The present invention relates to a process for the preparation of
expandable polystyrene and to expandable polystyrene obtainable by such 5 a
process.
A known method for producing expandable polystyrene polymers,
hereinafter referred to as EPS, is by aqueous suspension polymerization. It is
typically a batch process where two or more monomer-soluble polymerization
10 initiators are used with a rising stepwise, continuous, or combination
temperature profile. Initiators for the process are selected on the basis of their
half life temperatures to provide a measured supply of radicals at selected
points along the temperature profile such that effective conversion occurs
within an acceptable period of time. For styrene polymerization, it is convenient
15 to describe initiator decomposition performance in terms of one hour half life
temperature, defined as that temperature sufficient to cause decomposition of
one half of the starting concentration of initiator over a one hour time period.
Traditionally, suspension polymerization to prepare EPS is
conducted in a process using two different temperature stages and two
20 initiators, a first stage initiator and a second stage or “finishing” initiator, with
different half life temperatures, each appropriate for the particular temperature
stage. In such a process, dibenzoyl peroxide (BPO) is often used as the first
stage initiator at a reaction temperature of about 82°C to 95°C. Other first stage
initiators useful in this temperature range might include tertiary butyl peroxy-2-
25 ethylhexanoate, tertiary amyl peroxy-2-ethylhexanoate and 2,5-dimethyl-2,5-
di(2-ethylhexanoylperoxy)hexane. Initiators such as tertiary butyl
peroxybenzoate (TBP) or dicumyl peroxide (DCP) are widely used for the
higher temperature stage, or second stage, at 115°C to 135°C. The second
stage is usually a finishing step intended to minimize residual monomer in the
30 EPS. In commercial processing, this stage is often held above 125°C for
prolonged intervals to reduce monomer content to acceptable levels.
Characteristic shortcomings of the traditional process are long
reaction times necessary to obtain adequate conversion in the first stage and
relatively high finishing temperatures required in the second stage.
35 In view of alleviating this drawback, document US 6, 608, 150 has
proposed an improved process for the preparation of expandable polystyrene in
3
which “intermediate” temperature peroxides, that is to say initiator peroxides
having a one hour half life temperature ranging from 101°C to 111°C, are used.
According to this document, the use of such “intermediate” peroxides in the
preparation of expandable polystyrene allows to reduce the conversion time for
some hours5 .
Expandable polystyrene, as prepared in the suspension process, is
in the form of essentially spherical beads. It is mentioned in US 6, 608, 150 that
some blowing agent, such as pentane, may be used in the process in order to
render the polystyrene beads expandable.
10 However, it is known that the use of pentane in a process of
preparation of expandable polystyrene leads to a decrease in the molecular
weight as a result of transfer mechanism on the alkane agent (see Principles of
Polymerization-George Odian p 203-217,McGraw-Hill Book Company 1970).
Additionally, it is more and more requested in the industry that the
15 polystyrene resins comprise flame retardant additives for safety reasons. For
instance, flame retarded resins are widely used in insulation applications. The
addition of such additives may also lead to a decrease of the molecular weight
of the resulting polystyrene.
It appears then that several factors may lead, in the preparation
20 process of expandable polystyrene, to a significant decrease of the molecular
weight of such expandable polystyrene.
By “molecular weight” is meant according to the present application
the weight average molecular weight (Mw). According to the present invention,
the molecular weight is measured according to the SEC (Size Exclusion
25 Chromatography) method using Polystyrene standards.
It is important that the expandable polystyrene has a high molecular
weight in order to guarantee the mechanical properties of the final materials.
The Applicant has now discovered that by using a specific initiator
peroxide, it was possible to accelerate the preparation of expandable
30 polystyrene while using a blowing agent and to still obtain polystyrene having a
particularly high molecular weight.
The Applicant has also discovered that the continuous addition of
said specific initiator peroxide during the polymerization reaction, can also
accelerate the preparation of expandable polystyrene.
35 A first aspect of the invention relates to a process for the
preparation of expandable polystyrene comprising the following steps :
4
- i) a) preparing an aqueous suspension comprising styrene
monomer
- i) b) heating the suspension at a polymerisation temperature
ranging from 100°C to 120°C,
- i) c) adding continuously, before, during and/or after step i) b) a5 t
least one organic peroxide initiator of formula (I) 1-alkoxy-1-talkylperoxycyclohexane
in which the alkoxy group contains 1 to 4 carbon
atoms, the t-alkyl group contains 4 to 12 carbon atoms, and the cyclohexane
ring may optionally be substituted with 1 to 3 alkyl groups each, independently
10 having 1 to 3 carbon atoms,
- ii) adding a blowing agent selected from the group consisting of
alkanes having from 4 to 6 carbon atoms and mixtures thereof.
The process according to the invention allows obtaining
15 expandable polystyrene showing high molecular weight. Preferably, the
expandable polystyrene obtainable according to the process of the invention
shows a molecular weight (Mw) of at least 170, 000 g/mol, preferably of at least
175, 000 g/mol, and more preferably of at least 190, 000 g/mol.
Because of its high molecular weight, the expandable polystyrene
20 according to the invention may be used efficiently in insulation or packaging
applications.
Moreover, the process of the invention has a conversion time
reduced compared to the ones of the prior art.
The process of the invention uses at least one organic peroxide
25 initiator of formula (I), ie 1-alkoxy-1-t-alkylperoxycyclohexane in which the
alkoxy group contains 1 to 4 carbon atoms, the t-alkyl group contains 4 to 12
carbon atoms, and the cyclohexane ring may optionally be substituted with 1 to
3 alkyl groups each, independently having 1 to 3 carbon atoms.
According to the present invention, it has been found that the use of
30 such a specific organic peroxide of formula (I) in combination with a blowing
agent such as an alkane having from 4 to 6 carbon atoms and mixtures thereof
allowed to obtain expandable polystyrene having a high molecular weight, in a
short time. Such a result could not be obtained with other organic peroxides,
having a one hour half life temperature similar to that of compounds of formula
35 (I) but having a chemical formula different than formula (I).
5
As organic peroxides of formula (I) one can cite 1-alkoxy-1-tamylperoxycyclohexane
and 1-alkoxy-1-t-hexylperoxycyclohexane, where the
alkoxy group contains 1 to 4 carbon atoms, and the cyclohexane ring may
optionally be substituted with 1 to 3 alkyl groups each, independently having 1
to 3 carbon atoms5 .
In an embodiment of the invention, the at least one organic
peroxide initiator is 1-methoxy-1-t-amylperoxycyclohexane (also referred
hereinafter as TAPMC).
10 In a preferred embodiment of the process according to the
invention the polymerization mixture is formulated at a temperature below the
reaction (polymerization) temperature and subsequently heated to reach said
desired reaction temperature. In such a process preferably at most 40% by
weight (%w/w), more preferably at most 30 to 20% by weight, and most
15 preferably at most 5% by weight of the organic peroxide, based on the total
weight of the peroxide used during the polymerization, is present before step
I°)b) at the start of the heating-up phase, while the remainder is added
continuously over a period of at least 1, preferably 2, and more preferably 2-4
hours during or after step I°)b), depending on the polymerization time. More
20 preferably, the remainder of the peroxide is added from the time the reaction
mixture temperature is controlled at the desired reaction temperature.
The use of a small amount of peroxide from the start allows a fast heating up
and start of the polymerization, since this peroxide will already (partly)
25 decompose during the heating of the polymerization mixture. When the
polymerization mixture reaches the polymerization temperature, the remainder
of the peroxide can be added to the mixture to control the further
polymerization rate. Preferably, the addition is continuous, since this allows the
most accurate control of the polymerization rate and a constant polymerization
30 heat output, ensuring the highest efficiency and polystyrene quality. The
addition time of 2-4 hours allows a very efficient use of the initiator. By using
such addition times, high yields of high-quality polystyrene were attained.
In another preferred embodiment, the reaction mixture is formulated at or near
35 the polymerization temperature. In this process, hereinafter called warm-start
process, it is not necessary to add a certain amount of peroxide at the start
6
while the remainder is dosed over time. However, also in this warm-start
process it can be beneficial to add up to 40 % w/w of all peroxide immediately
after formation of the reaction mixture, the remainder being added over time.
Also in this warm-start process preferably at least 10 % w/w of all peroxide is
present from the moment the reaction mixture reaches the desired reactio5 n
(polymerization) temperature. If this procedure is used, the peroxide according
to the invention preferably is added as the last ingredient. This procedure is
particularly preferred if a certain amount of polymerization inhibitor (a radical
trapping species) is present in the reaction mixture. If such a radical scavenger
10 is present, for instance because it is introduced with the monomer wherein it is
typically used as a stabilizer, the initially dosed peroxide will react with said
scavenger, thus preventing a delayed start of the polymerization reaction.
The organic peroxide initiator of formula (I) is used in a first step i)of the
15 process of the invention, during which said organic peroxide initiator is heated
at a polymerization temperature ranging from 100°C to 120°C. In an
embodiment of the invention, this temperature ranges from 105°C to 115°C,
preferably is 110°C. Such a temperature is close to the one hour half life
temperature of the organic peroxides of formula (I), as measured according to
20 the well-known technique of measuring the rate of initiator decomposition in the
aromatic solvent cumene. Indeed, in a preferred embodiment of the invention,
the organic peroxides of formula (I) are used as first stage initiators.
During the step i) a), the aqueous suspension is heated, at a polymerization
25 temperature ranging from 100°C to 120°C, preferably 105°C to 115°C, and
more preferably of 110°C for a time sufficient to effect at least partial
decomposition of said initiator and initiate polymerization of the styrene
monomer. This time may range from about 1,5 hours to about 3 hours.
30 It is to be understood that the words "continuous addition" is used to describe
the step of adding peroxide to the polymerizing reaction mixture at
polymerization conditions.
The addition can be done intermittently during the polymerization over a period
35 of time wherein preferably at least 20%, preferably at least 40%, more
preferably at least 60%, of all monomer used in the process is polymerized,
7
meaning that at least two portions of initiator are added to the reaction mixture,
or it can be continuous, meaning that for a certain period of time the initiator is
continuously added to the reaction mixture, or any combination of these
techniques. Examples of a combination of such techniques include, for
instance, a process wherein the initiator is first added continuously, then th5 e
addition is stopped, and then again it is added continuously. If an intermittent
operation is selected, there are at least 2, preferably at least 4, more preferably
at least 10, and most preferably at least 20 moments at the polymerization
temperature at which the initiator is added.
10
Most preferably, the peroxide is added continuously and/or intermittently from
the start of the polymerization reaction, preferably after at least 5%, more
preferably at least 10%, even more preferably at least 20%, most preferably at
least 30%, of the monomer (s) has already been polymerized . During the
15 addition period at least 2, preferably at least 5, more preferably at least 10%,
more preferably at least 20%, more preferably at least 30%, and most
preferably at least 50%, of all monomer used in the process is polymerized.
The addition can be effected at any suitable entry point to the reactor.
20 In an embodiment of the invention, the aqueous suspension of step i) further
comprises at least one additional organic peroxide initiator, different from said
organic peroxide initiator of formula (I).
Preferably, said additional organic peroxide initiator plays the role
of the second stage initiator. When the aqueous suspension of step i)comprises
25 an organic peroxide initiator of formula (I) as first stage initiator and at least one
additional other organic peroxide initiator as second stage initiator, step
i)comprises a stage i) b’), during which said suspension is heated at a
temperature ranging from 100°C to 120°C, preferably from 105°C to 115°C,
and more preferably to 110°C, and a second stage i) c’) during which said
30 suspension is heated at a temperature corresponding to the one hour half life
temperature of the at least additional other organic peroxide.
Said additional peroxide initiator may be selected among any
organic peroxide initiator different from formula (I) and having a one hour half
life temperature, as measured according to the well-known technique of
35 measuring the rate of initiator decomposition in the aromatic solvent cumene,
above 110°C. In an embodiment of the invention, the additional peroxide
8
initiator is selected from the group consisting of compounds having the formula
(II), ie OO-t-alkyl-O-alkyl monoperoxycarbonate, wherein t-alkyl contains from 4
to 12 carbon atoms, preferably from 4 to 5 carbon atoms, and alkyl contains
from 3 to 12 carbon atoms, and preferably 8 carbon atoms, and their mixtures.
In an embodiment of the process of the invention, the at leas5 t
additional peroxide initiator is OO-t-amyl-O-2-ethylhexyl monoperoxycarbonate
(also referred to hereinafter as TAEC).
In another embodiment of the process of the invention, the at least
additional peroxide initiator is OO-t-butyl-O-2-ethylhexyl monoperoxycarbonate
10 (also referred to hereinafter as TBEC).
These products are respectively commercially available from the
company ARKEMA under the tradename “Luperox® TAEC” and “Luperox®
TBEC”.
In an embodiment of the process of the invention, in particular
15 when OO-t-amyl-O-2-ethylhexyl monoperoxycarbonate or OO-t-butyl-O-2-
ethylhexyl monoperoxycarbonate is used as the second stage initiator, the
aqueous suspension is heated, during said second stage I°)b’), at a
temperature ranging from 120°C to 140°C, preferably at a temperature of about
130°C. Said second stage may last from 1 to 3 hours.
20 In an embodiment of the process of the invention, the second stage
initiator is added continuously, as the first stage initiator.
In an embodiment of the process of the invention, said first stage
lasts about 2 to 3 hours and said second stage lasts about 2 hours.
In another embodiment of the process of the invention, the organic
25 peroxide of formula (I) plays the role of the second stage initiator and said
additional peroxide initiator plays the role of the first stage initiator.
In an embodiment of the invention, said organic peroxide initiator of
formula (I) is used in the aqueous suspension of step i) in amounts from 4 to 25
milli equivalents of initiator per liter of styrene, more preferably from 12 to 20
30 milli equivalents of initiator per liter of styrene.
Styrene is the preferred monomer for the process of the invention.
However, up to 15% of the weight of styrene may be replaced by other
ethylenically unsaturated copolymerizable monomers such as alkylstyrenes,
alpha methylstyrene, acrylic acid esters and acrilonitrile. For example, the
35 styrene monomer to be polymerized may also contain up to 15 weight %, with
9
respect to the total weight of styrene, of copolymerizable monomers other than
styrene monomers.
In an embodiment of the invention, said additional organic peroxide
initiator used in the aqueous suspension of step i) in amounts from 1 to 20 milli
equivalents of initiator per liter of styrene, more preferably from 2 to 10 mill5 i
equivalents of initiator per liter of styrene.
The process of the invention also comprises a step, step ii), of
addition of a blowing agent selected from the group consisting of alkanes
having 4 to 6 carbon atoms and mixtures thereof.
10 The blowing agent may be added to the aqueous suspension at
any time during step i), or after step i) is completed.
In an embodiment of the invention, the blowing agent is added
during step i), i.e. during the polymerization of the styrene monomer. In such a
case, when step i) comprise a first and a second stages, the blowing agent may
15 be added during the first stage of step i). For instance, the blowing agent may
be added at the end of the first stage of step i).
In another embodiment of the invention, the spherical beads of
polystyrene obtained at the end of step i) are segregated by size and the
blowing agent is added to the segregated spherical beads. This embodiment of
20 the process allows a more precise control of the bead sizes.
In an embodiment of the invention, said blowing agent is selected
from the group consisting of butane, 2-methylbutane, pentane, cyclohexane
and mixtures thereof. Such blowing agents are well known products which are
commercially available.
25 Preferably, said blowing agent is pentane.
In an embodiment of the invention, the blowing agent is added in
amounts ranging from 5 to 10 %, by weight, with respect to the weight of
styrene.
In an embodiment of the invention, an additive selected from the
30 group comprising flame retardant agents, inorganic suspension stabilizers,
such as calcium phosphate or magnesium pyrophosphate, organic suspension
stabilizers, such as polyvinylpyrrolidone, polyvinyl alcohol or
hydroxyethylcellulose, surfactants, chain transfer agents, nucleating agents,
expansion aids, lubricants, plasticizers and mixtures thereof, is added to the
35 aqueous suspension at step i) or at step ii).
10
The flame retardant agent may be selected from the group
comprising hexabromocyclododecane (HBCD), .tetrabromobisphenol A
(TBBPA), decabromodiphenyl ether (Deca – BDE), pentabromodiphenyl ether
(Penta – BDE), octabromodiphenyl ether (Octa – BDE), tris-
(dibromopropyl)phosphate, carbon tetrabromide, beta-dibromopropionate5 ,
tetrabromoethylene, 1-2-dibromo-1,1,2,2-tetrachloroethane, 1,1,2,2-
tetrabromoethane, dibromodichloroethane, 1,2-dibromo-1,1-dichloroethane,
1,2-dibromo-1,2,2-trichloroethane, 1,2,3,4-tetrabromobutane, 1,2,3-
tribromopropane, pentabromoethane, tribromotrichlorocyclohexane, 1,2,4-
10 tribromobutane, tetrabromopentane, hexabromoethane,
tetrabromodichlorocyclohexane, pentabromomonochlorocyclohexane, 1,2-di-
(dibromomethyl)benzene, alpha,beta-dibromoethylbenzene, alpha,betadibromopropionate
and mixtures thereof.
Preferably, the flame retardant agent is hexabromocyclododecane.
15
The peroxide or peroxides used in the process according to the
invention are added to the aqueous suspension at step i)in the pure form or,
preferably, in the form of a dilute solution or dispersion (such as a suspension
or emulsion in styrene). One or more suitable solvents can be used to dilute the
20 initiator., Solvents are of such a nature that it is acceptable to leave them as a
residue in the final polymer, as it is the case for solvents that are desired
plasticizers for the final resin.
Another aspect of the invention relates to an expandable
25 polystyrene obtainable by the process described above. Such an expandable
polystyrene shows a high molecular weight and is therefore useful in insulation
or packaging applications. For example, the expandable polystyrene according
to the invention may be used in the manufacture of insulation parts, for
example in the transport industry. The expandable polystyrene according to the
30 invention may also be used in the manufacture of packaging having good
mechanical properties. A further aspect of the invention relates to insulation
parts comprising an expandable polystyrene according to the invention.
Another aspect of the invention relates to packagings comprising an
expandable polystyrene according to the invention.
35 The present invention will now be further illustrated by means of the
following examples.
11
EXAMPLES :
In all examples below, the molecular weight of the product obtained
is measured according to the method given hereinabove in the description o5 f
the present application.
EXAMPLE 1: Preparation of 1-methoxy-1-t-amylperoxycyclohexane
(TAPMC)
10
A mixture of t-amyl hydroperoxide (TAHP), cyclohexanone and
methanol is treated with 70% sulfuric acid at -6 to -4C. In fifteen minutes, an
equilibrium mixture of 1-methoxy-1-t-amylperoxycyclohexane, 1,1-di-(tamylperoxy)-
cyclohexane and the unreacted starting materials cyclohexanone
15 and TAHP is formed. Small amounts (2%) of cyclohexane-1,1-
dimethyoxyketal (CDMK) are also produced in the reaction mixture. The
reaction mixture is quenched with cold water and the aqueous phase is
separated from the organic phase, which is purified by washing.
20 EXAMPLE 2 : (comparative) BPO/TAEC
Into a 2 liter pressure vessel of the Büchi type, equipped with a
double envelop and specific stirring means (3 blade stirrer on two levels) were
added at 20°C and under stirring 680 g of deionized water with 0.64 g of
25 polyvinyl alcohol (Alcotex® 72.5 available from the company HARCO). Were
further added 320 g of styrene monomer with 1.44 g of dibenzoyle peroxide
(Luperox® A75 available from the company ARKEMA), and 0.42 g of OO-tamyl
O-2-ethylhexyl monoperoxycarbonate (TAEC available under the
trademark Luperox® TAEC from the company ARKEMA). This aqueous
30 suspension was heated at 90°C for 1 hour and maintained at this temperature
for 4 hours for the first polymerization stage. In this example, dibenzoyle
peroxide is used as the first stage initiator.
After 5 hours, were further added 21.1 g of pentane in two minutes
using a high pressure pump. The reaction medium was then heated at 130°C
35 for 0,5 hour and maintained at this temperature for 2 hours. In this example,
12
OO-t-amyl O-2-ethylhexyl monoperoxycarbonate is used as second stage
initiator.
The reaction medium was then cooled down 1 hour. The obtained
polystyrene beads are collected by filtration and dried.
The obtained product has a molecular weight (Mw) of 158, 005 0
g/mol with 970 ppm of residual styrene monomer.
The overall cycle time is 8.5 hours.
EXAMPLE 3 : (comparative) TAPMC/TAEC
10
Into a 2 liter pressure vessel of the Büchi type, equipped with a
double envelop and specific stirring means (3 blade stirrer) were added at 20°C
and under stirring 680 g of deionized water with 0.64 g of polyvinyl alcohol
(Alcotex® 72.5 available from the company HARCO). Were further added 320
15 g of styrene monomer with 1.02 g of 1-methoxy-1-t-amylperoxycyclohexane
(TAPMC) as obtained in Example 1 above, and 0.42 g of OO-t-amyl O-2-
ethylhexyl monoperoxycarbonate (TAEC available under the trademark
Luperox® TAEC from the company ARKEMA). This aqueous suspension was
heated at 110°C for 1 hour and maintained at this temperature for 2.5 hours for
20 the first polymerization stage. In this example, 1-methoxy-1-tamylperoxycyclohexane
is used as first stage initiator.
After 3.5 hours, were further added 21.1 g of pentane in two
minutes using a high pressure pump. The reaction medium was then heated at
130°C for 0.5 hour and maintained at this temperature for 2 hours. In this
25 example, OO-t-amyl O-2-ethylhexyl monoperoxycarbonate is used as second
stage initiator.
The reaction medium was then cooled down during 1 hour. The
obtained polystyrene beads are collected by filtration and dried.
The obtained product has a molecular weight (Mw) of 226, 000
30 g/mol with 700 ppm of residual styrene monomer.
The overall cycle time is 7 hours.
EXAMPLE 4 : (comparative) TAPMC/TBEC
35 The same process as in Example 3 is repeated with the same
amounts and the same cycle time except that the 0.42 g of TAEC is replaced
13
by 0.42 g of OO-t-butyl O-2-ethylhexyl monoperoxycarbonate (Luperox® TBEC
available from the company ARKEMA).
In this example, 1-methoxy-1-t-amylperoxycyclohexane is used as
first stage initiator and OO-t-butyl O-2-ethylhexyl monoperoxycarbonate is used
as second stage initiator5 .
The obtained product has a molecular weight (Mw) of 220, 000
g/mol with 500 ppm of residual styrene monomer.
10 EXAMPLE 5 : (comparative) HBCD
The same process as in Example 3 is repeated with the same
amounts and the same cycle time except that 2.1 g of
hexabromocyclododecane is added at the aqueous suspension of styrene
15 monomer.
The obtained product has a molecular weight (Mw) of 153, 000
g/mol with 1600 ppm of residual styrene monomer.
EXAMPLE 6 : (Invention) TAPMC/TAEC continuous injection
20
Into a 2 liter pressure vessel of the Büchi type, equipped with a
double envelop and specific stirring means (3 blade stirrer on two levels) were
added at 20°C and under stirring 680 g of deionized water with 0.64 g of
polyvinyl alcohol (Alcotex® 72.5 available from the company HARCO). Were
25 further added 320 g of styrene monomer with 0.42 g of OO-t-amyl O-2-
ethylhexyl monoperoxycarbonate (TAEC available under the trademark
Luperox® TAEC from the company ARKEMA). This aqueous suspension was
heated at 110°C while simultaneously adding continuously at a constant
flowrate using a pressure pump a solution made up of 1,02 g of 1-methoxy-1-t30
amylperoxycyclohexane (TAPMC) and 26,2 g of styrene.Duration of the
injection is 2,5 hours for the first step of the polymerization.
After 2,5 hours, were further added 21.1 g of pentane in two
minutes using a high pressure pump. The reaction medium was then heated at
35 130°C for 0,5 hour and maintained at this temperature for 2 hours. In this
14
example, OO-t-amyl O-2-ethylhexyl monoperoxycarbonate is used as second
stage initiator.
The reaction medium was then cooled down for 1 hour. The
obtained polystyrene beads are collected by filtration and dried.
The obtained product has a molecular weight (Mw) of 206, 005 0
g/mol with 764 ppm of residual styrene monomer.
The overall cycle time is 6 hours.
EXAMPLE 7 : (Invention) TAPMC/TAEC continuous injection
10
Into a 2 liter pressure vessel of the Büchi type, equipped with a
double envelop and specific stirring means (3 blade stirrer on two levels) were
added at 20°C and under stirring 680 g of deionized water with 0.64 g of
polyvinyl alcohol (Alcotex® 72.5 available from the company HARCO). Were
15 further added 320 g of styrene monomer with 0.42 g of OO-t-amyl O-2-
ethylhexyl monoperoxycarbonate (TAEC available under the trademark
Luperox® TAEC from the company ARKEMA). This aqueous suspension was
heated at 115°C while simultaneously adding continuously at a constant
flowrate using a pressure pump a solution made up of 1,02 g of 1-methoxy-1-t20
amylperoxycyclohexane (TAPMC) and 20,8 g of styrene.Duration of the
injection is 2 hours for the first step of the polymerization.
After 2 hours, were further added 21.1 g of pentane in two minutes
using a high pressure pump. The reaction medium was then heated at 130°C
25 for 0,5 hour and maintained at this temperature for 1 hour. In this example, OOt-
amyl O-2-ethylhexyl monoperoxycarbonate is used as second stage initiator.
The reaction medium was then cooled down for 1 hour. The
obtained polystyrene beads are collected by filtration and dried.
The obtained product has a molecular weight (Mw) of 195, 000
30 g/mol with 940 ppm of residual styrene monomer.
The overall cycle time is 4,5 hours.
EXAMPLE 8 : (Invention) TAPMC/TAEC/HBCD continuous
35 injection.
15
The same process as in Example 6 is repeated with the same
amounts and the same cycle time except that 2.1 g of
hexabromocyclododecane is added at the aqueous suspension of styrene
monomer5 .
The obtained product has a molecular weight (Mw) of 193, 000
g/mol with 770 ppm of residual styrene monomer.
The overall cycle time is 6 hours.
16
We Claim:-
1. Process for the preparation of expandable polystyrene
comprising the following steps 5 :
- i) a) preparing an aqueous suspension comprising styrene
monomer
- i) b) heating the suspension at a polymerisation temperature
ranging from 100°C to 120°C,
10 - i) c) adding continuously, before, during and/or after step i) b) at
least one organic peroxide initiator of formula (I) 1-alkoxy-1-talkylperoxycyclohexane
in which the alkoxy group contains 1 to 4 carbon
atoms, the t-alkyl group contains 4 to 12 carbon atoms, and the cyclohexane
ring may optionally be substituted with 1 to 3 alkyl groups each, independently
15 having 1 to 3 carbon atoms,
- ii) adding a blowing agent selected from the group consisting of
alkanes having from 4 to 6 carbon atoms and mixtures thereof.
2. Process according to claim 1, wherein the at least one organic
peroxide initiator is 1-methoxy-1-t-amylperoxycyclohexane (TAPMC).
20 3. Process according to claim 1 or 2, wherein said blowing agent is
selected from the group consisting of butane, 2-methylbutane, pentane,
cyclohexane and mixtures thereof.
4. Process according to any of claims 1 to 3, wherein preferably at
most 40% by weight (%w/w), more preferably at most 30 to 20% by weight, and
25 most preferably at most 5% by weight of the organic peroxide, based on the
total weight of the peroxide used during the polymerization, is present before
step i) b), while the remainder is added continuously over a period of at least 1,
preferably 2, and more preferably 2-4 hours during or after step i) b).
5. Process according to any of claims 1 to 4, wherein the
30 temperature of step i) ranges from 105°C to 115°C, preferably is 110°C.
6. Process according to any of claims 1 to 5, wherein the aqueous
suspension of step i) further comprises at least one additional organic peroxide
initiator, different from said organic peroxide initiator of formula (I).
7. Process according to claim 6, wherein said additional peroxide
35 initiator is selected from the group consisting of compounds having the formula
(II), ie OO-t-alkyl-O-alkyl monoperoxycarbonate, wherein t-alkyl contains from 4
17
to 12 carbon atoms, preferably from 4 to 5 carbon atoms, and alkyl contains
from 3 to 12 carbon atoms, and preferably 8 carbon atoms, and their mixtures.
8. Process according to any of claims 1 to 7, wherein said organic
peroxide initiator of formula (I) is used in the aqueous suspension of step i)in
amounts from 4 to 25 milli equivalents of initiator per liter of styrene, mor5 e
preferably from 12 to 20 milli equivalents of initiator per liter of styrene.
9. Process according to any of claims 1 to 8, wherein the styrene
monomer to be polymerized also contains up to 15 weight %, with respect to
the total weight of styrene, of copolymerizable monomers other than styrene
monomers.
10. Process according to any of claims 1 to 19, wherein
hexabromocyclododecane is added to the aqueous suspension at step i) or at
step ii).
11. Process according to any of claims 6 to 10, wherein the
aqueous suspension of step i) comprises an organic peroxide initiator of
formula (I) as first stage initiator and at least one additional other organic
peroxide initiator as second stage initiator, step i) comprises a stage i) b’),
during which said suspension is heated at a temperature ranging from 100°C to
120°C, preferably from 105°C to 115°C, and more preferably to 110°C, and a
second stage i) c’) during which said suspension is heated at a temperature
corresponding to the one hour half life temperature of the at least additional
other organic peroxide.
12. Expandable polystyrene obtainable by a process according to
one of claims 1 to 11, wherein it shows a molecular weight (Mw) of at least 170,
000 g/mol, preferably of at least 175, 000 g/mol, and more preferably of at least
190, 000 g/mol.