U.S. patent application number 14/683238 was filed with the patent office on 2015-07-30 for process for the preparation of expandable polystyrene by continuous injection of a liquid organic peroxide.
This patent application is currently assigned to ARKEMA FRANCE. The applicant listed for this patent is ARKEMA FRANCE. Invention is credited to Jacques COCHET, Pascal NICOL.
Application Number | 20150210819 14/683238 |
Document ID | / |
Family ID | 41820421 |
Filed Date | 2015-07-30 |
United States Patent
Application |
20150210819 |
Kind Code |
A1 |
NICOL; Pascal ; et
al. |
July 30, 2015 |
PROCESS FOR THE PREPARATION OF EXPANDABLE POLYSTYRENE BY CONTINUOUS
INJECTION OF A LIQUID ORGANIC PEROXIDE
Abstract
A process for the preparation of expandable polystyrene
including the following steps: i.degree.) heating an aqueous
suspension including styrene monomer and at least one organic
peroxide initiator of formula (I)
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, at a temperature ranging from 100.degree. C. to
120.degree. C.), ii.degree.) adding a blowing agent selected from
the group of alkanes having from 4 to 6 carbon atoms and mixtures
thereof. Also, an expandable polystyrene obtainable according to
such a process and to insulation parts and packaging including such
an expandable polystyrene.
Inventors: |
NICOL; Pascal; (Saint Genis
Laval, FR) ; COCHET; Jacques; (Chanas, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ARKEMA FRANCE |
Colombes |
|
FR |
|
|
Assignee: |
ARKEMA FRANCE
Colombes
FR
|
Family ID: |
41820421 |
Appl. No.: |
14/683238 |
Filed: |
April 10, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13386958 |
Feb 17, 2012 |
9040600 |
|
|
PCT/FR2010/051548 |
Jul 22, 2010 |
|
|
|
14683238 |
|
|
|
|
61228740 |
Jul 27, 2009 |
|
|
|
Current U.S.
Class: |
521/56 |
Current CPC
Class: |
C08J 9/20 20130101; C08J
9/0023 20130101; C08J 2203/14 20130101; C08F 4/34 20130101; C08J
2325/06 20130101; C08F 4/38 20130101; C08J 9/141 20130101; C08F
2/18 20130101; C08J 2325/04 20130101; C08F 12/08 20130101; C08F
2/18 20130101 |
International
Class: |
C08J 9/20 20060101
C08J009/20; C08J 9/00 20060101 C08J009/00; C08J 9/14 20060101
C08J009/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 27, 2009 |
FR |
0955241 |
Claims
1. Process for the preparation of expandable polystyrene comprising
the following steps: I.degree.)a) preparing an aqueous suspension
comprising styrene monomer; I.degree.)b) heating the suspension at
a polymerization temperature ranging from 100.degree. C. to
120.degree. C.; I.degree.)c) adding continuously, during and/or
after step I.degree.)b) at least one organic peroxide initiator of
formula (I) 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, at most 40% by weight (% w/w) of the organic
peroxide based on the total weight of the peroxide used during the
polymerization, is present before step I.degree.)b), while the
remainder is added continuously over a period of at least 1 hour
during or after step I.degree.)b); and ii.degree.) 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-tamylperoxycyclohexane
(TAPMC).
3. Process according to claim 1, wherein said blowing agent is
selected from the group consisting of butane, 2-methylbutane,
pentane, cyclohexane and mixtures thereof.
4. Process according to claim 1, wherein the temperature of step
i.degree.) ranges from 105.degree. C. to 115.degree. C.
5. Process according to claim 1, wherein the aqueous suspension of
step i.degree.) further comprises at least one additional organic
peroxide initiator, different from said organic peroxide initiator
of formula (I).
6. Process according to claim 5, wherein said additional peroxide
initiator is of formula (II) OO-t-alkyl-O-alkyl
monoperoxycarbonate, wherein t-alkyl contains from 4 to 12 carbon
atoms and alkyl contains from 3 to 12 carbon atoms and their
mixtures.
7. Process according to claim 1, wherein said organic peroxide
initiator of formula (I) is used in the aqueous suspension of step
i.degree.) in amounts from 4 to 25 milli equivalents of initiator
per liter of styrene.
8. Process according to claim 1, 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.
9. Process according to claim 1, wherein hexabromocyclododecane is
added to the aqueous suspension at step i.degree.) or at step
ii.degree.).
10. Process according to claim 5, wherein the aqueous suspension of
step i.degree.) comprises the organic peroxide initiator of formula
(I) as a first stage initiator and the at least one additional
other organic peroxide initiator different from said organic
peroxide initiator of formula (I) as a second stage initiator, step
i.degree.) comprises a stage I.degree.)b'), during which said
suspension is heated at the temperature ranging from 100.degree. C.
to 120.degree. C., and a second stage I.degree.)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 different from said organic peroxide initiator of formula
(I).
11. Process according to claim 1, wherein 20 to 30% by weight of
the organic peroxide is added continuously during step
--I.degree.)c)--.
12. Process according to claim 1, wherein, at most, 5% by weight of
the organic peroxide is added continuously during step
--I.degree.)c)--.
13. Process according to claim 1, wherein the organic peroxide is
added continuously over a period of at least 2 hours.
14. Process according to claim 1, wherein the organic peroxide is
added continuously over a period of 2-4 hours.
15. Process according to claim 4, wherein the wherein the
temperature of step i.degree.) is 110.degree. C.
16. Process according to claim 6, wherein the t-alkyl contains from
4-5 carbon atoms and the alkyl contains 8 carbon atoms.
17. Process according to claim 7, wherein the organic peroxide
initiator of formula (I) is used in the aqueous suspension of step
i.degree.) in amounts from 12 to 20 milli equivalents of initiator
per liter of styrene.
18. Process according to claim 10, wherein the suspension is heated
at a temperature ranging from 105.degree. C. to 115.degree. C.
19. Process according to claim 10, wherein the suspension is heated
to a temperature of 110.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional application of U.S.
application Ser. No. 13/386,958, filed on Feb. 17, 2012, which is a
national stage application of International application No.
PCT/FR2010/051548, filed on Jul. 22, 2010, which claims priority of
French application no. 0955241, filed on Jul. 27, 2009, and U.S.
provisional application No. 61/228,740, filed on Jul. 27, 2009.
Each of U.S. application Ser. No. 13/386,958, International
application no. PCT/FR2010/051548, French application no. 0955241,
and U.S. provisional application No. 61/228,740 are hereby
incorporated by reference in entirety.
TECHNICAL FIELD
[0002] The present invention relates to a process for the
preparation of expandable polystyrene and to an expandable
polystyrene obtainable by such a process.
BACKGROUND
[0003] 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 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 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.
[0004] Traditionally, suspension polymerization to prepare EPS is
conducted in a process using two different temperature stages and
two 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.degree. C. to
95.degree. C. Other first stage initiators useful in this
temperature range might include tertiary butyl
peroxy-2-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.degree. C. to 135.degree. C. The second stage is usually a
finishing step intended to minimize residual monomer in the EPS. In
commercial processing, this stage is often held above 125.degree.
C. for prolonged intervals to reduce monomer content to acceptable
levels.
[0005] 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.
[0006] In view of alleviating this drawback, document U.S. Pat. No.
6,608,150 has proposed an improved process for the preparation of
expandable polystyrene in which "intermediate" temperature
peroxides, that is to say initiator peroxides having a one hour
half-life temperature ranging from 101.degree. C. to 111.degree.
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
hours.
[0007] Expandable polystyrene, as prepared in the suspension
process, is in the form of essentially spherical beads. It is
mentioned in U.S. Pat. No. 6,608,150 that some blowing agent, such
as pentane, may be used in the process in order to render the
polystyrene beads expandable.
[0008] 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).
[0009] Additionally, it is more and more requested in the industry
that the 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.
[0010] It appears then that several factors may lead, in the
preparation process of expandable polystyrene, to a significant
decrease of the molecular weight of such expandable
polystyrene.
BRIEF SUMMARY OF THE DISCLOSURE
[0011] 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 Chromatography) method using Polystyrene
standards.
[0012] It is important that the expandable polystyrene has a high
molecular weight in order to guarantee the mechanical properties of
the final materials.
[0013] The Applicant has now discovered that by using a specific
initiator peroxide, it was possible to accelerate the preparation
of expandable polystyrene while using a blowing agent and to still
obtain polystyrene having a particularly high molecular weight.
[0014] 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.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0015] A first aspect of the invention relates to a process for the
preparation of expandable polystyrene comprising the following
steps:
[0016] I.degree.)a) preparing an aqueous suspension comprising
styrene monomer
[0017] I.degree.)b) heating the suspension at a polymerization
temperature ranging from 100.degree. C. to 120.degree. C.,
[0018] I.degree.)c) adding continuously, before, during and/or
after step I.degree.)b) at least one organic peroxide initiator of
formula (I) 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,
[0019] ii.degree.) adding a blowing agent selected from the group
consisting of alkanes having from 4 to 6 carbon atoms and mixtures
thereof.
[0020] The process according to the invention allows obtaining
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.
[0021] Because of its high molecular weight, the expandable
polystyrene according to the invention may be used efficiently in
insulation or packaging applications.
[0022] Moreover, the process of the invention has a conversion time
reduced compared to the ones of the prior art.
[0023] The process of the invention uses at least one organic
peroxide initiator of formula (I), i.e.
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.
[0024] According to the present invention, it has been found that
the use of 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 (I) but having a chemical formula different than formula
(I).
[0025] As organic peroxides of formula (I) one can cite
1-alkoxy-1-t-amylperoxycyclohexane 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 atoms.
[0026] In an embodiment of the invention, the at least one organic
peroxide initiator is 1-methoxy-1-t-amylperoxycyclohexane (also
referred hereinafter as TAPMC).
[0027] 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 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.degree.)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.degree.)b), depending on the polymerization time. More
preferably, the remainder of the peroxide is added from the time
the reaction mixture temperature is controlled at the desired
reaction temperature.
[0028] 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) 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 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.
[0029] In another preferred embodiment, the reaction mixture is
formulated at or near 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 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 reaction (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 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.
[0030] The organic peroxide initiator of formula (I) is used in a
first step i.degree.) of the process of the invention, during which
said organic peroxide initiator is heated at a polymerization
temperature ranging from 100.degree. C. to 120.degree. C. In an
embodiment of the invention, this temperature ranges from
105.degree. C. to 115.degree. C., preferably is 110.degree. C. Such
a temperature is close to the one hour half-life temperature of the
organic peroxides of formula (I), as measured according to 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.
[0031] During the step I.degree.)a), the aqueous suspension is
heated, at a polymerization temperature ranging from 100.degree. C.
to 120.degree. C., preferably 105.degree. C. to 115.degree. C., and
more preferably of 110.degree. 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.
[0032] 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.
[0033] The addition can be done intermittently during the
polymerization over a period 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, 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 the 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.
[0034] 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 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.
[0035] In an embodiment of the invention, the aqueous suspension of
step i.degree.) further comprises at least one additional organic
peroxide initiator, different from said organic peroxide initiator
of formula (I).
[0036] Preferably, said additional organic peroxide initiator plays
the role of the second stage initiator. When the aqueous suspension
of step i.degree.) 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.degree.) comprises a stage I.degree.)b'), during which said
suspension is heated at a temperature ranging from 100.degree. C.
to 120.degree. C., preferably from 105.degree. C. to 115.degree.
C., and more preferably to 110.degree. C., and a second stage
I.degree.)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.
[0037] 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 measuring the rate of initiator
decomposition in the aromatic solvent cumene, above 110.degree. C.
In an embodiment of the invention, the additional peroxide
initiator is selected from the group consisting of compounds having
the formula (II), i.e. 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.
[0038] In an embodiment of the process of the invention, the at
least additional peroxide initiator is OO-t-amyl-O-2-ethylhexyl
monoperoxycarbonate (also referred to hereinafter as TAEC).
[0039] In another embodiment of the process of the invention, the
at least additional peroxide initiator is OO-t-butyl-O-2-ethylhexyl
monoperoxycarbonate (also referred to hereinafter as TBEC).
[0040] These products are respectively commercially available from
the company ARKEMA under the trade name "Luperox.RTM. TAEC" and
"Luperox.RTM. TBEC".
[0041] In an embodiment of the process of the invention, in
particular 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.degree.)b'), at a temperature ranging from
120.degree. C. to 140.degree. C., preferably at a temperature of
about 130.degree. C. Said second stage may last from 1 to 3
hours.
[0042] In an embodiment of the process of the invention, the second
stage initiator is added continuously, as the first stage
initiator.
[0043] 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.
[0044] In another embodiment of the process of the invention, the
organic 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.
[0045] In an embodiment of the invention, said organic peroxide
initiator of formula (I) is used in the aqueous suspension of step
i.degree.) in amounts from 4 to 25 milli equivalents of initiator
per liter of styrene, more preferably from 12 to 20 milli
equivalents of initiator per liter of styrene.
[0046] 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 styrene monomer to be
polymerized may also contain up to 15 weight %, with respect to the
total weight of styrene, of copolymerizable monomers other than
styrene monomers.
[0047] In an embodiment of the invention, said additional organic
peroxide initiator used in the aqueous suspension of step
i.degree.) in amounts from 1 to 20 milli equivalents of initiator
per liter of styrene, more preferably from 2 to 10 milli
equivalents of initiator per liter of styrene.
[0048] The process of the invention also comprises a step, step
ii.degree.), of addition of a blowing agent selected from the group
consisting of alkanes having 4 to 6 carbon atoms and mixtures
thereof.
[0049] The blowing agent may be added to the aqueous suspension at
any time during step i.degree.), or after step i.degree.) is
completed.
[0050] In an embodiment of the invention, the blowing agent is
added during step i.degree.), i.e. during the polymerization of the
styrene monomer. In such a case, when step i.degree.) comprise a
first and a second stages, the blowing agent may be added during
the first stage of step i.degree.). For instance, the blowing agent
may be added at the end of the first stage of step i.degree.).
[0051] In another embodiment of the invention, the spherical beads
of polystyrene obtained at the end of step i.degree.) are
segregated by size and the blowing agent is added to the segregated
spherical beads. This embodiment of the process allows a more
precise control of the bead sizes.
[0052] 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.
[0053] 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.
[0054] In an embodiment of the invention, an additive selected from
the 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 aqueous
suspension at step i.degree.) or at step ii.degree.).
[0055] 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-dibromopropionate, 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-tribromobutane,
tetrabromopentane, hexabromoethane, tetrabromodichlorocyclohexane,
pentabromomonochlorocyclohexane, 1,2-di-(dibromomethyl)benzene,
alpha,beta-dibromoethylbenzene, alpha,beta-dibromopropionate and
mixtures thereof.
[0056] Preferably, the flame retardant agent is
hexabromocyclododecane. The peroxide or peroxides used in the
process according to the invention are added to the aqueous
suspension at step i.degree.) 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 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.
[0057] Another aspect of the invention relates to an expandable
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
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 packaging comprising an expandable polystyrene according to the
invention.
[0058] The present invention will now be further illustrated by
means of the following examples.
EXAMPLES
[0059] In all examples below, the molecular weight of the product
obtained is measured according to the method given hereinabove in
the description of the present application.
Example 1
[0060] Preparation of 1-methoxy-1-t-amylperoxycyclohexane
(TAPMC)
[0061] A mixture of t-amyl hydroperoxide (TAHP), cyclohexanone and
methanol is treated with 70% sulfuric acid at -6.degree. to
-4.degree. C. In fifteen minutes, an equilibrium mixture of
1-methoxy-1-t-amylperoxycyclohexane,
1,1-di-(t-amylperoxy)-cyclohexane and the unreacted starting
materials cyclohexanone and TAHP is formed. Small amounts
(.apprxeq.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.
Example 2
(Comparative) BPO/TAEC
[0062] Into a 2 liter pressure vessel of the Buchi type, equipped
with a double envelop and specific stirring means (3 blade stirrer
on two levels) were added at 20.degree. C. and under stirring 680 g
of deionized water with 0.64 g of polyvinyl alcohol (Alcotex.RTM.
72.5 available from the company HARCO). Were further added 320 g of
styrene monomer with 1.44 g of dibenzoyle peroxide (Luperox.RTM.
A75 available from the company ARKEMA), and 0.42 g of 00-t-amyl
0-2-ethylhexyl monoperoxycarbonate (TAEC available under the
trademark Luperox.RTM. TAEC from the company ARKEMA). This aqueous
suspension was heated at 90.degree. 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.
[0063] 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.degree. C. for 0.5 hour and maintained at this
temperature for 2 hours. In this example, OO-t-amyl O-2-ethylhexyl
monoperoxycarbonate is used as second stage initiator.
[0064] The reaction medium was then cooled down 1 hour. The
obtained polystyrene beads are collected by filtration and
dried.
[0065] The obtained product has a molecular weight (Mw) of 158,000
g/mol with 970 ppm of residual styrene monomer.
[0066] The overall cycle time is 8.5 hours.
Example 3
(Comparative) TAPMC/TAEC
[0067] Into a 2 liter pressure vessel of the Buchi type, equipped
with a double envelop and specific stirring means (3 blade stirrer)
were added at 20.degree. C. and under stirring 680 g of deionized
water with 0.64 g of polyvinyl alcohol (Alcotex.RTM. 72.5 available
from the company HARCO). Were further added 320 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.RTM. TAEC from the company ARKEMA). This aqueous
suspension was heated at 110.degree. C. for 1 hour and maintained
at this temperature for 2.5 hours for the first polymerization
stage. In this example, 1-methoxy-1-t-amylperoxycyclohexane is used
as first stage initiator.
[0068] 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.degree. C. for 0.5 hour and maintained at this
temperature for 2 hours. In this example, OO-t-amyl O-2-ethylhexyl
monoperoxycarbonate is used as second stage initiator.
[0069] The reaction medium was then cooled down during 1 hour. The
obtained polystyrene beads are collected by filtration and
dried.
[0070] The obtained product has a molecular weight (Mw) of 226,000
g/mol with 700 ppm of residual styrene monomer.
[0071] The overall cycle time is 7 hours.
Example 4
(Comparative) TAPMC/TBEC
[0072] 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 by 0.42 g of OO-t-butyl O-2-ethylhexyl monoperoxycarbonate
(Luperox.RTM. TBEC available from the company ARKEMA).
[0073] 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 initiator.
[0074] The obtained product has a molecular weight (Mw) of 220,000
g/mol with 500 ppm of residual styrene monomer.
Example 5
(Comparative) HBCD
[0075] 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 monomer.
[0076] 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
[0077] Into a 2 liter pressure vessel of the Buchi type, equipped
with a double envelop and specific stirring means (3 blade stirrer
on two levels) were added at 20.degree. C. and under stirring 680 g
of deionized water with 0.64 g of polyvinyl alcohol (Alcotex.RTM.
72.5 available from the company HARCO). Were 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.RTM. TAEC from the company ARKEMA). This aqueous suspension
was heated at 110.degree. C. while simultaneously adding
continuously at a constant flow rate using a pressure pump a
solution made up of 1.02 g of 1-methoxy-1-t-amylperoxycyclohexane
(TAPMC) and 26.2 g of styrene. Duration of the injection is 2.5
hours for the first step of the polymerization.
[0078] 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 130.degree. C. for 0.5 hour and maintained at this
temperature for 2 hours. In this example, OO-t-amyl O-2-ethylhexyl
monoperoxycarbonate is used as second stage initiator.
[0079] The reaction medium was then cooled down for 1 hour. The
obtained polystyrene beads are collected by filtration and
dried.
[0080] The obtained product has a molecular weight (Mw) of 206,000
g/mol with 764 ppm of residual styrene monomer.
[0081] The overall cycle time is 6 hours.
Example 7
(Invention) TAPMC/TAEC Continuous Injection
[0082] Into a 2 liter pressure vessel of the Buchi type, equipped
with a double envelop and specific stirring means (3 blade stirrer
on two levels) were added at 20.degree. C. and under stirring 680 g
of deionized water with 0.64 g of polyvinyl alcohol (Alcotex.RTM.
72.5 available from the company HARCO). Were 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.RTM. TAEC from the company ARKEMA). This aqueous suspension
was heated at 115.degree. C. while simultaneously adding
continuously at a constant flow rate using a pressure pump a
solution made up of 1.02 g of 1-methoxy-1-t-amylperoxycyclohexane
(TAPMC) and 20.8 g of styrene. Duration of the injection is 2 hours
for the first step of the polymerization.
[0083] 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.degree. C. for 0.5 hour and maintained at this
temperature for 1 hour. In this example, OO-t-amyl O-2-ethylhexyl
monoperoxycarbonate is used as second stage initiator.
[0084] The reaction medium was then cooled down for 1 hour. The
obtained polystyrene beads are collected by filtration and
dried.
[0085] The obtained product has a molecular weight (Mw) of 195,000
g/mol with 940 ppm of residual styrene monomer.
[0086] The overall cycle time is 4.5 hours.
Example 8
[0087] (Invention) TAPMC/TAEC/HBCD continuous Injection
[0088] 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 monomer.
[0089] The obtained product has a molecular weight (Mw) of 193,000
g/mol with 770 ppm of residual styrene monomer.
[0090] The overall cycle time is 6 hours.
* * * * *