Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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HOECHST ARTIENGESELLSC~AFT HOE 93/F 381 Dr. RD/wo
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Description
Proce~e for preparing ~inely divided polyacrylonitrile
The preeent invention relates to a process for preparing
finely divided homopolymers or copolymers containing
recurring acrylonitrile and/or methacrylonitrile unit~.
It is known that acrylonitrile can be polymeri~ed by
various proce~ses. For acrylic fiber~, acrylonitrile is
usually polymerized by solution or suspen~ion-precipi~
tation polymerization. In the su~pension-procipitation
polymerization, the polymer is u~ually obtained as a
finely divided suspenaion which can be filtered off,
washed and dried.
The particle size of acrylonitrile polymers i~ usually
characterized by a so-called D value. The diameter D(p)
at the percentile point p and the median value D(50 %) is
defined as follows: ~;
Starting out from the volume distribution
Dmax
V = J v(Di)dD
Dmin
the diameter D(p) i~ given at the point where ;~
D1 = D (~
f
J v(Di)dD p * V.
D1 = D(O %)
V i~ the total volume of the particles
Di is the diameter o~ the individual particles
v(D~ the volume of the individual particles
Dmin = D(O %) i8 the ~mallest particle diameter
-
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DmaX = D(100 %) ie the largest part~cle diameter
p is the percentile value. -
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This determines a mean particle diameter, where the
maximum particle diameter, derived from the volume
distribution function, which would l~ad to X % passing a
sieve ic the eo-called AX value. Thus, for example, for
p - 50 % this means that all particle~ having a diameter
D c D(50 %) together make up 50 % of the total volume
(z median diameter). (T. Allen "Particle Size Measurement
Chapman & Hall ~td., London Mal~ern Instrument~ Ltd.
"System 3601 Usermanual" Spring Lane South, Worc
WR 14 1 AQ, England; p. 5.1 ff.)
. . ; . '
For suspension-precipitation polymerizations carried out
according to the prior art, the D50 % value of the
particle size i~ usually not below 40 ~m.
Further acrylonitrile polymers known p~r ~e are t~e SAN,
ABS and NBR copolymer~ which are generally prepared by
emulaion poly~erization. Thi~ gives a latex which may
have to first be broken for further processing. The
individual particles of thi~ latex are u~ually not larger
than 0.08 ~m but have an irregular particle geometry. The
acrylonitrile content in the~e known copolymers i~ below
50 % by weight.
.
The proce~es hitherto known for preparing
poly(meth)acrylonitrile having a particle ~ize of less
than 10 ~m are compl~cated and are hardly economically
~uitable for the preparaton of relatively large to
industrial amount~. Thus, JP-A-01/043531 de~cribe~ a ~;
proces~ in which a coar~ely particulate polyacrylonitrile
polymelr containing more than 80 % by weight of
acrylonitrile i~ dissolved in a ~uitable solvent and is
~ubsequently precipitated again. Besides this precipita-
tion process, DE-A-3,940,781 de~cribels a mechanical
proce~ in which a coarsely particulate polyacrylonitrile
polymer is finely milled together with up to 94 % by
: ~ ' ' : ~ . . :
: . .
-- 3
weight of acrylonitrile in ~pacial mills, for example a
fluidized-bed counter-jet mill or a ~tirred ball mill
(cf. al~o Ullmann's Encyclopedia of Indu~trial ~hemietry,
5th Edition, Volume B2, 5-20 to 34, VCH-Verlag, Weinheim
1988). Both known processe~ require complicated appa-
ratus.
,
Experiments have shown that the particle~ of the poly-
acrylonitrile milled in accordance with DE-A-3,940,781
res~hle squashed platelet~ on microecopic examination,
and that the particles of the polyacrylonitrile precipi-
tated in accordance with JP-A-01/043531, l~kewi~e on
microscopic exam$nation, have a tattered and eplit
surface structure.
JP-A-04/261404 describe~ a process $or preparing poly-
acrylonitrile particles having a mean diameter of
1:10 ~m. For this purpose, the polymerization mixture
comprising acrylonitrile monomer, di~persion stabilizer,
a hydrophilic and a hydrophobic solvent is polymerized
with ~haking at 65~.
20 JP-A-02/307909 discloses rod-shaped poly(meth)acrylo-
nitrile particles. The preparation of the rod-~haped
particle~ is carried out by polymerization of a suspen-
sion of the monomers, previously homogenized by stirring,
in a water/polyvinyl alcohol ~olvent mixture.
25 Furthermore, it i8 known from Ullmann, Volume 19, (1980),
pp. 130 ff. that alteration of the stirring ~peed during
the suspeneion-precipitation polymerization can influence
the particle size of the polymer~ formed. By mean~ of the
above-described measure, the particle ~ize~ can be varied
30 within a range from 1000 to 200 ~m. It is not po~eible to
extrapolate the D50 % value of the particle sizes to
below 10 ~m as a function of the ~tirring speed; particle
~ize~ below 200 ~m cannot be produced u3ing the usually
achievable stirring speeds.
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It ie therefore an object of the invention to develop a
~imple and a~ economical a~ po~ i~le process for prepa-
ring poly(meth)acrylonitrile, in which the polymer is
obtained after polymerization directly in the form of
small particle~ and in which the particle diameters have
a D50 % value of les~ than 10 ~m.
. .
It has now been found that it is po~ible to prepare a
poly(meth)acrylonitrile powder having a D50 % value of
less than 10 ~m if in polymerization the total monomer
concentration iB reduced below a range customary for the
polymerization of acrylonitrile and at the same time high
shear force~ act on the polymerization mixture.
, .
The invention accordingly provides a procesc for prepa-
ring homopolymers or copolymer~ containing at leaRt 50 %
by weight of recurri~g acrylonitrile and/or methacrylo-
nitrile unit~, which comprices:
a) dissolving and/or su~pending and/or emul~ifying
and/or dispersing the monomers in one or more
liquids which are inert under the reaction condi-
tions, where
b) the sum of the monomer concentrationc at the begin-
ning and during the polymerization is less than 10 %
by weight,
c) high ~hear forces acting on the polymerization
mixture prior to and during the polymerization eo
that the resulting homopolymer or copolymer
particles have a D50 % value of le~8 than 10 ~m and
d) carrying out the polymerization in a known manner by
addition of a polymerization initiator.
The low monomer concentration at the beginning and during
the polymerization (le~ than 10 % by weight, baaed on
the polymerization mixture) is an unuQual range for those
ckilled in the art of polymerization, ~ince the reaction
rate in a polymerization having an initial monomer
concentration of le~s than 10 % by weight is normally
very low and as a re~ult only low yield~ and ~pace-time
S 3 ~
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conver~ions can be achieved.
A~ has been surpri~ingly found, action of high shear
forces on the polymerization mixture during the
polymerization and copolymerization of acrylonitrile
and/or methacrylonitrile gives unexpectedly high reaction
ratee and space-time yields. Furthermore, the particle
size distribution can be varied and set within a wide
range by the measures of the invention. The preferred
D50 % value of the particle si~e of the finely divided
polyacrylonitrile i~ less than 10 ~m and greater than
0.1 ~m. By mean~ of the particle size, further specific
propertie~ such as, for example the rheology and the
external and internal surface ar0a, can, lf desired, be
influenced and altered in a targeted mann0r.
The acrylonitrile and/or methacrylonitrile polymers
prepared using the proce~s of the invention preferably
contain 70 % by weight of recurring acrylonitrile and/or
methacrylonitrile units. Furthermore, up to 30 % by
weight of one or more monomers capable of
copolymerization can be added to the acrylonitrile and/or
methacrylonitrile. Partlcular preference is given to
poly(meth)acrylonitrile polymer~ containing at least 90 %
by weight of recurring acrylonitrile and/or methacrylo-
nitrile units.
Examples of monomers capable of copolymerization are
acrylic esters or methacrylic ester~ of Cl^C22-alcohols,
e.g. methyl acrylate, methyl methacrylate, butyl
methacrylate, octyl methacrylate, ethyl acrylate,
i~obutyl acrylate, (meth)acrylic e~ters of perfluorinated
Cl-C22-alcohols; vinyl aromatics having up to 20 carbon
atom~, e.g. styrene, vinyltoluene; the esters of maleic
acid and fumaric acid with C1-C22-alcohol~; vinyl
chloride, vinyl acetate, ethylene and butadiene. Prefe-
rence is given to methyl acrylate.
Furthermore, it i8 pos~ible to u~e, for example,
.: .. . ~ .
`3 ~3 2
.:
un~aturated carboxylic, sulfonic and phosphonic acids and
their ester~ and salts as comonomers, examples being
acrylic acid, crotonic acid, itaconic acid, vinyl~ulfonic
acid, (meth)acrylosulfonic acid, styrenesulfonia acid,
acrylamidomethylpropanesulfonic acid, vinylpho~phonic
acid and ester~ thereof.
The suitable comonomers likewi~e include unsaturated
primary, secondary and/sr tertiary amines, such as
dimethylaminoneopentylmethacrylate,dimethylaminomethyl-
neopentyl acrylate, 2-N-morpholinoethyl methacrylate,
2-N-morpholinoethyl acrylate, or amides of acrylic or
methacrylic acid, such as acrylamide, dimethyl-
methacrylamide or methylbutylacrylamide.
'
In addition, it is also possible to use other functional
monomers which can be copolymerized with acrylonitrile
and/or methacrylonitrile. The functional monomers can
contain hydroxy, silane or epoxy groups. Examples of
the~e are vinyltrimethoxysilane, vinyltributoxysilane,
methacryloxypropyltrimethoxysilane, vinyltris(methoxy-
ethoxy)silane, vinyltriacetoxysilane, hydroxyethylmethacrylate, hydroxybutyl methacrylate, glycidyl
acrylate, glycidyl methacrylate or 2-hydroxyethyl
acrylate.
' ' :' '~
By means of the selection of the monomer~ to be used,
properties such as the glass transition temperature,
hardness and brittleness can be influenced.
:'
The term polymerization refer~, in particular, to preci-
pitation polymerizations in which the monomers are
dis~olved and/or suspended and/or emulsified and/or
dispersed beforehand in one or more liquids inert in
respect of the monomer and polymer. The proce~s of the
invention is preferably carried out by the suspension-
precipitation polymerization method.
The shear force nece~sary during polymerization i~
usually generated by one or more ~tirrers and/or other
di~persing devices which generate high shear and which
. .
9 ~
-- 7
can be u~ed ~imultaneou~ly and/or ~uccessively. Examples
of these are propeller, impeller, turbine, guide jet,
inclined blade, toothed disc (di~solver) or pinned di~c
(dissolver) stirrer, with and without baffles. It is
likewi~e po~ible to use all types of static and dynamic
mixers and also jet mixers as disper~ing devices. Jet
mixers mean such mixers which mix the polymerization
mixtures by passage through a nozzle. Preference is given
to stirrer~ using the rotor/stator principle ~uch a~
stirrers of the Ultra-Turrax (from Janke & Runkel,
Staufen, Germany) type or stirrers of the Pentax (from
Bran & Lubbe, Hamburg, Germany) type.
Furthermore, the di~persion can al~o be carried out using
devices built into the reactor and/or by (forced) circu-
lation (inline) outside the reactor.
The polymerization reaction can be carried out batchwiee,semi-continuou~ly or continuously.
Suitable reactore for the continuous polymerization
process are, for example, the continuous stirred tank
reactor, a cascade comprising from 2 to 4 reactors, the
tube reactor or the loop reactor or any desired combina-
tion of the specified reactors.
Suitable liquids which are inert under the reaction
conditions are protic and/or aprotic solvents and/or non-
solvents and mixtures thereof. Suitable aprotic solventsare either nonpolar ones, such as aliphatic and aromatic
hydrocarbons, or polar ones such as halogenated hydro-
carbons, dimethylformamide, dimethyl sulfoxide, dimethyl-
acetamide and acetonitrile. Suitable protic reaction
media are, for example, water and alcohol~.
The total monomer concentration at the beginning and
during the polymerization is at most 10 % by weight,
preferably from 1 to 10 ~ by weight, paticularly prefe-
rably from 3 to 8 % by weight.
The molecular weight of the poly(meth)acrylic pol~mers
... . .
: . . . . .. .
.
.
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can be set in a conventional manner by the selection of
the radical initiator and by polymerization variables
known to thoee skilled in the art, euch as initiator
concentration and/or polymerization temperature. The
molecular weight Mw (weight average) of the
poly(meth)acrylonitrile polymere prepared by the process
of the invention is ueually from 3 x 104 to
8 x 105 g~mol, preferably from 5 x 104 to 4.5 x 105 g/mol.
If deeired, the molecular weight can be regulated by
meane o~ a chain regulator euch ae 2-mercaptoethanol. The
molecular weight Mw ie determined by the method of
Fikentscher (Makromol. Chem. 57 1962, 52) using the
relationehip
[~] = 1.78 x 10-4 x MW0.78
where ~ ie the viecoeity nu~ber (intrineic viecosity).
Polymerization initiatore which can be ueed are either
water-eoluble compounde euch ae, for example, H2O2,
potaeeium peroxodieulfate and organic azo and peroxo
compounde, or compounde which are sparingly eoluble in
water euch ae, for example, azobieieobutyronitrile or
other azo and peroxo compounde. The particularly
preferred radical initiator ie the redox eyetem potaeeium
peroxodieulfate and eodium bisulfite.
An emuleifier can be additionally added to the
polymerization mixture. By thie meane, the particle sizs
of the polymer can be further reduced or the polymer can
be given epecific propertiee such ae, for example, a
particularly good euitability for cathodically depoei-
table coating compoeitione.
Suitable emuleifiere are:
cationic surfactants euch ae cetylamine hydrochloride and
ealte of other fatty aminee with etrong acide;
non-ionogenic emuleifiere euch as fatty alcohol ethoxy-
lates and alkylphenol ethoxylatee euch ae, for example,
r~
_ 9 _ : ~
the Genapol grades (Hoech~t AG); anionic ~urfactants
~uch as sodium lauryl sulfate and other alkyl sulfate~
and alkylbenzenesulfonates.
The polymerization can also be carried out using protec-
tive collo$d~ as dispersants. Suitable dispersants are,
for example, starch, sodium salt of carboxymethyl-
cellulose, methylcellulose, polyvinyl alcohol or
partially saponified polyvinyl acetate.
The reaction temperature for the polymerization is
usually 30-75C, preferably 40-60C; the polymerization
time is generally between 30 minutes and 5 hours and i8
dependent on the reaction procedure or polymerizatio~
temperature and also on the monomers, the solvent, the
initiator substances and the polymerization procese
selected in the particular case.
The polyacrylonitrile suspension obtained can be freed of
monomers after polymerization, for example by distilla-
tion. Before or subsequent to the removal of monomerc,
the liquid phase can be mostly removed, for example by
filtration or by means of a centrifuge. By waehing with
water and filtering or centrifuging again, the poly~er
suspen~ion can be freed of interfering salts and other
residual materials. Subsequently, the finely divided
poly(meth)acrylonitrile polymer ~till containing residual
water can be dried, with care having to be taken to
ensure that the particle~ do not agglomerate. Suitable
driers are, for example, ~pray driers and rotary di~k
atomization driers.
The particle surface of the almost round particles can,
on microscopic examination, be described as a compara~
tively raspberry-like ~tructure in which the ~urface of
the almost round polymer particle ha~ sitting on it
further round polymer particles. As a re~ult, the polymer
particle i~, in contrast to milled or precipitated
polymer~, almost round (spherical geometry) and has a
~: .'
a J 9 2
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large specific surface area.
The finely divided polymer is auitable, for example, as
pigmenting agent and organic filler. Particularly a~
pigment eubstitute in place of titanium dioxide in
electrophoretic surface coatings of automobile or indus-
trial finishe~, the polymer ha~ many possible applica-
tion~. In addition, the finely di~ided polymer of the
invention can be ueed as matting agent and colorable
pigment in surface coating~, pla~tics, Çibers, films,
paper and cardboard. The polymer haR a ~ery high internal
and external sur~ace area. Depending on the particle
size, it absorbs from over 5 times to over 10 times its
weight of water and other liquids without losing its
paste-like aggregated state in which it iR firm enough to
be cut.
,:
The large surface area also offers increa~ed reactivity
for chemical reactions on the polymer grain, for example
gases or liquids can be adsorbed.
The good liquid absorption and ~torage capacity of the
polymer can be exploited in use as adsorbent and bind~r.
It can also be used as thixotrope and thick~ner in
surface coatings, plastics or the like.
In addition, the polymer can be u~ed as raw material for
(carbon)microbeads, as filler for liquid chromatography
or ion exchange columns, as reinforcing material and
filler for polymers or as starting material for polymsr-
analogou~ reaction~. Likewise, it can al~o be used as
starting material for fibers, film~ and mzmbranes.
The following working example~ illustrate the present
invention without limiting it.
Examples~
In the following examples, the particle size distribu-
tions are mea~ured using a Malvern particle sizer model
3600. ~-~
Initiation of polymerization wa~ carried out in the
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--` hl3~i 197
examples described below by addition of the ~olutions I
and II.
Solution I wa~ prepared from 50 ml of di~tilled water and
0.72 g of pota~ium peroxodi~ulfate and solution II was
prepared from 50 ml of di~tilled water and 2.88 g of
sodium bi~ulfite.
Example 1
(Acrylonitrile polymerization in aqueous medium: batch-
wise method)
A reaction ve3sel was initially charged with:
1520 ml of distilled water,
180 g of distilled acrylonitrile,
3.6 mg of Mohr's salt,
1.3 ml of 99 % strength formic acid.
After passing through nitrogen and set~ing the tempera-
ture to 55C, the polymerization wa~ initiated by
addition of the solutions I and II and the reaction
mixture was dispersed by means of a Ultra-Turrax stirrer
at about 10,000 revolutions per minute.
After the polymerization wa~ complete, the water and
unreacted monomer were separated off. Washing twice with
distilled water gave a polymer suspenaion which ha~ a
conductivity of le~s than 10 ~S/cm (measured ae a 10 %
strength suQpension in di~tilled water having an
intrinsic conductivity of at most 0.1 ~S/cm) and who~e
properties are shown in Table 1. The yield o~ polymer wa~
79.3 % of theory.
Example 2 to Example 4
The experiment~ were carried out as described in Example
1. Both the amounta u~ed and the re~ults are shown in
Table 1.
Example 5
The experiment wa~ sarried out as described in Example 1.
....... . . .. . . . . .
9 2
- L2 -
However, the stirrer used wa~ a di3~01ver ~tirrer having
a diameter of 150 mm and operating at 1500 revolution~
per minute. The results are shown in Table 1.
Example 6
The experiment was carried out a~ described in Example 1.
However, the etirrer used in the reactor was a propeller
stirrer having a diameter of 80 mm and operat~ng at 500
revolutlons per minute. The reaction mixture was
disper~ed by pumped circulation of the reaction mixture
through a flow-through chamber ~itted with an Ultra-
Turrax etirrer connected inline, the ~tirrer being
operated at about 10,000 rpm. The pumped circulation rate
was about 1,800 mg/min. The resulte are ehown in Table 1.
Example 7
(Semi-continous feed stream addition method)
.~ ~ ;. -:
The amounts used correspond to the amounts in Example 1.
However, only half the reaction mixture was initlally
.
charged and dispersed by means of an Ultra-Turrax
stirrer at about 10,000 revolution~ per minute. After
initiation with 25 ml of each of the solution~ I and II,
the remaining solutions were simultaneously metered into
the initial mixture over a period of one hour. The
results are shown in Table 1.
Example 8
(Continuous polymerization)
The amount~ used correspond to the amounts in Example 1.
1700 ml of the reaction mixture were initially charged
and di~persed by means of an Ultra-Turrax stirrer at
about 10,000 revolutions per minute. However, after
initiation with 50 ml of each of solutions I and II,
50 ml/h of the solutions I and II and also 1700 g/h of
the reaction mixture as was also initially charged at the
beginning of the reaction were simultaneously metered
into the initial mixture and a product stream of 1800 g
~135~2
- 13 -
per hour wae continuously taken out. After establishment
of equilibrium, sampling was commenced. The results are
shown in Table 1.
Example 9
The experiment was carried out as described in Example 1.
However, 5.4 g of the emulsifier Genapol GX 110 were
additionally added to the reaction mixture. The reeults
of the experiment axe shown in Table 1.
Example 10
A reaction vessel was initially charged with~
1500 ml of distilled water,
70 g of distilled acrylonitrile.
After passing through nitrogen and setting the tempera-
ture to 70C, lnltiation was carried out uslng 1.5 g of
azobieisobutyronitrile (AIBN) diesolved in 5 ml of
acrylonitrlle. Durlng the entire polymerization, the
reaction mlxture wa~ di~persed by mean~ of an Ultra-
Turrax stlrrer at about 10,000 revolutions per mlnute.
After a reaction time of 2 hours, the partlcle dlameter
(D50% value) was 5.50 ~m and the yield was 38.3 % of
theory.
Comparative Example 1:
The experiment wae carried out a~ described in Example 1.
However, the stirrer used was a propeller ~tirrer
(without baffles) having a diameter of 150 mm and opera~
ting at 1500 revolutions per minute. The results are
~hown in Tabls 1.
Comparative Example 2~
The experiment was carried out as described in Example 1.
Howevsr, the amount of monomer used wa~ 337.5 g. The
reaction mixture was dispersed by means of an
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Ultra-Turrax etirrer at about 10,000 revolutions per :
minute. The re~ults are shown in Table 1. ~ ~
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