene ether is added in
step a). The polyphenylene ether compound preferably is
present in an amount of between 1 and 30 owt, based on
amount of vinylarene.
Subsequent to the pre-polymerisation step, the pre-
polymerised mass is suspended in an aqueous medium. The
volume ratio between the aqueous suspension medium and
the pre-polymerised mass may vary between wide ranges, as
will be appreciated by a person skilled in the art.
Suitable volume ratios include 1:1 to 1:10 (pre-
polymerised mass:aqueous phase). The optimal ratio is
determined by economic considerations.
The aqueous medium may contain one or more
conventional stabilizing agents, such as polyvinyl-
alcohol, gelatine, polyethyleneglycol, hydroxyethyl-
cellulose, carboxymethylcellulose, polyvinylpyrrolidone,
polyacrylamide, but also salts of poly(meth)acrylic acid,
phosphonic acid or (pyro)phosphoric acid, malefic acid,
ethylene diamine tetracetic acid, and the like, as will
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be appreciated by the person skilled in the art. Suitable
salts include the ammonium, alkali metal and alkaline
earth metal salts. An advantageous example of such a salt
is tricalcium phosphate. Preferably, the stabilizing
agent is based on acrylic acid and/or methacrylic acid,
optionally in combination with acrylic amide. The amount
of the stabilizing agents may suitably vary from 0.05 to
1, preferably from 0.15 to 0.6 owt, based on the weight
of the aqueous medium.
For the same reasons as apply to pre-polymerisation
step a), the polymerisation step c) is advantageously
effected by free-radical polymerisation by means of one
or more free-radical initiators.
The polymerisation can be further improved-by
increasing the stability of the suspension. Such a
stability increase can be effected by incorporation of a
polar polymer into the pre-polymerised mass in addition
to the emulsifying agent already present. Examples of
such polymers are polyvinylalcohol, gelatine, poly-
ethyleneglycol, hydroxyethylcellulose, carboxy-
methylcellulose, polyvinylpyrrolidone, polyacrylamide,
but also salts of poly(meth)acrylic acid, phosphonic acid
or (pyro)phosphoric acid, malefic acid, ethylene diamine
tetracetic acid. Suitable salts include the ammonium,
alkali metal and alkaline earth metal salts. Preferably,
the stabilizing polar polymer is based on acrylic acid
and/or methacrylic acid, optionally in combination with
acrylic amide. The incorporation may be effected by
mixing the polar polymer with the pre-polymerised mass,
but it may also be incorporated in-situ by mixing the
corresponding polar monomer with the vinylarene monomer
and water and polymerising the polar monomer to yield the
polar polymer desired. Subsequently, the polar polymer
may be suspended together with the other components of
the pre-polymerised mass. Another way to incorporate the
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polar polymer is to add the corresponding polar monomer
to the pre-polymerised mass and subsequently polymerise
the monomers to yield the polar polymer. The amount of
polar polymer is suitably from 0.1 to loo by weight,
based on water emulsified.
The free-radical initiator can be selected from the
conventional initiators for free-radical styrene
polymerization. They include in particular organic peroxy
compounds, such as peroxides, peroxycarbonates and
peresters. Combinations of peroxy compounds can also be
used. Typical examples of the suitable peroxy initiators
are C6-C20 acyl peroxides such as decanoyl peroxide,
benzoyl peroxide, octanoyl peroxy, stearyl peroxide,
3,5,5-trimethyl hexanoyl peroxide, per-esters of C2-C18
acids and C1-C5 alkyl groups, such as t-butylperbenzoate,
t-butylperacetate, t-butyl-perpivalate, t-butylperiso-
butyrate and t-butyl- peroxylaurate, and hydroperoxides
and dihydrocarbyl (C3-C10)peroxides, such as diiso-
propylbenzene hydroperoxide, di-t-butyl peroxide, dicumyl
peroxide or combinations thereof.
Radical initiators different from peroxy compounds
are not excluded. A suitable example of such a compound
is a,a.'-azobisisobutyronitrile. The amount of radical
initiator is suitably from 0.01 to 1 owt, based on the
weight of the vinylarene monomer. The process is suitably
initiated by heating the reaction mixture to elevated
temperature, e.g., in the range of 40 to 140 °C.
The polymerisation process may suitably be carried
out in the presence of a chain transfer agent. The person
skilled in the art will appreciate that these chain
transfer agents can be selected from mercaptans, such as
C2-C15-alkyl mercaptans, e.g. n-dodecylmercaptan,
t-dodecylmercaptan, n-butyl mercaptan or t-butyl-
mercaptan. Preferred are aromatic compounds such as
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pentaphenyl ethane, and in particular the dimer of a-
methyl styrene.
The present invention has enabled the skilled artisan
to prepare water-foamable particles that contain water as
foaming agent. Accordingly, the present invention
provides expandable polymer particles comprising a
polymer of a vinylarene monomer, water in the form of
droplets, and an emulsifier, in which the amount of water
ranges from 8.6 to 15 %wt, based on the total weight of
the polymer particles. The polymer particles do not need
to contain C3-C6 hydrocarbon foaming agent. This means
that the hydrocarbon foaming agent can be present in an
amount less than 0.5 %wt based on total amount of polymer
particles, preferably less than 0.25 owt, more preferably
in the complete absence of such foaming agents.
The polymer particles may further contain several
additives or coatings in effective amounts. Such
additives include dyes, fillers, stabilisers, flame
retarding compounds, nucleating agents, antistatic
compounds and lubricants. Of particular interest are
coating compositions containing glycerol- or metal
carboxylates. Such compounds reduce the tendency of the
particles to agglomerate. Suitable carboxylates are
glycerol mono-, di- and/or tristearate and zinc stearate.
Examples for such additive composition are disclosed in
GB-A-1,409,285. The coating composition are deposited
onto the particles via known methods e.g. via dry-coating
in a ribbon blender or via a slurry or solution in a
readily vaporising liquid.
The particles have advantageously an average diameter
of 0.1 to 6 mm, preferably from 0.4 to 3 mm.
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The expandable particles can be prefoamed by hot air
or by using (superheated) steam, to yield expanded or
pre-expanded particles. Such particles have a reduced
density, e.g. from 800 to 30 kg/m3. It will be
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appreciated that in order to vapourise the water included in the particles to
effect
foaming, the temperature must be higher than used for C3 -C6 hydrocarbon
foaming
agents which have a lower boiling point than water. Foaming can also be
effected by
heating in oil or by microwaves.
The invention will be further illustrated by means of the following examples.
EXAMPLE 1
In an autoclave of 2 litres, an amount of styrene was mixed with 0.4% wt,
based on
styrene, of dibenzoyl peroxide and 0.15% wt, based on styrene, of tent-butyl
peroxybenzoate together with l Og of sodium bis(2-ethylhexyl)sulphosuccinate
(sold
under the trade mark "AOT") under nitrogen at a stirring rate of 300 rpm. The
mixture
was subsequently polymerised by heating to 90°C. for 100 minutes. The
conversion
degree of styrene was about 55%. Water containing 0.9% wt of sodium chloride
was
slowly added to the pre-polymerised mass whilst stirring at 800 rpm. The
stirring was
continued for 5 minutes. In a 6.4 litres autoclave, the emulsion thus obtained
was m
suspended in water containing 0.4% by weight of hydroxyethyl cellulose sold
under the
trade mark "NATROSOL 250G" by the Dutch company "AQUALON". The weight
ratio of water to pre-polymerised mass was about 3:1. The polymerisation
reaction was
continued at 90°C. for 5 hr. The nitrogen pressure was increased to 4
bar and the
temperature was increased to 125°C. The suspension was maintained at
these conditions
for a further 5 hours to complete the polymerization. The polymer beads were
separated
from the water phase, and washed with water. The water content of these beads,
based
on amount of polystyrene, water and emulsifier, was determined by TGA (thermal
gravimetric analysis). The beads were expanded in hot air of 130°C. in
a 500 ml glass
vessel with the help of a hot air gun. The results
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are indicated in Table 1 below. The expandability is
expressed as ratio of expanded volume of the beads to
volume of the beads before expansion.
Exp. Starting Polymer beads
No. material,
g
Styrene AOT water water content, expand-
owt ability
1.1 940 6 60 8.6 11.4'
1.2 920 8 80 9.3 13.6
1.3 900 10 100 11.3 13.9
COMPARATIVE EXAMPLE
In an autoclave of 2 litres, 900 g of styrene was
mixed with 0.4 %wt, based on styrene, of dibenzoyl
peroxide and 0.15 %wt, based on styrene, of tert-butyl
peroxybenzoate together with 10 g of sodium bis(2-ethyl-
hexyl)sulphosuccinate (sold under trade mark "AOT") under
nitrogen at a stirring rate of 300 rpm. Slowly 100 g of
water containing 0.9 owt of sodium chloride was added
whilst stirring at 800 rpm. The stirring was continued
for 5 minutes. In a 6.4 litres autoclave, the mixture
thus obtained was suspended in 3 1 water containing 0.40
by weight of hydroxyethyl cellulose sold under the trade
mark "NATROSOL 2506". The weight ratio of water to
styrene containing mass was about 3:1. It was observed
that no separate droplets could be seen. This is probably
due to the fact that an oil-in-water emulsion had been
formed. The polymerisation reaction was continued at
90 °C. After approximately 2 hours, the stirrer of the
reactor stalled. When the reactor was opened it was found
that the emulsion had changed into a solid, white lump
and water.
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EXAMPLE 2
In a vessel of 6 litres, 3600 g of styrene was mixed
with 0.4 owt, based on styrene, of dibenzoyl peroxide and
0.15 %wt, based on styrene, of tert-butyl peroxybenzoate
together with 40 g of sodium bis(2-ethylhexyl)sulpho-
succinate (sold under trade mark "AOT") under nitrogen at
a stirring rate of 300 rpm. The mixture was subsequently
polymerised by heating to 90 °C for 100 minutes. The
conversion degree of styrene was about 550.
Slowly, 400 g of water containing 0.9 %wt of sodium
chloride was added whilst stirring at 800 rpm. The
stirring was continued for 5 minutes. In a 10 litres
autoclave, the emulsion thus obtained was suspended in
4 1 water containing 0.4o by weight of hydroxyethyl
cellulose sold under the trade mark "NATROSOL 2506". The
weight ratio of suspension water to pre-polymerised mass
was about 1:1. The polymerisation reaction was continued
at 90 °C for 5 hr while stirring at 350 rpm. The nitrogen
pressure was increased to 4 bar and the temperature was
increased to 125 °C. The suspension was maintained at
these conditions for a further S hours to complete the
polymerization. The polymer beads were separated from the
water phase, and washed with water. The water content of
these beads, based on amount of polystyrene, water and
emulsifier, was determined by TGA. The beads were
expanded in hot air in a 500 ml glass vessel with the
help of a hot air gun. The results are indicated in
Table 2 below.
EXAMPLE 3
In an autoclave of 2 litres, 900 g styrene was mixed
with 0.4 owt, based on styrene, of dibenzoyl peroxide and
0.15 %wt, based on styrene, of tert-butyl peroxybenzoate
together with 10.0 g sorbitan tristearate (sold under the
trade mark "SPAN 65") under nitrogen at a stirring rate
of 300 rpm. The mixture was subsequently polymerised by
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heating to 90 °C for 100 minutes. The conversion degree
of styrene was about 550. Slowly, 100 g of water
containing 0.9 %wt of sodium chloride was added whilst
stirring at 800 rpm. The stirring was continued for
5 minutes. In a 6.4 1 autoclave, the emulsion thus
obtained was suspended in 3 1 water containing 0.4% by
weight of hydroxyethyl cellulose sold under the trade
mark "NATROSOL 2506". The weight ratio of water to pre-
polymerised mass was about 3:1. The polymerisation
reaction was continued at 90 °C for 5 hr. The nitrogen
pressure was increased to 4 bar and the temperature was
increased to 125 °C. The suspension was maintained at
these conditions for a further 5 hours to complete the
polymerization. The polymer beads were separated from the
water phase, and washed with water. The water content of
these beads, based on amount of polystyrene, water and
emulsifier, was determined by TGA. The beads were
expanded in hot air in a 500 ml glass vessel with the
help of a hot air gun. The results are indicated in
Table 2 below.
EXAMPLE 4
In an autoclave of 2 litres, 900 g styrene was mixed
with 0.4 owt, based on styrene, of dibenzoyl peroxide and
0.15 %wt, based on styrene, of tert-butyl peroxybenzoate
together with 10.0 g sorbitan monooleate (sold under the
trade mark "SPAN 80") under nitrogen at a stirring rate
of 300 rpm. The mixture was subsequently polymerised by
heating to 90 °C for 100 minutes. The conversion degree
of styrene was about 55%. Slowly, 100 g of water
containing 0.9 owt of sodium chloride was added whilst
stirring at 800 rpm. The stirring was continued for
5 minutes. In a 6.4 1 autoclave, the emulsion thus
obtained was suspended in 3 1 water containing 0.4o by
weight of hydroxyethyl cellulose sold under the trade
mark "NATROSOL 2506". The weight ratio of water to pre-
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polymerised mass was about 3:1. The polymerisation
reaction was continued at 90 °C for 5 hr. The nitrogen
pressure was increased to 4 bar and the temperature was
increased to 125 °C. The suspension was maintained at
these conditions for a further 5 hours to complete the
polymerization. The polymer beads were separated from the
water phase, and washed with water. The water content of
these beads, based on amount of polystyrene, water and
emulsifier, was determined by TGA. The beads were
expanded in hot air in a 500 ml glass vessel with the
help of a hot air gun. The results are indicated in'
Table 2 below.
EXAMPLE 5
In an autoclave of 2 litres, 900 g styrene-was mixed
with 10.0 g of sodium bis(2-ethylhexyl)sulphosuccinate
(sold under trade mark "AOT"). The mixture was heated to
60 °C. 99 g of distilled water, 1 g of acrylic acid and
0.03 g potassium persulphate were slowly added to the
mixture whilst stirring at 800 rpm. The stirring was
continued for 5 minutes. The emulsion obtained was heated
to 60 °C for 3 hours to allow the acrylic acid to
polymerize, whilst stirring at 800 rpm.
To this were added, 0.4 owt of dibenzoyl peroxide,
based on styrene, and 0.15 owt of tert-butyl peroxy-
benzoate, based on styrene, and the temperature was
raised to 90 °C. This temperature was maintained for
100 minutes. The conversion degree of styrene was about
550. In a 6.4 litres autoclave, the emulsion thus
obtained was suspended in 3 1 water containing 0.4% by
weight of hydroxyethyl cellulose sold under the trade
mark "NATROSOL 2506". The volume ratio of suspension
water to pre-polymerised mass was about 3:1. The
polymerisation reaction was continued at 90 °C for 5 hr
while stirring at 350 rpm.' The nitrogen pressure was
increased to 4 bar and the temperature was increased to
CA 02258306 1998-12-15
WO 98!01489 PCT/EP97/03608
- 17 -
125 °C. The suspension was maintained at these conditions
for a further 5 hours to complete the polymerization. The
polymer beads were separated from the water phase, and
washed with water. The water content of these beads,
based on amount of polystyrene, water and emulsifier, was
determined by TGA. The beads were expanded in hot air in
a 500 ml glass vessel with the help of a hot air gun. The
results are indicated in Table 2 below.
EXAMPLE 6
In an autoclave of 2 litres, 900 g styrene was mixed
with 0.45 g of divinylbenzene, 0.4 %wt of dibenzoyl-
peroxide, based on styrene, and 0.15 %wt of tert-butyl
peroxybenzoate, based on styrene, and 10.0 g of sodium
bis(2-ethylhexyl)sulphosuccinate (sold under trade mark
"AOT"). The mixture was heated to 90 °C during
100 minutes, and stirred at 300 rpm. 100 g of distilled
water containing 0.9 owt of sodium chloride was slowly
added whilst stirring at 800 rpm. The stirring was
continued for 5 minutes. The conversion degree of styrene
was about 550. In a 6.4 litres autoclave, the emulsion
thus obtained was suspended in 3 1 water containing 0.40
by weight of hydroxyethyl cellulose sold under the trade
mark "NATROSOL 2506". The polymerisation reaction was
continued at 90 °C for 5 hr while stirring at 350 rpm.
The nitrogen pressure was increased to 4 bar and the
temperature was increased to 125 °C. The suspension was
maintained at these conditions for a further 5 hours to
complete the polymerization. The polymer beads were
separated from the water phase, and washed with water.
The water content of these beads, based on amount of
polystyrene, water and emulsifier, was determined by TGA.
The beads were expanded in hot air in a 500 ml glass
vessel with the help of a hot air gun. The results are
indicated in Table 2 below.
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Exp. Additive Polymer beads
no.
water expandability
content owt (measured at)
2 AOT 11.3 17 (135C)
3 SPAN 65 11.5 13 (130C)
4 SPAN 80 12.2 11 (130C)
AOT/acrylic acid 12.3 14 (135C)
6 AOT/divinylbenzene 12.0 15 (140C)
