U.S. patent application number 09/737270 was filed with the patent office on 2001-07-26 for process for preparing monodisperse crosslinked bead polymers.
Invention is credited to Feistel, Lothar, Halle, Olaf, Mitschker, Alfred, Podszun, Wolfgang, Schmid, Claudia.
Application Number | 20010009928 09/737270 |
Document ID | / |
Family ID | 26005363 |
Filed Date | 2001-07-26 |
United States Patent
Application |
20010009928 |
Kind Code |
A1 |
Podszun, Wolfgang ; et
al. |
July 26, 2001 |
Process for preparing monodisperse crosslinked bead polymers
Abstract
The invention relates to a process for preparing substantially
monodisperse crosslinked bead polymers useful as precursors for ion
exchangers.
Inventors: |
Podszun, Wolfgang; (Koln,
DE) ; Feistel, Lothar; (Delitzsch, DE) ;
Halle, Olaf; (Koln, DE) ; Schmid, Claudia;
(Leverkusen, DE) ; Mitschker, Alfred; (Odenthal,
DE) |
Correspondence
Address: |
BAYER CORPORATION
PATENT DEPARTMENT
100 BAYER ROAD
PITTSBURGH
PA
15205
US
|
Family ID: |
26005363 |
Appl. No.: |
09/737270 |
Filed: |
December 14, 2000 |
Current U.S.
Class: |
521/25 ; 521/33;
526/336; 526/87 |
Current CPC
Class: |
C08F 257/02
20130101 |
Class at
Publication: |
521/25 ; 521/33;
526/87; 526/336 |
International
Class: |
C08F 002/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 1999 |
DE |
19962864.5 |
Apr 18, 2000 |
DE |
10019144.4 |
Claims
What is claimed is:
1. A process for preparing monodisperse crosslinked bead polymers
comprising (a) preparing monodisperse monomer droplets in aqueous
suspension from a monomer mixture 1 comprising styrene,
divinylbenzene, and a free-radical generator, (b)
microencapsulating the resultant monomer droplets, (c) polymerizing
the microencapsulated monomer droplets to a conversion of from 10
to 75%, (d) adding a monomer mixture 2 comprising styrene and
divinyl-benzene at a temperature at which the free-radical
generator from monomer mixture 1 is active, whereupon the monomer
mixture penetrates into the microencapsulated monomer droplets that
have begun to polymerize, and (e) completing the polymerization of
the monomer mixtures.
2. A process according to claim 1 wherein monomer mixture 2 or a
portion thereof is added in the form of an emulsion in water.
3. A process according to claim 1 wherein monomer mixture 2 also
comprises acrylonitrile and/or a free-radical generator and at
least one free-radical generator from monomer mixture 1 or monomer
mixture 2 is active in step (d).
4. A process for preparing monodisperse crosslinked bead polymers
comprising (a) producing monodisperse monomer droplets in aqueous
suspension from a monomer mixture 1 comprising from 87.5 to 99.7%
by weight of styrene, from 0.2 to 10% by weight of divinylbenzene,
and from 0.1 to 2.5% by weight of a free-radical generator, (b)
microencapsulating the resultant monomer droplets, (c) polymerizing
the microencapsulated monomer droplets to a conversion of from 10
to 75%, (d) adding a monomer mixture 2 comprising from 80 to 99% by
weight of styrene, from 1 to 12% by weight of divinylbenzene, from
0 to 8% by weight of acrylonitrile, and, optionally, a free-radical
generator at a temperature at which at least one of the
free-radical generators from monomer mixture 1 or monomer mixture 2
is active, where-upon the monomer mixture penetrates into the
microencapsulated monomer droplets that have begun to polymerize,
and (e) completing the polymerization of the monomer mixtures.
5. A process according to claim 1 wherein the free-radical
generator is one or more azo compounds and/or peroxo compounds.
6. A process according to claim 4 wherein the free-radical
generator is one or more azo compounds and/or peroxo compounds.
7. A process according to claim 1 wherein step (a) is carried out
using a spraying technique involving vibrational excitation.
8. A process according to claim 4 wherein step (a) is carried out
using a spraying technique involving vibrational excitation.
9. A process according to claim 1 wherein the monomer droplets from
step (a) are microencapsulated in step (b) with a polyester, a
naturally occurring or synthetic polyamide, a polyurethane, or a
polyurea.
10. A process according to claim 4 wherein the monomer droplets
from step (a) are microencapsulated in step (b) with a polyester, a
naturally occurring or synthetic polyamide, a polyurethane, or a
polyurea.
11. A process according to claim 1 wherein polymerization step (c)
is carried out in aqueous suspension at an elevated temperature of
from 55 to 95.degree. C.
12. A process according to claim 4 wherein polymerization step (c)
is carried out in aqueous suspension at an elevated temperature of
from 55 to 95.degree. C.
13. A monodisperse, crosslinked bead polymer prepared by a process
according to claim 1.
14. A monodisperse, crosslinked bead polymer prepared by a process
according to claim 4.
15. A method comprising converting a monodisperse, crosslinked bead
polymer according to claim 13 to a cation- or anion-exchanger.
16. A method comprising converting a monodisperse, crosslinked bead
polymer according to claim 14 to a cation- or anion-exchanger.
17. A cation exchanger prepared by sulfonating bead polymers
according to claim 13.
18. A cation exchanger prepared by sulfonating bead polymers
according to claim 14.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to a process for preparing
substantially monodisperse crosslinked bead polymers useful as
precursors for ion exchangers.
[0002] In recent times increasing importance has been placed on ion
exchangers with very uniform particle size (hereinafter termed
"mono-disperse"), since the more advantageous hydrodynamic
properties of an exchanger bed made of monodisperse ion exchangers
can provide cost advantages in many applications. Monodisperse ion
exchangers can be obtained by functionalizing monodisperse
crosslinked bead polymers.
[0003] One way of preparing monodisperse crosslinked bead polymers
is known as the seed/feed process. In this process, monodisperse
polymer particles ("seed") are swollen in the monomer, which is
then polymerized. These seed/feed processes are described in EP
98,130 B1 and EP 101,943 B1, for example. EP-A 826,704 and DE-A
19,852,667 disclose seed/feed processes using microencapsulated
polymer particles as seed. Compared with conventional, directly
synthesized bead polymers, the bead polymers obtained by the
processes described above have an increased content of
uncrosslinked soluble polymer. This content of uncrosslinked
soluble polymer is undesirable during the conversion to ion
exchangers, since the polymer fractions dissolved out can become
concentrated in the reaction solutions used for the
functionalization. In addition, the relatively large amounts of
soluble polymer can cause undesirable leaching of the ion
exchangers.
[0004] U.S. Pat. No. 5,068,255 describes a seed/feed process in
which a first monomer mixture is polymerized to a conversion of
from 10 to 80% and is then mixed with a second monomer mixture
essentially free from free-radical initiator as feed under
polymerizing conditions. However, this process cannot prepare
monodisperse particles.
[0005] The object of the present invention is to provide
monodisperse crosslinked bead polymers with a low content of
soluble polymer. It has now been found that monodisperse
crosslinked bead polymers with a low content of soluble polymer can
be obtained by a seed-feed process in which the seed used comprises
incompletely polymerized, monodisperse microencapsulated monomer
droplets.
SUMMARY OF THE INVENTION
[0006] The present invention relates to a process for preparing
mono-disperse crosslinked bead polymers as precursors for ion
exchangers comprising
[0007] (a) preparing monodisperse monomer droplets in aqueous
suspension from a monomer mixture 1 comprising styrene,
divinylbenzene, and a free-radical generator,
[0008] (b) microencapsulating the resultant monomer droplets,
[0009] (c) polymerizing the microencapsulated monomer droplets to a
conversion of from 10 to 75%,
[0010] (d) adding a monomer mixture 2 comprising styrene and
divinyl-benzene at a temperature at which the free-radical
generator from monomer mixture 1 is active, whereupon the monomer
mixture penetrates into the microencapsulated monomer droplets that
have begun to polymerize, and
[0011] (e) completing the polymerization of the monomer
mixtures.
[0012] One preferred embodiment of the present invention relates to
a process in which monomer mixture 2 also comprises acrylonitrile
and/or a free-radical generator and in which at least one of the
free-radical generators from monomer mixture 1 or 2 is active in
step (d).
[0013] One particular embodiment of the present invention relates
to a process for preparing monodisperse crosslinked bead polymers
as precursors for ion exchangers comprising
[0014] (a) producing monodisperse monomer droplets in aqueous
suspension from a monomer mixture 1 comprising from 87.5 to 99.7%
by weight of styrene, from 0.2 to 10% by weight of divinylbenzene,
and from 0.1 to 2.5% by weight of a free-radical generator,
[0015] (b) microencapsulating the resultant monomer droplets,
[0016] (c) polymerizing the microencapsulated monomer droplets to a
conversion of from 10 to 75%,
[0017] (d) adding a monomer mixture 2 comprising from 80 to 99% by
weight of styrene, from 1 to 12% by weight of divinylbenzene, from
0 to 8% by weight of acrylonitrile, and, optionally, a free-radical
generator at a temperature at which at least one of the
free-radical generators from monomer mixture 1 or monomer mixture 2
is active, where-upon the monomer mixture penetrates into the
microencapsulated monomer droplets that have begun to polymerize,
and
[0018] (e) completing the polymerization of the monomer
mixtures.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The monomer mixture 1 preferably comprises from 89.5 to
99.4% by weight of styrene, from 0.5 to 8% by weight of
divinylbenzene, and from 0.1 to 2.5% by weight of free-radical
generator, particularly preferably from 92.5 to 98.7% by weight of
styrene, from 1 to 6% by weight of divinyl-benzene, and from 0.3 to
1.5% by weight of free-radical generator. The percentages given for
divinylbenzene are based on pure divinylbenzene. It is, of course,
also possible to use commercial qualities of divinylbenzene which
contain ethylvinylbenzene in addition to isomers of
divinylbenzene.
[0020] Free-radical generators that may be used are conventional
initiators such as azo compounds and/or peroxo compounds, for
example:
[0021] dibenzoyl peroxide
[0022] dilauroyl peroxide
[0023] bis(p-chlorobenzoyl) peroxide
[0024] dicyclohexyl percarbonate
[0025] 2,2'-azobisisobutyronitrile
[0026] 2,2'-azobis(2-methylbutyronitrile)
[0027] Preferred free-radical generators are aliphatic peroxy
esters corresponding to the formulas (I), (II), or (III): 1
[0028] wherein
[0029] R.sup.1 represents an alkyl radical having from 2 to 20
carbon atoms or a cycloalkyl radical having up to 20 carbon
atoms,
[0030] R.sup.2 represents a branched alkyl radical having from 4 to
12 carbon atoms, and
[0031] L represents an alkylene radical having from 2 to 20 carbon
atoms or a cycloalkylene radical having up to 20 carbon atoms.
[0032] Examples of aliphatic peroxy esters according to formula (I)
are tert-butyl peroxyacetate, tert-butyl peroxyisobutyrate,
tert-butyl peroxypivalate, tert-butyl peroxyoctoate, tert-butyl
peroxy-2-ethylhexanoate, tert-butyl peroxyneodecanoate, tert-amyl
peroxyneodecanoate, tert-amyl peroxy-pivalate, tert-amyl
peroxyoctoate, and tert-amyl peroxy-2-ethylhexanoate.
[0033] Examples of aliphatic peroxy esters according to formula
(II) are 2,5-bis(2-ethylhexanoylperoxy)-2,5-dimethylhexane,
2,5-dipivaloyl-2,5-dimethylhexane, and
2,5-bis(2-neodecanoylperoxy)-2,5-d- imethylhexane.
[0034] Examples of aliphatic peroxyesters according to formula
(III) are di-tert-butyl peroxyazelate and di-tert-amyl
peroxyazelate.
[0035] It can be advantageous to use mixtures of different
initiators, in particular mixtures of initiators with different
half-lives.
[0036] The conversion of the monomer mixture 1 into monodisperse
monomer droplets in step (a) takes place by way of known spraying
techniques, by which means the monomer mixture is dispersed in
water. Particularly suitable spraying techniques are those that are
combined with vibrational excitation. A process of this type is
described in detail in EP-A 173,518 and U.S. Pat. No. 3,922,255,
for example. The ratio of monomer mixture to water is generally
from 1:1 to 1:10, preferably from 1:1.5 to 1:5.
[0037] The particle sizes for the monomer droplets are from 10 to
500 .mu.m, preferably from 20 to 400 .mu.m, particularly preferably
from 100 to 300 .mu.m. Conventional methods, such as image
analysis, are suitable for determining the average particle size
and the particle size distribution. The ratio between the 90% value
(.O slashed. (90)) and the 10% value (.O slashed. (10)) for the
volume distribution gives a measure of the breadth of the particle
size distribution of the novel bead polymers. The 90% value (.O
slashed. (90)) is the diameter that exceeds that of 90% of the
particles. Correspondingly, the 10% (.O slashed. (10)) diameter
value exceeds that of 10% of the particles. For the purposes of the
present invention, monodisperse particle size distributions have .O
slashed. (90)/.O slashed. (10).ltoreq.1.5, preferably .O slashed.
(90)/.O slashed. (10).ltoreq.1.25.
[0038] Possible materials for the microencapsulation in step (b)
are those known for this purpose, particularly polyesters,
naturally occurring or synthetic polyamides, polyurethanes, or
polyureas. A particularly suitable naturally occurring polyamide is
gelatin, used in particular as coacervate or complex coacervate.
For the purposes of the present invention, gelatin-containing
complex coacervates are especially combinations of gelatin with
synthetic polyelectrolytes. Suitable synthetic polyelectrolytes are
copolymers incorporating units of, for example, maleic acid,
acrylic acid, methacrylic acid, acrylamide, or methacrylamide.
Gelatin-containing capsules may be hardened by conventional
hardeners, such as formaldehyde or glutaric dialdehyde. The
encapsulation of monomer droplets, for example, by gelatin, by
gelatin-containing coacervates, or by gelatin-containing complex
coacervates, is described in detail in EP 46,535 B1. The methods
for encapsulation by synthetic polymers are known. An example of a
highly suitable method is interfacial condensation, in which a
reactive component dissolved in the monomer droplet (for example,
an isocyanate or an acid chloride) reacts with a second reactive
component dissolved in the aqueous phase (for example, an amine).
Microencapsulation by gelatin-containing complex coacervate is
preferred.
[0039] The polymerization of the microencapsulated droplets from
monomer mixture 1 in step (c) takes place in aqueous suspension at
an elevated temperature of, for example, from 55 to 95.degree. C.
(preferably from 60 to 80.degree. C.) to a conversion of from 10 to
75% by weight (preferably from 15 to 50% by weight). The ideal
polymerization temperature in each case can be calculated by the
skilled worker from the half-lives for the free-radical generators.
One way of determining the conversion is IR detection of the
nonpolymerized double bonds. The suspension is stirred during the
polymerization. The stir speed here is not critical. It is possible
to use low stirring speeds which are just adequate to maintain the
droplets in suspension.
[0040] The ratio of monomer mixture 1 to water may correspond to
the ratio described under step (a), or may be changed by
concentration or dilution. The ratio used of monomer mixture 1 to
water is preferably from 1:1.5 to 1:10.
[0041] To stabilize the microencapsulated monomer droplets in the
aqueous phase, dispersing agents are used. Suitable dispersing
agents are naturally occurring or synthetic water-soluble polymers,
such as gelatin, starch, polyvinyl alcohol, polyvinylpyrrolidone,
polyacrylic acid, polymethacrylic acid, or copolymers made of
(meth)acrylic acid or of (meth)acrylates. Also highly suitable are
cellulose derivatives, particularly cellulose esters and cellulose
ethers, such as carboxymethylcellulose and hydroxyethylcellulose.
The amount of the dispersing agents used is generally from 0.05 to
1% (preferably from 0.1 to 0.5%), based on the aqueous phase.
[0042] In one particular embodiment of the present invention, the
polymerization is carried out in the presence of a buffer system.
Preferred buffer systems establish a pH of from 12 to 3 (preferably
from 10 to 4) for the aqueous phase at the start of the
polymerization. Particularly highly suitable buffer systems
comprise phosphate salts, acetate salts, citrate salts, or borate
salts.
[0043] During the polymerization of the monomer mixture 1 it is
possible to use an inhibitor dissolved in the aqueous phase. Either
inorganic or organic substances may be used as inhibitors. Examples
of inorganic inhibitors are nitrogen compounds, such as
hydroxylamine, hydrazine, sodium nitrite, and potassium nitrite.
Examples of organic inhibitors are phenolic compounds, such as
hydroquinone, hydroquinone monomethyl ether, resorcinol,
pyrocatechol, tert-butyl pyrocatechol, and condensation products of
phenols with aldehydes. Other organic inhibitors are
nitrogen-containing compounds, such as diethylhydroxylamine and
isopropyl-hydroxylamine. Resorcinol is preferred as inhibitor. The
concentration of the inhibitor is from 5 to 1000 ppm (preferably
from 10 to 500 ppm, particularly preferably from 20 to 250 ppm),
based on the aqueous phase.
[0044] The monomer mixture 2 is preferably composed of from 82 to
99% by weight of styrene, from 1 to 10% by weight of
divinylbenzene, and from 0 to 8% by weight of acrylonitrile,
particularly preferably of from 86 to 95% by weight of styrene,
from 3 to 8% by weight of divinylbenzene, and from 2 to 6% by
weight of acrylonitrile. The monomer mixture 2 may also contain
free-radical generators. The free-radical generators described
above may be used here. It has been found that the use of
significant amounts of free-radical generator in the monomer
mixture 2 for the novel process is not disadvantageous. When
free-radical generators are used in the monomer mixture 2, bead
polymers with high monodispersity are still obtained. As long as
the monomer mixture 1 comprises an amount of free-radical generator
sufficiently great that it can also polymerize the monomer mixture
2, it is possible to dispense with separate addition of
free-radical generator in monomer mixture 2. The ratio of monomer
mixture 1 to monomer mixture 2 (seed/feed ratio) is generally from
1:0.5 to 1:10, preferably from 1:0.75 to 1:6.
[0045] The addition of the monomer mixture 2 in step (d) to the
partially polymerized microencapsulated monomer droplets takes
place at a temperature that has been selected so that at least one
of the free-radical generators from monomer mixture 1 or 2 is
active. Temperatures of from 60 to 90.degree. C. are generally
used. To achieve high polymerization conversions, it can be
advantageous to raise the temperature during the
polymerization.
[0046] The monomer is added over a prolonged period, such as from
10 to 1000 min, preferably from 30 to 600 min. The addition may
take place at a constant rate or at a rate which changes over time.
It is possible for the composition of monomer mixture 2 to alter
during the feed period, for example, by starting with a low
divinylbenzene content and continuously raising the divinylbenzene
content during the feed period, or vice versa.
[0047] The monomer mixture 2 may be added in pure form. In one
particular embodiment of the present invention, the monomer mixture
2 or a portion of this mixture is added in the form of an emulsion
in water. This emulsion in water may be produced in a simple manner
by mixing the monomer mixture with water while using an emulsifying
agent, with the aid of a high-speed stirrer or rotor-stator mixer.
The ratio of monomer mixture to water here is preferably from
1:0.75 to 1:3. The emulsifying agents may be ionic or nonionic in
character. Ethoxylated nonylphenols having from 2 to 30 ethylene
oxide units are examples of highly suitable materials, as is the
sodium salt of isooctyl sulfosuccinate.
[0048] To complete the polymerization of the monomer mixtures in
step (e), once the addition of the monomer mixture 2 has ended, the
reaction mixture is held at a temperature of from 60 to 140.degree.
C. (preferably from 90 to 130.degree. C.) for a period of, for
example, from 1 to 8 h.
[0049] After the polymerization, the bead polymer may be isolated
by conventional methods, for example, by filtering or decanting,
and may be dried if desired after one or more washes and, if
desired, may be screened.
[0050] The bead polymers obtained by the novel process are
particularly preferably suitable for preparing cation- or
anion-exchangers. Surprisingly, they have a particularly low
content of soluble polymer. This content is less than 0.8%,
preferably below 0.4%.
[0051] The novel bead polymers are monodisperse, that is to say
they have an extremely narrow particle size distribution. The
particle size distribution is the result of the particle size
distribution of the monodisperse monomer droplets produced in step
(a). The (90)/(10) value is below 1.5, preferably below 1.25.
[0052] The conversion of the bead polymers to cation exchangers
takes place by sulfonation. Suitable sulfonating agents are
sulfuric acid, sulfur trioxide, and chlorosulfonic acid. Preference
is given to sulfuric acid at a concentration of from 90 to 100%,
particularly preferably from 96 to 99%. The temperature during the
sulfonation is generally from 50 to 200.degree. C., preferably from
90 to 110.degree. C. and particularly preferably from 95 to
105.degree. C. It has been found that the copolymers according to
the invention can be sulfonated without adding swelling agents
(e.g. chlorobenzene or dichloro-ethane) and in the process give
homogeneous sulfonation products.
[0053] For many applications it is advantageous to convert the
cation exchanger from the acid form to the sodium form. This
ion-exchange takes place using sodium hydroxide solution at a
concentration of from 10 to 60%, preferably from 40 to 50%.
[0054] After ion-exchange, the cation exchangers may be further
purified using deionized water or using aqueous salt solutions, for
example, using sodium chloride solutions or sodium sulfate
solutions.
[0055] The cation exchangers obtained by the novel process have
particularly high stability and purity. Even after prolonged use
and repeated regeneration, they show no defects on the ion-exchange
beads and no leaching of the exchanger. They are also stable over
long periods under oxidative conditions.
[0056] The following examples further illustrate details for the
process of this invention. The invention, which is set forth in the
foregoing disclosure, is not to be limited either in spirit or
scope by these examples. Those skilled in the art will readily
understand that known variations of the conditions of the following
procedures can be used. Unless otherwise noted, all temperatures
are degrees Celsius and all percentages are percentages by
weight.
EXAMPLES
[0057] Determination of soluble content
[0058] To determine the soluble content, from 5 to 7 g of polymer
were weighed into an extraction holder and extracted overnight in a
Soxhlet apparatus using 800 ml of toluene (bath temperature
140.degree. C.). The extract was filtered through a suction funnel
using a blackribbon filter and concentrated to about 1 ml on a
rotary evaporator. 300 ml of methanol were then added, followed by
drying in vacuo on the rotary evaporator to constant weight. Two
determinations were carried out on each specimen.
EXAMPLE 1 (Comparative Example)
[0059] Example 1 of EP-A 826,704 (counterpart of U.S. Pat. No.
5,834,524) was repeated. The content of soluble polymer was
determined as 2.3%.
EXAMPLE 2 (Inventive)
[0060] Preparation of a bead polymer
[0061] A mixture of 98.75 parts of styrene, 1.25 parts of 80%
strength divinylbenzene (in ethylbenzene), and 0.5 part of
tert-butyl peroxy-2-ethylhexanoate (monomer mixture 1) was
dispersed with the aid of a die plate with vibrational excitation
to give droplets with an average particle size of 245 .mu.m and a
(90)/(10) value of 1.06 in an aqueous phase. As described in
Example 1 of EP 46,535 B1 (counterpart of U.S. Pat. No. 4,427,794),
the monomer droplets in a column were encapsulated with a complex
coacervate made of gelatin and a copolymer made of acrylamide and
of acrylic acid as coacervate component. The monomer droplets were
then hardened by adding formaldehyde and freed from excess gelatin
and excess copolymer, as well as formaldehyde, by countercurrent
washing. 999.7 g of an aqueous mixture containing 503.0 g of
microencapsulated monomer droplets, prepared by the above process,
were mixed with an aqueous solution containing 12.0 g of gelatin,
20.0 g of sodium hydrogen phosphate dodecahydrate, and 200 mg of
resorcinol in 1560 ml of deionized water in a 4-liter glass
reactor. The mixture was polymerized at 75.degree. C. for 10.5 h,
with stirring (stirrer speed 200 rpm). After a polymerization time
of 3.5 h the conversion reached 20%, and monomer mixture 2
containing 1297 g of styrene, 197 g of 80% strength
divinyl-benzene, and 3 g of dibenzoyl peroxide was added dropwise
over a period of 5 h at a constant rate. After completion of the
polymerization phase at 75.degree. C., the mixture was held for 2 h
at 95.degree. C. The mixture was washed on a 32 .mu.m screen and
dried to give 1892 g of a bead polymer with a smooth surface.
Visually, the polymers appeared transparent; the average particle
size was 370 .mu.m and the (90)/(10) value was 1.06. The bead
polymer had a soluble content of 0.20%.
EXAMPLE 3 (Inventive)
[0062] Preparation of a bead polymer
[0063] A mixture containing 98.75 parts of styrene, 1.25 parts of
80% strength divinylbenzene, and 0.5 part of tert-butyl
peroxy-2-ethylhexanoate (monomer mixture 1) was dispersed with the
aid of a die plate with vibrational excitation to give droplets
with an average particle size of 292 .mu.m and a (90)/(10) value of
1.24 in an aqueous phase and microencapsulated as described in
Example 2.
[0064] 999.7 g of the aqueous mixture comprising 503.0 g of
microencapsulated monomer droplets were mixed with an aqueous
solution made of 6.0 g of gelatin, 20.0 g of sodium hydrogen
phosphate dodecahydrate, and 200 mg of resorcinol in 1560 ml of
deionized water in a 4-liter glass reactor. The mixture was
polymerized at 75.degree. C. for 15.5 h, with stirring (stirrer
speed 200 rpm). After a polymerization time of 3.5 h the conversion
reached 20%, and monomer mixture 2 containing 1217 g of styrene,
138 g of 80% strength divinylbenzene, 80 g of acrylonitrile, and 3
g of dibenzoyl peroxide was added dropwise over a period of 10 h at
a constant rate. After completion of the polymerization phase at
75.degree. C., the mixture was held for 1 h at 95.degree. C. The
mixture was washed on a 32 .mu.m screen and dried to give 1805 g of
a bead polymer with a smooth surface. Visually, the polymers
appeared transparent; the average particle size was 410 .mu.m and
the (90)/(10) value was 1.24. The bead polymer had a soluble
content of 0.29%.
EXAMPLE 4 (inventive)
[0065] Preparation of a bead polymer
[0066] Example 2 was repeated except that monomer mixture 1 was 520
g of a mixture containing 96.25 parts of styrene, 3.75 parts of 80%
strength divinylbenzene, and 0.5 part of tert-butyl
peroxy-2-ethylhexanoate. The average particle size of the
microencapsulated monomer droplets was 295 .mu.m and the (90)/(10)
value was 1.08.
[0067] 1033.5 g of an aqueous mixture comprising 520 g of
microencapsulated monomer droplets were mixed with an aqueous
solution made of 12.0 g of gelatin, 20.0 g of sodium hydrogen
phosphate dodecahydrate, and 200 mg of resorcinol in 1500 ml of
deionized water in a 4-liter glass reactor. The mixture was
polymerized at 75.degree. C. for 9.5 h, with stirring (stirrer
speed 200 rpm). After a polymerization time of 3.5 h the conversion
reached 25%, and monomer mixture 2 containing 803 g of styrene,
64.6 g of divinylbenzene, and 1.74 g of 80% strength dibenzoyl
peroxide was added dropwise over a period of 4 h at a constant
rate. After completion of the polymerization phase at 75.degree.
C., the mixture was held for 2 h at 95.degree. C. The mixture was
washed on a 32 .mu.m screen and dried to give 1274 g of a bead
polymer with a smooth surface. Visually, the polymers appeared
transparent; the average particle size was 405 .mu.m and the
(90)/(10) value was 1.08. The bead polymer had a soluble content of
0.25%.
EXAMPLE 5 (Inventive)
[0068] Preparation of a bead polymer
[0069] Example 4 was repeated except that monomer mixture 2 was a
mixture of 775.6 g of styrene, 64.6 g of divinylbenzene, 27.8 g of
acrylonitrile and 1.74 g of 80% strength dibenzoyl peroxide.
Monomer mixture 2 was added dropwise after 4.5 h of polymerization
time, corresponding to a polymerization conversion of 35%, over a
period of 4 h at a constant rate. The mixture was held for a total
of 10.5 h at 75.degree. C. and then 4 h at 95.degree. C. The
mixture was washed on a 32 .mu.m screen and dried to give 1321 g of
a bead polymer with a smooth surface. Visually, the polymers
appeared transparent; the average particle size was 415 .mu.m and
the (90)/(10) value was 1.08. The bead polymer had a soluble
content of 0.30%.
EXAMPLE 6 (Inventive)
[0070] Preparation of a bead polymer
[0071] Example 2 was repeated except that monomer mixture 1 was 892
g of a mixture containing 93.75 parts of styrene, 6.25 parts of 80%
strength divinylbenzene, and 0.5 part of tert-butyl
peroxy-2-ethylhexanoate. The average particle size for the
microencapsulated monomer droplets was 320 .mu.m and the (90)/(10)
value was 1.06.
[0072] 1773 g of an aqueous mixture comprising 892 g of
microencapsulated monomer droplets were mixed with an aqueous
solution made of 12.0 g of gelatin, 20.0 g of sodium hydrogen
phosphate dodecahydrate, and 200 mg of resorcinol in 1248 ml of
deionized water in a 4-liter glass reactor. The mixture was
polymerized at 75.degree. C. for 8.5 h, with stirring (stirrer
speed 200 rpm). After a polymerization time of 2.5 h the conversion
reached 15%, and monomer mixture 2 made of 780.4 g of styrene, 19.9
g of 80% strength divinylbenzene, and 2.1 g of dibenzoyl peroxide
was added dropwise over a period of 4 h at a constant rate. After
completion of the polymerization phase at 75.degree. C., the
mixture was held for 4 h at 95.degree. C. The mixture was washed on
a 32 .mu.m screen and dried to give 1421 g of a bead polymer with a
smooth surface. Visually, the polymers appeared transparent; the
average particle size was 385 .mu.m and the (90)/(10) value was
1.06. The bead polymer had a soluble content of 0.20%.
* * * * *