Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
OOZ. 0050/034090
Preparation~ polymer powders
The present invention relates to a process for
the preparation of a polymer powder from a polymerizable
monoethylenically unsa-turated compound by polymerizing
the monomer in a powder bed in the presence of a con-
ventional polymeri~ation initiator, whilst maintaining
the reaction mixture in the form of a powder and causing
it to circulate.
French Patent 1,117,753 discloses the preparation
of hydrophobic polymers, such as poIyvinyl chloride, by
polymerizing ethylenically unsaturated monomers, in the
presence of a diluent and of a polymerization initiator,
in a polymer powder, whilst mixing the reaction mixture
and maintaining it in the form of a powder during the
polymerization. The polymerization can also be
carried out in the absence of a diluent~ by using an ex-
cess o~ the monomer and removing the heat of polymeriza-
tion by evaporating the liquid monomer from the polymer-
ization zone~ Where a diluent is used, water is
employed and serves to remove, from the system, the heat
generated during polymerization. The water is con-
densed and recycled to the reaction mixture. It is
not possible to produce hydrophilic polymers in powder
form by this process, because the water which accumulates
in the polymerization zone dissolves or swells the hydro-
philic polymers so that the polymer particles agglomerate.
U.S. Patent 4,135,043 discloses a process for the
preparation of hydrophilic polymers in powder form, in
which water is the sole auxiliary liquid used. How-
'~
ever, the use of water as a diluent has some disadvantages,
because the polymerization of the monomers in part commences in
the devices used to feed the monomers into the polymerizatlon
zone, and the polymerization must be carried out at far above
100C in order to remove the water, under atmospheric pressure,
from the polymerization zone.
It is an object of the invention to provide a process
for the preparation of polymer powders, by means of which both
water-soluble and water~insoluble monomers can be polymerized
and which gives polymer powders which have a low residual monomer
content.
We have found that this object is achieved, in the
process described at the outset, if the monomex which boils at
above +5C under l,013 mbar which monomer is dissolved or emul-
sified, at from 5 to S0~ strength, in an inert organic solvent
which is a precipitant for the polymer, is brought into contact
with the powder bed and the organic solvent is removed, as vapor,
from the polymerization zone.
The polymerization is preferably carried out in the
absence of water. However, the solvent may contain up to 10%
by weight of water. rrO prepare polymers having a particularly
low residual monomer content, a final polymerization is carried
out by either adding to the reaction mixture, after the main
polymerization, a polymerization initiator which decomposes at
a higher temperature than does the initiator used for the main
polymerization, or employing a mixture of these two initiators
even for the main polymerization and then carrying
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out the final polymerization at from about 10 to 100C
above the temperature used ~or -the main polymerization.
In this way, polymer powders of various particle size dis-
tributions are obtained direct;. The particle size
distribution depends in a complex manner on the reaction
conditions, on the composition o~ the initiator system
and on the intensity with which the reaction mixture is
caused to circulate in the polymerization zone~ -
~ he process according to the invention is prefer-
lo entially used for homopolymerizing or copolymerizing
polymerizable water-soluble ethylenically unsaturated
compounds. These monomers form hydrophilic polymers.
Examples of suitable water-soluble monomers are ethyleni-
cally unsaturated C3-C5-monocarboxylic acids, dicarboxy-
lic acids and their anhydrides, for example acrylic acid,
methacrylic acid, maleic acid, maleic anhydride, fumaric
acid and itaconic acid, amides o~ ethylenically unsatura-
ted carboxylic acids, preferably acrylamide and meth-
acrylamide, and basic acrylamides and methacrylamides,
such as dialkylaminoalkylacrylamides or dialkylamino-
alkylmethacrylamides, egO dimethylaminoethylacrylamide,
dimethylaminopropylacrylamide and diethylaminoethylacryl-
amide, esters of ethylenically unsaturated carboxylic
acids with aminoalcohols, eg. aminoethyl acrylate, di-
methylaminoethyl acryla-te, diethylaminopropyl acrylate
and dimethylaminoethyl methacrylate, vinylpyrrolidone
and its derivatives, vinylimidazole and substituted vinyl-
imidazoles, and vinylsulfones. The ethylenically
~OZ. ~050/034090
unsaturated carboxyllc acids can ~lsobe employed in a neutralized or partially neutralized
~orm, where such forms are soluble in the organic solvent.
me monomers mentioned may be homopolymerized or copoly-
merized; for example, copol~mers of acrylamide and
acrylic acid, copolymers of methacrylamide 9 dimethylamino-
ethyl acrylate and acrylic acid, and copolymers of acryl-
ic acid and acrylonitrile, or homopolymers of the mono-
mers, can be prepared.
The polymerization can be carried out in the
presence of crosslinking agents in order to increase the
molecular weight of the polymers.- These crosslinking
agents are compounds which are copolymerizable with the
monomers and possess two or more ethyleni-
cally unsaturated bondsO Examples of suitable
crosslinking agents are butanediol diacrylate, methylene-
bis-acrylamide, divinyldioxane, ethylene-divinylurea and
pentaerythritol triallyl ether. The crosslinking co-
monomers possessing two or more double bonds are employed
in the polymerization in an amount of at most 5% by
weight, preferably from 0.5 to 2% by weight9 based on
total monomers. If only partial crosslinking of the
polymers is necessary, these amounts are reduced to from
0 001 toO.1% by weight.
Examples of suitable water-insoluble polymeriz-
able ethylenically~ unsaturated compounds are styrene,
acrylonitrile, methacrylonitrile 9 esters of acrylic acid
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and methacrylic acid with Cl C'8-alcohols~ vinyl esters
of C2-Cl2-carboxylic acids, monoesters and diesters of
maleic acid 9 and vinyl ethers eg. vinyl methyl ether,
vinyl butyl ether and vinyl cyclohexyl ether. To
polymerize the monomers, they are ~irst dissolved or
emulsified in an iner-t organic solvent.
Examples of suitable solvents are ketones, eg.
acetone and methyl ethyl ketone, hydrocarbons 9 such as
saturated aliphatic hydrocarbons, eg. pentane, hexane,
heptane, octane, isooctane and cyclic aliphatic hydro-
carbons, such as cyclohexane and decalin, aromatic hydro-
carbons, çg. benzene, toluene and xylene, aliphatic halo-
hydrocarbons, eg. l,l 9 2-trichloro-l12,2 trifluoroethane
and trichlorofluoromethane, ethers 7 eg. dimethyl ether,
diethyl ether, methyl tert.-butyl ether, tetrahydrofuran
and dioxane, esters, eg, methyl acetate and ethyl acetate 9
alcohols, eg. monohydric Cl-C8-alcohols, lactones, eg.
~-butyrolactone 9 dimethylsulfoxide, dimethylformamide
and nitromethane.
The preferred solvents are acetone, n-hexane,
cyclohexane and methyl tert.-butyl ether. In prin-
ciple~ all organic solvents which are inert under the
polymerization conditions and which virtually do not re-
act with the reactants present in the polymerization,
may be us~d, However, the inert solvents affect the
particle size distribution and the molecular weigh-t of
the polymers, since they can to a greater or lesser de-
gree act as regulators. The boiling point of the inert
organic solven~scan De from -25 to ~;~0C under atmospheric
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conditions. Inert organic solvents which boil at from
20 to 150C are preferred. The solvent must be sel-
ected so as not to dissolve the polymer. I~ the mono-
mer is incompletely soluble in the inert sol~ent, it is
emulsified therein. For -this purpose, an emulsifier
must in some cases be used. Examples of suitable
emulsifiers are fatty acid esters of sorbitolf
ethylene oxide/propylene oxide copolymers, oxyethylated
fatty acids, phenols, clO Cl8-alcohols and C10-cl8-~mines,
The emulsifiers are used in amounts of from 0.01
to 1% by weight, based on monomers.
According -to the invention, the polymerization is
carried ou~ in a powder bed. Suitable powders inc-
lude both inorganic and organic materials in powder form,
~or example quartz powders, talc, alumin~, carbon black,
- wood flour, sodium chloride and glass beads. Suitable
inorganic materials in powder form include not only inert
materials but also 9 for example, sodium carbonate, pot-
assium carbonate, ammonium carbonate, ammonium carbamate,
sodium bicarbonate 9 alkaline earth metal oxides, eg
magnesium oxide and calcium oxide, magnesium carbonate
and calcium carbonate. If the last-mentioned powders
are used, pol~merization of monomers containing acid
groups yields partially or completely neutralized poly-
mers. Preferably, however, the powder initially intro-
duced into the polymerization zone is an inert polymer
powder which corresponds to the composition of the poly~
- 7 - o~z. 0050/~3~090
mer being freshly formed from the monomer mixture or
from the monomer to be polymerized. If no polymer
powder is available, these poLymers may be prepared by
conventional polymerization processes, for example by
mass-polymerizing the monome~ and comminuting the solid
polymer, or by polymerizing the monomers in a water-in-
oil emulsion and precipitating and isolating the polymer
formed, or by precipitation polymerization or bead
polymerization.
Examples of suitable polymerization reactors are
kettles or stirred autoclaves, which may or may not be
arranged as a multi-stage cascade, or combinations o~
stirred kettles with a downstream flow tube.
The material in thepolymerization zone ~ maintained
in the form of a powder over the entire duration of the
polymerization. Preferably, the monomer solution or
emulsion is applied in a finely divided form to the pow~
der in the polymerization zone. As a rule, this step
is carried out by spraying the solution or emulsion.
The monomer solution can be sprayed onto the powder bed
or be atomized directly in the powder bed. The mono-
mers are introduced, continuously or in portions, into
the polymerization zone, a-t the rate at which they poly-
merize During the polymerization, the reaction mix-
ture mus-t be caused to circulate adequately. Prefer-
ably, this is done by stirring the mixture. The heat
generated during pol~nerization, and the heat generated
by circulating the powder, are removed by continuously
evaporating the solvent from the reaction zone. Pre-
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ferably, the concentration of the monomers in the organ
ic solvent is selected to be such that on complete
polymerization of the monomers the enthalpy of polymeri-
zation which is liberated just; suffices to remove the
organic solvents completely by evaporation, under the
prevailing reaction conditions, from the polymerization
zone. The concentration of the monomers in the sol-
vent is preferably in the range from 15 to 35% by weight.
The polymerization is carried out with the aid
lo of the conventional free radical catalysts. Examples
of suitable catalysts are peroxides, hydroperoxides, azo
compounds and C~C-labile compounds. The polymeriza-
tion initiators can also bé employed conjointly with a
suitable accelerator. Suitable accelerators are
reducing compounds, preferably amines derived from
(saturated) cyclic compounds or from phenyl compounds,
and are used by themselves or in the presence of an or~
ganic compound of a transition metal. The pol~meri-
zation initiators can be introduced into -the polymeriza-
tion zone either together with the monomer solution oremulsion or separately therefrom. If the heat
liberated by the polymerization, together with the heat
generated by stirring or by neutralization, if any, does
not su~fice to remove the solvent from the system, it is
necessary additionally to supply heat to the reaction
mixture so that the solvent is completely removed from
the polymerization zone during the polymerization and the
reaction mixture is maintained in the form of a powder.
If on the other hand the amount o~ solvent should be too
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~ 9 - o.Z~ OOS0/03~090
low to remove the entire heat generated during the poly-
merization, it is necessary to cool the reaction mixture~
The polymerization of the monomers can be carried
out a-t ~rom -25 to 160C, preferably from 20 to 100C,
depending on the reactivity of the monomers and the
ef~ectiveness of the initiator system. Since the re-
action mixture is maintained in the ~orm of a powder
throughout the polymerization 7 the polymerization
temperature is about 10C below the melting point or
incipient softening range of the polymer 9 SO that no
agglomeration occurs. The polymerization can be
carried out under atmospheric pressure, under reduced
pressure or under superatmospheric pressure of up to 25
bar, pre~erably up to 4 bar. The novel process can
be carried out batchwise or continuously, and in both
cases suitable containers for the reaction zone are, ~or
example, stirred kettles or dynamic mixers o~ all kinds.
In continuous operation, the monomer solution or emul-
sion is mixed with the initiator system and then fed to
the reaction zone continuously or at intervals, and the
polymer is continuously or intermittently removed ~rom
the reaction zone by a suitable discharge device, for
example a screw. Per unit time, about the same amount
of polymer is removed as the amount o~ monomer introduced
into the reaction zone. Advantageously, the monomer
solution and the initiator system are cooled be~ore being
introduced into the reaction zone, ie. the temperature o~
the monomer solution is ~rom -40 to +20C.
In order to obtain a polymer powder having a
~ 10 - O.Z~ 0050/034090
particularly lo~ monomer content, the main polymerization
is followed by a final polymerization. For this
purpose, the reaction mixture is heated to 10 100C above
the temperature at which the main polymerization has been
carried out. To polymerize the residual monomer a
polymerization initiator which decomposes at a higher
temperature is preferably added to the monomer from the
start, but it is also possible to spray a solution of
the initiator in an organic solvent onto the reaction
mixture after conclusion of the main polymerizationO
In this last-mentioned case, the same initiator as is
used in the main polymerization may be employed. Pre-
ferably~ however, the initiator used for the final poly-
merization decomposes at a higher temperature than the
initiator used for the main polymerization. For the
final polymerization, from 0.05 to 0.8, preferably from
0.15 toO.5~mole % ~ polymerization initiator is used per
mole ofmonomerormonomermixture. The decomposition tempera-
tures which correspond to a half-life of 1 hour differ
by at least 20C between the polymerization initiator
for the main polymerization and for
the final polymerization. Where mixtures
of polymerization initiators are employed, from 0.1 to
5 mole %, based on monomers, of the polymerization
initiator having the lower decomposition temperature,
\
- 11 O~Z0 0050/034090
and from 0~05 to 0.8 mole %, based on monomers, of the
polymerization initiator having the higher decomposition
temperature, are used. The polymer powders ob-tained
have particle diameters of from 10 ~m to 2 cm, preferably
~rom 0.1 to 5 mm.
The polymers prepared by the process according
-to the invention have a different molecular weight dis-
tribution from those obtained, for example, by precipi
tation polymerization or by polymerization in a water-in-
oil emulsion. Compared with precipitation polymeri-
zation, the novel process gives a substantially higher
space-time yield. Furthermore, the conventional
working-up steps for isolating and drying the polymers
are not needed.
me polymers obtained by the novel process are
employed for the conventional purposes of these materials.
For example, copolymers of acrylamide and acrylic acid
are employed as flocculating agents in the paper indus-
try~ in mining and in sewage farms, water-soluble alkali
metal salts or alkaline earth metal salts of copolymers
of acrylonitrile and acrylic acid are used as textile
sizes-~ partially neutralized copolymers of styrene and
maleic anhydride are used as paper sizes, homopolymers
and copolymers of acrylonitrile are used as agents for
increasing the strength of paper, and copolymers of N-
~inylpyrrolidone are used as hair strengtheners in cos-
metics.
In the Examples which follow, parts and percent-
ages are by weight. The K values were determined by
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the method of H. Fikentscher, Cellulosechemie 1~ (1932),
58-64 and 71-74, at 25C; K = k 0 103
EXAMPLE 1
Preparation of a copolymer of styrene and maleic anhy~
dride
This copolymer was produced batchwise. The
polymerization vessel was a cylindrical glass vessel o~
5 liters capaclty 9 equipped with a spiral stirrer and a
descending condenser. A spray nozzle opened into the
glass vessel and the monomer solution, togeth~r with the
initiator, was sprayed from this nozzle onto the polymer
powder initially introduced into the vessel. A
nitrogen line furthermore led into the glass vessel so
that the polymerization could be carried out under a
nitrogen atmosphere. The vessel was heated by means
of an oilbath. The monomer solution was mixed with
the initiator solution in a static mixer. A heat
exchanger was built into the line through which the mono-
mer was fed to the static mixer, so that the monomer
solution could be cooled if required.
A tap was built into the line leading to the condenser
so as to be able to separate out solids entrained by the
stream of nitrogen or by the evaporating inert organic
solvent 1,500 g o~ a nylon powder obtained from
adipic acid and hexamethylenediamine and having a
particle diameter of 1-2 mm were initially introduced
into the apparatus described above and heated to 80C,
with vigorous circulation.
A solution of 625 g of styrene and 625 g of
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maleic anhydride in 39750 g ~ methyltert,-butyl e~r was
combined9inthestatic mixer9ina volumetric flow ratio oflO:l,
with an initiator solution of 14.8 g of bis-(4-tert.-butyl-
cyclohexyl) peroxydicarbonate in 500 ml of methyl tert.-
butyl ether, and the mixture wasprogressively sprayed,
over 4.5 hours 9 onto the agitated solid-particle bed of
nylon powder. The polymerization temperature was
75C, During the polymerization, the reaction mix-
ture was maintained in the form of a powder in the poly-
lo merization zone and the solvent, namely methyl tert,-
kutyl ether, was continuously evaporated from the re-
action zone by the heat liberated by polymerization and
by the energy introduced into the system as a result of
stirring the powder bed, and was condensed in the des-
cending condenser, The copolymer of styrene and
maleic anhydride, separated from the inert material
initially introduced, was solvent-free and had a K value
of 33.5 (0.2% strength solution in toluene), Resi-
~ual monomers were not detectable.
The copolymer was soluble in dilute aqueous
sodium hydroxide solution and was used, in a partially
or completely neutralized form, as a paper size,
EX~PLE 2
Preparation of polystyrene
Using the polymerization apparatus described in
Example 1, 1,500 g of polystyrene of particle diameter
1-2 mm were introduced and heated to 94C, with constan-t
circulation, A solution of 300 g of styrene in
2,100 g of n-hexane was then combined in a static mixer,
- 14 ~ o~z~ 0~50~034090
in a volumetric flow ratio of lO :19 with a sol~tion of
13.8 g of a polymerization initiator, namely bis-(4-ter~.-
butylcyclohexyl) peroxydicarbonate, in 500 ml of n-hexane
an~ the mixtllre was sprayed continuously, over 6
hours, onto the solid-particle bed of polystyrene.
The polymerization temperature was soc. . During the
polymerization, the material in the polymerization zone
was maintained in the fo~m of a powder and the solvent
was distilled off continuously. A solvent-free
lo polymer having a K value of 60~4 (measured in 0.2%
strength solution in toluene) and a residual monomer
content of 0.45~ was obtained.
~he polymer powder ~as used for the production
of moldings or, after impregnation with a blowing agent
(eg. pentane), for the production of foam moldings.
EXAMPLE 3
Preparation of polymethyl methacrylate
1,200 g of magnesium oxide o~ particle diameter
0.1 ~m were initially introduced into the apparatus des-
cribed in Example l. The temperature of the oilbath
2G was set to 100C. A solution of l,000 g of methyl meth~
~crylate in 3,000g of n-hexane wascombined,in thestaticmixer,in a
vQlumetric flow ratio of lO:l, with a solution of 10.5 g
of a polymerization initiator, namely bis-(4-tert.-
butylcyciohexyl) peroxydicarbonate, in 500 ml of n-hex-
ane, and the mixture was sprayed progressively, over 4
hours~ onto the agitated solid-particle bed. During
the polymerization, the reaction mixture was maintained
in the form of a powder and the solvent was distilled
- 15 - O.ZO 0050/034090
off continuously. The po]ymethyl methacrylate,
detached from the inert starting material~
had a K value of 48 (measured in 0.2% strength solution
in acetone) and a residual monomer content of 0~8%.
The polymer was used for the production of moldings.
EXAMPLE 4
Preparation of a copolymer of acrylamide and sodium
acrylate
1,500 g of polyacrylamide having a K value of 53
and 616 g of sodium bicarbonate were introduced into the
polymerization apparatus described in Example 1, and the
oilbath was brought to 90C~ A solution of 600 g of
acrylic acid and 400 g o~ acrylamide dissolved in 3,000
g of acetone, and an initiator solution consisting of
16.6 g of bis-~4~tert.-butylcyclohexyl) peroxydicarbonate
in 500 ml of acetone were then brought together, in a
volumetric flow ratio of 10:1, by means of a static mixer,
and the mixture was sprayed onto the agitated material
initially introduced into the apparatus. During the
polymerization9 the reaction mixture was maintained in
the form of a powder and the acetone was distilled from
the polymerization zone. The polymerization tempera-
ture was 75C. The sodium salt of a copolymer of
acrylamide and acrylic acid was obtained; it dissolved
~ery readily in water, with virtually no evolution of
carbon dioxide. The copolymer was virtually free
from acetone and had a K value o~ 52.8 (determined in
5% strength NaC1 solution~. The residual monomer
content was 2.40~o. `
~9~
~ 16 - o~zO 005/034090
To reduce -the residua:L monomer content, the
material was subjected to a final polymerization by
spraying a solution of 5 g of benzoyl peroxide in 100 g
of acetone onto the agitated copolymer, at 100C. The
residual monomer content fell to about 0.1%, with a
slight drop in K value to 51.5.
The copolymer was used as a flocculating agent
in sewage farmsO
EXAMPLE 5
Preparation o~ a copolymer o~ acrylamide and ammonium
acrylate
1,500 g of polyacrylamide9 of K value 5~, were
introduced into the apparatus described in Example 1.
The reacti~n chamber was exposed to gaseous ammonia and
the temperature of the oilbath was brought to 90C, A
solution of 600 g of acrylic acid and 400 g o~ acryl-
amide in 3,000 g of methyl tert.-butyl ether was then
combined, in a vvlumetric ~low ratio of 10 1 in a static
mixer, with an initiator solution consisting of 16~6 g
of bis-(4 tert.-butylcyclohexyl) peroxydicarbonate in
500 ml of methyl tert.-butyl ether, containin~ 10% of methanol7
and the mixture was sprayed continuously, over 4
hours, onto the agitated material initially introduced.
During the polymerization, the solid-particle bed was
circulated e~ficiently and ammonia was passed into the
polymerization zone. The polymerization -temperature
was 75Cc The methyl tert.-butyl ether introduced
into the polymerization zone together with the monomer
was removed continuously from the reaction zone, during
- 17 -
the polymerization, by evaporation. After completion
of the addition of the monomer solution and of the poly-
merization initiator the mixture was
kept at 90C for a further 30 minutes. A copolymer
of acrylamide and ammonium acrylate, which had a K value
of 46 and was virtually odorless, was obtained. The
particle diameter o~ the polymer was from 0.1 to 2 mm.
Aqueous solutions of the copol-ymer were used as floccu-
lating agen~ in papermaking.
EXAMPLE 6
lo Preparation of polyacrylamide
1,500 g of polyacrylamide having aK value of 53 and a
mean particle diameter of 1 mm were introduced into the
polymerization apparatus described in Example 1. The
oilbath was brought to 90C. A solution of 1,000 g
of acrylamide and 1.2 g of methylene-bis-acrylamide in
3,000 g of acetone was then combined with a solution of
16.6 g of a polymerization initiator, namely bis-(4-
tert.-butylcyclohexyl) peroxydicarbonate, in 500 ml of
acetone, in a volumetric flow ratio of lO:l,by means of
a static mixer and the mixture was sprayed progressively,
over 4 hours, onto the agitated polyacrylamide pow~er.
During the polymerization, the reaction mixture was main-
tained in the form of a powder and the acetone was con-
tinuously removed from the polymerization zone by evaporation.
The polymerization temperature was 75C. A virtually
non-hydrolyzed polyacrylamide was obtained, which was
com~le-tely soluble in water and had a K value of 67.
The par-ticle diameter of the polymer was from 0.1 to 2 mm.
~9~6~
~ 18 - o~ ooSo/o34o9o
Aqueous solutions of the copolymer were used as a paper
strengthener.
EXAMPLE 7
Preparation of polyacrylamide
The polymerization apparatus used was a steel
pressure kettle which was equipped with a spiral stirrer
and had a capacity of 40 liters. The solution of
the monomer and the solution of the polymerization
initia-tor were mixed in a temperature-controlled spray
lance and the mixture was sprayed onto the inert material,
in powder form, which had first been introduced into the
pressure kettle. The powder formed during thepolymeri-
zation wa~s discharged from the polymerization zone by
means of a screw.
15 kg o~ polyacrylamide, having a K value of 53
and a particle diameter of from 1 to 4 mm were ~irst
introduced into the pressure kettle. The temperature
of the heating was
set to 80C. 8 liters per hour of a 25% strength
solution o~ acrylamide in acetone and 600 ml/hour of a
solution in acetone of 0.18 mole % of bis-(4-tert.-butyl-
cyclohexyl) peroxydicarbonate and 0.072 mole% of tert~-
butyl peroctoate, the percentages being based on acryl-
amide~ were then combined by means of a static
mixerg and the mixture of the monomer and the
polymerization initiators was sprayed onto the poly-
acrylamide powder bed over 70 hours. During the
- 19 - o~z~ 0050~03~090
polymerization, the reaction mixture was maintained in
the form of a powder and the acetone was removed com-
pletely from the reaction chamber, as vapor, due to the
heat of polymeriza-tion and the energy introduced by stir-
ring. The polymer powder formed during the polymeri-
zation was discharged by means of a screw. The poly-
merization temperature was 75C. 150 kg of freshly
formed polymer, having a particle diameter of from 0.1 to
5 mm and a K value of 62 (determined in 0 2% strength
aqueous solution) were obtained.
EXAMPLE 8
15 kg of polyacrylamide having a K value of 53
and a particle diameter of from 1 to 4 mm were introduced
into the continuous polymerization apparatus described in
Example 7. The heating of the pressure kettle was set to
&oc. 8 liters per hour of a 25~ strength solution of
acrylamide in acetone, containing 5~ of water, and 500 ml
per hour of an initiator solution in acetone
containing 0 15 mole % of bis-(4-tert. butylcyclohexyl)
p~rôxydicarbonate, 0.06 mole % of tert.-butyl peroctoate
and 0 024 mole % of dibenzoyl peroxide, the percentages
being based on acrylamide, were
combined by means of a static mixer, and the mixture was
sprayed, over a period of 70 hours,onto the solid-particle
powder bed. During the polymerization, the bed
was circulated continuously and the solvent, as well as
the water introduced with the solvent into the polymeri-
- 20 ~ O~Z~ 0050/034090
zation zone, were evaporated continuously, thereby main-
taining the reaction mixture in the form of a powder
during the polymerization. The polymerization
temp~rature was 75C. 150 kg of freshly formed poly-
acrylamide were obtained; this material was solvent-
free and had a K value of 87 (determined in 0 2% strength
aqueous solution) and a residual monomer content of 0.9%.
20 kg of this polyacrylamide were subjected to
a final polymerization by heating for 4 hours at 110C~
which caused the decomposition of the polymerization
initiators (tert.-butyl peroctoate and dibenzoyl perox-
ide) present in the product. The residual monomer
content fell to about 0.1%, the K value of the product
being 86.
EXAMPLE 9
Preparation of a copolymer of 80% of acrylamide and 20~o
o~ acrylic acid
15 kg of polyacrylamide having a K value of 5~
of 53 and a particle diameter of from 1 to 4 mm were
introduced into the polymerization apparatus described
in Example 7. The protective heating of the kettle
wa~ set to 80Co 8 liters per hour of a 25% strength
. solution o~ 80% of acrylamide and 20~ of acrylic acid in
acetone and 700 ml per hour of an initiator solution in ace-
tone of 0.21 mole %of bis-(4 tert.-butylcyclohexyl peroxydi-
carbonate and 0.084 mole % o~ tert.-butyl peroc-toate 9
the percentages being based on monomer
mixturet were then combined by means o~ a s-tatic mixer,
and the mixture was sprayed 9 over 6~ hours, onto the
6~
- 2~ - O.Z. 0050/034090
solid-particle bed, the reaction mixture being maintained
in the form of a powder The polymerization tempera-
ture was 75C. The acetone was evaporated conti~uous-
ly from the polymerization zone 1~5 kg of freshly
formed virtually solvent-free copolymer were obtained,
the product having a K value of 80 (de-termined in 5%
strength NaCl solution) and a particle diameter of from
1 to 5 mm.
EXAMPLE 10
Preparation of polyvinylpyrro7idone
1,500 g of a dry polyvinylpyrrolidone powder
having a particle diameter of from 1 to 2 mm were intro-
duced into the polymerization apparatus described in
Example 1. The oilbath was brought to 90C. A
30% s~rength solution of N-vinylpyrrolidone in cyclohex-
ane was then combined with an initiator solution, ~mely a
5% strength solution of azodiisobutyronitrile in cyclo-
hexane 3 in a volumetric flow ratio o~ 10:1 in a static
mixer, and the mixture of monomer and-polymerization
initiator was sprayed continuously, over a period of 5
hours, onto the constantly agi-tated solid particle bed.
The polymerization temperature was 85C. During the
polymerization 7 the cyclohexane was removed continuously
~rom the polymerization zone under slightly reduced
pressure. A polyvinylpyrrolîdone powder which had a
K value o~ 60 (determined in 5% strength NaCl solution)
and a particle diameter of from 0.1 to 4 mm was obtained.
This product gave a clear solution in water.
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~ LE 11
Prepara~ion of a copolymer of'N-vinylpyrrolidone and
vinyl acetate
19500 g of a polyvinylpyrrolidone powder having
a particle diameter of from 1 to 2 mm were i~troduced
into the polymerization apparatus described in Example 1.
The oilbath was brought to 90C. A 30% strength
solution of 80% of N-vinylpyrrolidone and 20% of vinyl
acetate in hexane, and an initiator solution, namely a
5~0 strength solution of azodiisobutyronitrile in hexane,
were combinedg in a volumetric flow ratio of 10:1, by
means of a static mixer, and sprayed progressively, over
a period of 5 hours, onto the agitated solid-particle
bed, During the polymerization, the reaction mixture
was maintained in the form of a powder and the hexane
was continuously evaporated from the polymerization z3ne.
The polymerization temperature was 70C, A copolymer
powder having a K value of 70 (determined in 5% strength
NaCl solution) and a particle diameter of from 0,1 to
4 mm was obtained. Aqueous solutions of the copoly-
mer were used as a hair strengthener,
EXAMPLE 12
Preparation of a copolymer of styrene and acrylic acid
1,500 g of nylon granules of particle diameterfrom 1 to 2 mm were introduced into the apparatus9
described in Example 1, for the batchwise preparation of
polymer powders, The oilbath was brought to 90C,
A solution of 600 g of styrene and 200 g of acrylic acid
in 2,5 liters of cyclohexane, and a solution of 20 g of
6~
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an initiator, namely lauroyl peroxide 9 in 250 ml of
cyclohexane were then combined, in a volumetric flow
ratio of 10:1, by means of a static mixer, and the mix-
ture was sprayed, over 4 hours, onto the agitated solid-
particle bed~ During the polymerization, the material
in the polymerization zone was maintained in the form of
a powder and the solvent was removed from the polymeri-
zation zone by evaporation. The polymerization
temperature was 85C. A copolymer having a K value
lo of 50 and an acid number of 350 was obtainedO The
particle diameter of the copolymer was from 0.5 to 3 mm.
The copolymer was useful as a binder for road-marking
processes, and as a metal-coating agent.
EXAMPLE 13
- Preparation of polyacrylic acid
1,500 g of nylon granules of particle diameter
from 1 to 2 mm were introduced into the apparatus des-
cribed in Example 1 and the oilbath was brought -to 90C.
A solution of 1,200 g of acrylic acid in 4 liters of
cyclohexane was then combined with a solution of 10 g of
initiator, namely tert.-butyl perpivalate~ in 400 ml of
cyclohexane, in a volumetric flow ratio of 10:1, by
means of a s-tatic mixer, and the mixture of acrylic acid
and polymerization initiator in cyclohexane was sprayed,
over 5 hours, onto the constantly circulated solid-
particle bed. The polymerization temperature was
~0C. During the pol~merization, the sol~ent was
continuously evapora-ted from the polymerization zone.
Polyacrylic acid having a K value of 105 (de-termined in
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5% strength NaC1 solution) and a particle diameter of
from 0.5 to 3 mm was ob-tained. The polymer was use-
ful as a thickener in print pastes.
EXAMPLE 14
Preparation of ammonium polyacrylate
1,500 g of nylon granules of particle diameter
from l to 2 mm were introduced into the apparatus des-
cribed in Example l and the oilbath was brought to 75C.
A solution of 1,000 g of acrylic acid in 3,000 g of
methyl tert.-butyl ether and a sol.ution of 16.6 g of an
initiator9 namely bis-(4-tert.-butylcyclohexyl) peroxy-
dicarbonate, in 500 ml of methyl tert.-butyl ether were
then combined, in a volumetric flow ratio of lO:l,bymeans
of astatic mixer and the resulting mixturewasspraye~ over
5 hours, onto the constantly circulating solid-particle
bed. The polymerization temperature was 75C. An
atmosphere of ammonia was maintained in the reactor.
During the polymerization, the reaction mixture was main-
tained in the form of a pcwder and the methyl tert.-butyl
ether was removed completely, as vapor, from the reaction
chamber, due to the heat of polymerization, the heat of
neutralization and the energy introduced by stirring.
Ammonium polyacrylate having a
K value of 127.3 (measured on an O.l~o strength solution
in 5% strength NaCl solution) and a particle dlameter of
from 0.1 to 2 mm was obtainedO
