Note: Descriptions are shown in the official language in which they were submitted.
CA 02883037 2015-02-25
Finely divided particles of core-shell structure
Description
The present invention relates to a process for producing finely divided
particles of core-shell
structure where the shell comprises at least one polymer. The invention also
relates to finely
divided particles of core-shell structure which are obtainable by this
process.
The controlled formation and structurization of finely divided composited
particles, i.e.,
particles having a multiphasic morphology, especially particles of core-shell
structure or core-
shell morphology, is of particular interest in order that particles having
specific properties
may be produced for highly specialized applications in a controlled manner.
Coated finely
divided particles of core-shell structure are interesting for numerous
applications, for example
in dye compositions or as catalysts. The polymer coating prevents the
agglomeration of the
particles, which leads to higher color intensity or improved catalyst
performance. In the
medical field of application, marker substances are polymer coated in order
that deleterious
effects of the particles on the organism may be prevented. The polymer coating
can
furthermore be used to protect the core material from external influences, for
example
corrosion, oxidation, reduction, water and so on. Properties such as for
example the
conductivity of coated particles can also be modified. Possibilities here are
for instance finely
divided particles of core-shell structure as hybrid materials for printed
electronics consisting
of conducting or semiconducting polymers with conducting or semiconducting
inorganic
particles. This results in a wide field of utility for finely divided
particles of core-shell
structure in optical, electronic, chemical, biotechnological and medical
systems.
Numerous processes for producing composite particles are known from the prior
art. These
include more particularly the processes in the liquid phase such as stepwise
emulsion
polymerization, emulsion polymerization in a suspension of nonpolymerizable
particles or in
an emulsion of nonpolymerizable droplets, microencapsulation by coacervation
and the like
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and also processes in the gas phase, for example photo-induced or chemically
induced gas
phase deposition.
B. Zhang etal., J. Nanopart. Res 2008, 10, 173-178, describe the coating of
sodium chloride
nanoparticles by photoinduced chemical gas phase deposition; A. M. Boies et
al.,
Nanotechnology 2009, 20, 29, 295604, describe the production of inorganic core-
shell
particles by chemical gas phase deposition.
J. F. Widmann et al., J. Colloid Interface Sci. 1998, 199, 197-205, describe a
process whereby
an isolated microparticle is captured in an electrodynamic trap and brought
into contact with a
monomer droplet. The resulting liquid nanoparticle coating is polymerized
photochemically.
The prior art processes for producing finely divided composited particles have
a number of
disadvantages. First, the composite particles are largely very inhomogeneous,
i.e., particle size
distribution is broad, particle shape is nonuniform or particle composition is
nonuniform.
Many finely divided composited particles exhibit addition structures only and
not a
pronounced core-shell morphology. Moreover, only certain particle size ranges
are achievable
with existing processes, and small particles are only obtainable in many
existing processes to
a limited extent, if at all.
Existing gas phase processes for producing core-shell particles are usually
limited to certain
particle-monomer combinations. Liquid phase processes additionally have the
disadvantage of
using emulsifiers, which are undesired for many applications and frequently
cannot be
removed. In addition, many existing processes for producing finely divided
composited
particles are unsuitable for large scale technical use because of their slow
throughput rate.
The present invention has for its object to provide a process for producing
finely divided core-
shell particles which overcomes the disadvantages of the prior art. More
particularly, the
process shall afford a high throughput, shall eliminate the need to use
surface-active
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substances such as emulsifiers and surfactants, and shall be implementable in
respect of a very
large number of core and monomer materials.
We have found that this object is achieved, surprisingly, by a process for
producing finely
divided particles of core-shell structure where the shell comprises at least
one polymer when
the process comprises the here and hereinbelow more particularly elucidated
steps i. to iv. and
wherein two oppositely charged aerosol streams are mixed with each other, the
first aerosol
stream comprising polymerizable monomers and the second aerosol stream
comprising solid
particles, and then a polymerization is induced photochemically. This gives
particles of core-
shell structure wherein the core is formed by the particles of the second
aerosol stream and a
polymeric shell is formed by the polymerized monomers of the first aerosol
stream.
The invention accordingly provides the here and hereinafter described process
comprising the
steps of:
i. providing a first aerosol stream of droplets in a carrier gas stream
wherein the droplets
comprise at least one monomer and charging droplets of the first aerosol with
electric
charge;
ii. providing a second aerosol stream of solid particles in a carrier gas
stream and charging
the solid particles of the aerosol with an electric charge opposite to the
electric charge
on the droplets of the first aerosol stream;
iii. mixing the first aerosol stream with the second aerosol stream to form a
mixed aerosol
stream;
iv. initiating a polymerization of the monomers by irradiating this mixed
aerosol stream
with electromagnetic radiation.
Advantages of the process according to the present invention are, first, a
high purity for the
product, since no surface-active substances such as emulsifiers or surfactants
have to be
added. Nor is it necessary to add a solvent. Nor is it necessary to add a
photoinitiator to the
monomers when the particles of the second aerosol stream act as a
photoinitiator or high-
energy radiation is used. The process of the present invention affords the
simultaneous
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coating of a multiplicity of particles. The process can be applied to a
multiplicity of core
particles that are solid, since it is a purely physical process to charge and
coagulate oppositely
charged droplets and particles. The finely divided core-shell particles
obtainable according to
the present invention have a particularly uniform core-shell structure. A
further advantage of
the process according to the present invention is that the like electrostatic
charges on the solid
particles and droplets prevent particles and droplets coagulating with one
another, i.e., within
the two aerosol streams. As a result, the process of the present invention
provides a narrower
particle size distribution and hence better reproducibility of the core-shell
particles obtained.
A further advantage of the process according to the present invention over
processes
involving thermally induced polymerization is that heating can be dispensed
with. The
necessary heating during thermally induced polymerization causes some of the
monomers to
evaporate, so particle diameter and shell thickness adjustment is complicated
and often
irreproducible and may only result in incomplete coating being achieved. By
contrast, using
the process of the present invention the thickness of the polymer shell is
easy to control in a
specific manner by varying the droplet size in the first aerosol stream and
via the ratio of mass
flows in the aerosol streams.
A person skilled in the art is able to adjust the structure of the finely
divided core-shell
particles obtained after the polymerization to the desired result by varying
the process
parameters such as droplet size for the first aerosol stream, number of
charges on the droplets
and/or particles, particle and droplet concentrations, mixing zone geometry
and length,
residence time in any unilluminated residence zone.
According to the present invention, the particles produced comprise at least
one polymer
which, for the purposes of the present invention, is to be understood as
meaning a
homopolymer and/or copolymer. The term "homopolymers" is to be understood as
meaning a
polymer polymerized from the same monomers. The term "copolymer" is to be
understood as
meaning a polymer polymerized from two or more different monomers.
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In general, the first aerosol stream in the process of the present invention
can utilize any
monomer that is polymerizable by exposure to electromagnetic radiation.
Olefinically
unsaturated monomers are concerned in particular as well as cyclic monomers
amenable to a
photochemically induced ring-opening polymerization.
The monomers of the first aerosol stream may be neutral, acidic, basic or
cationic for
example.
The monomers are preferably selected among olefinically unsaturated monomers,
i.e.,
monomers having at least one, e.g., one, two, three or four, C=C double bonds,
in which case
particular preference is given to monomers of this type where the C=C double
bond are in the
form of a vinylic double bond, i.e., a monosubstituted double bond, or a
vinylidene double
bond, i.e., a disubstituted double bond where the two substituents are
attached to the same
carbon atom involved in the C=C double bond. Preference is given especially to
olefinically
unsaturated monomers where the double bond is in conjugation with an
unpolymerizable
double bond, for example in conjugation with a carbonyl group, a nitrile group
or an aromatic
ring, for example a benzene ring, imidazole ring or a pyridine ring.
More preferably, the at least one monomer is selected among monoolefinically
unsaturated
monomers and especially among mixtures of at least one monoolefinically
unsaturated
monomer with at least one polyolefinically unsaturated monomer.
In a preferred embodiment of the present invention, the first aerosol stream
used in the
process of the present invention in addition to the at least one monomer
comprises at least one
polyolefinically unsaturated monomer (crosslinker).
Polyolefinically unsaturated monomers in the polymerization reaction of the
provided
monomers are effective in crosslinking and hence increasing the molecular
weight of the
polymers obtained. The at least one crosslinker is used for example in an
amount of 1 to 80%
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by weight, preferably of 2 to 20% by weight and more preferably 3 to 15% by
weight, all
based on the total amount of olefinically unsaturated monomers.
In a further preferred embodiment of the present invention, the at least one
monomer used in
the first aerosol stream of the process according to the present invention
comprises essentially
exclusively at least one polyolefinically unsaturated monomer (crosslinker).
In this
embodiment, the at least one polyolefmically unsaturated monomer is generally
used in an
amount of 80 to 100% by weight, preferably in an amount of 90 to 100% by
weight and more
preferably in an amount of 97 to 100% by weight, all based on the total amount
of olefinically
unsaturated monomers.
More preferably, at least 90% by weight of the monomers in the aerosol stream
are selected
among neutral olefinically unsaturated monomers.
Neutral monoolefinically unsaturated monomers suitable for the purposes of the
present
invention are generally selected among monoolefinically unsaturated C3-C6
monocarboxylic
acids, monoolefinically unsaturated C4-C6 dicarboxylic acids, esters of
monoolefinically
unsaturated C3-C6 monocarboxylic acids, esters of monoolefinically unsaturated
C4-C6
dicarboxylic acids, amides of monoolefinically unsaturated C3-C6
monocarboxylic acids, N-
vinylamides, N-vinyllactams, vinylaromatics, vinyl ethers, vinyl, allyl and
methallyl esters,
monoolefinically unsaturated nitriles, a-olefins, monoolefinically unsaturated
sulfonic acids,
monoolefinically unsaturated phosphonic acids and monoolefinically unsaturated
phosphoric
half-esters, especially among neutral monoethylenically unsaturated monomers
from the
groups of esters of monoolefinically unsaturated C3-C6 monocarboxylic acids,
esters of
monoolefinically unsaturated C4-C6 dicarboxylic acids, amides of
monoolefinically
unsaturated C3-C6 monocarboxylic acids, ethylenically unsaturated nitriles,
vinyl ethers and
mixtures thereof with one or more acidic monomers such as monoolefinically
unsaturated C3-
C6 monocarboxylic acids, monoolefinically unsaturated C4-C6 dicarboxylic
acids,
monoolefinically unsaturated sulfonic acids, monoolefinically unsaturated
phosphonic acids
and monoolefinically unsaturated phosphoric half-esters.
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Examples of neutral monoolefinically unsaturated monomers suitable for the
purposes of the
present invention are particularly the monomers of the following groups M1 to
M12,
especially those of groups Ml, M2, M4, M6, M7, M8, M9, M10 and M12,
specifically those
of groups Ml, M2, M6, M7, M8, M9 and M10:
M1 esters of monoolefinically unsaturated C3-C6 monocarboxylic acids
with C1-C20
alkanols, C5-C8 cycloalkanols, phenyl-Ci-C4-alkanols or phenoxy-Ci-C4-
alkanols,
especially the aforementioned esters of acrylic acid and also the
aforementioned esters
of methacrylic acid, for example methyl acrylate, ethyl acrylate, n-propyl
acrylate,
isopropyl acrylate, n-butyl acrylate, 2-butyl acrylate, isobutyl acrylate,
tert-butyl
acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, 3-propylheptyl acrylate,
decyl acrylate,
lauryl acrylate, stearyl acrylate, cyclohexyl acrylate, benzyl acrylate, 2-
phenylethyl
acrylate, 1-phenylethyl acrylate, 2-phenoxyethyl acrylate, and also the esters
of
methacrylic acid such as methyl methacrylate, ethyl methacrylate, n-propyl
methacrylate, isopropyl methacrylate, n-butyl methacrylate, 2-butyl
methacrylate,
isobutyl methacrylate, tert-butyl methacrylate, n-hexyl methacrylate, 2-
ethylhexyl
methacrylate, decyl methacrylate, lauryl methacrylate, stearyl methacrylate,
cyclohexyl
methacrylate, benzyl methacrylate, 2-phenylethyl methacrylate, 1-phenylethyl
methacrylate and 2-phenoxyethyl methacrylate;
M2 diesters of monoolefinically unsaturated C4-C6 dicarboxylic acids with C1-
C20 alkanols,
C5-C8 cycloalkanols, phenyl-Ci-C4-alkanols or phenoxy-Ci-C4-alkanols,
especially the
aforementioned diesters of maleic acid and the diesters of fumaric acid,
especially di-
C1-C20-alkyl maleates and di-C1-C20-alkyl fumarates such as dimethyl maleate,
diethyl
maleate, di-n-butyl maleate, dimethyl fumarate, diethyl fumarate and di-n-
butyl
fumarate;
M3 vinylaromatic hydrocarbons, for example styrene, vinyltoluenes, tert-
butylstyrene, a-
methylstyrene and the like, especially styrene;
M4 vinyl, allyl and methallyl esters of saturated aliphatic C2-C18
monocarboxylic acids, for
example vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl
hexanoate,
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vinyl 2-ethylhexanoate, vinyl laurate and vinyl stearate and also the
corresponding allyl
and methallyl esters, and
M5 a-olefins of 2 to 20 carbon atoms and cycloolefins of 5 to 10 carbon
atoms such as
ethene, propene, 1-butene, isobutene, 1-pentene, cyclopentene, cyclohexene and
cycloheptene;
M6 esters of monoolefinically unsaturated C3-C6 monocarboxylic acids
with polyether
monools, especially with CI-C20-alkyl poly-C2-C4-alkylene glycols,
specifically with
Ci-C20-alkyl polyethylene glycols, wherein the alkyl polyalkylene glycol
moiety
typically has a molecular weight in the range from 200 to 5000 g/mol (number
average),
especially the aforementioned esters of acrylic acid and also the
aforementioned esters
of methacrylic acid;
M7 monoolefinically unsaturated nitriles such as acrylonitrile or
methacrylonitrile,
M8 amides of the aforementioned monoolefinically unsaturated C3-C8
monocarboxylic
acids, especially acrylamide and methacrylamide,
M9 N-(C1-C20-alkyl)amides and N,N-di-(C1-C20-alkyl)amides of the
aforementioned
monoolefinically unsaturated C3-C8 monocarboxylic acids;
M10 hydroxyalkyl esters of the aforementioned monoolefinically unsaturated C3-
C8
monocarboxylic acids, e.g., hydroxyethyl acrylate, hydroxyethylmethacrylate,
2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxypropyl
methacrylate and
3-hydroxypropyl methacrylate;
Mll N-vinylamides of aliphatic C1-Cio carboxylic acids and N-vinyllactams such
as
N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone and N-vinyleaprolactam;
M12 vinyl ethers of C1-C20 alkanols such as methyl vinyl ether, ethyl vinyl
ether, isobutyl
vinyl ether, benzyl vinyl ether.
Examples of acidic monoolefinically unsaturated monomers suitable for the
purposes of the
present invention are particularly the monomers of the following groups M13 to
M17:
M13 monoolefinically unsaturated C3-C6 monocarboxylic acids such as acrylic
acid,
methacrylic acid, vinylpropionic acid and ethacrylic acid and monoolefinically
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unsaturated C4-C6dicarboxylic acids such as itaconic acid, maleic acid,
fumaric acid
and citraconic acid and also anhydrides thereof,
M14 monoolefinically unsaturated sulfonic acids where the sulfonic acid group
is attached to
an aliphatic hydrocarbon moiety, and salts thereof, such as vinylsulfonic
acid,
allylsulfonic acid, methallylsulfonic acid, 2-acrylamido-2-
methylpropanesulfonic acid,
2-methacrylamido-2-methylpropanesulfonic acid, 2-acrylamidoethanesulfonic
acid, 2-
methacrylamidoethanesulfonic acid, 2-acryloyloxyethanesulfonic acid, 2-
methacryloyloxyethanesulfonic acid, 3-acryloyloxypropanesulfonic acid and 2-
methacryloyloxypropanesulfonic acid and salts thereof,
M15 vinylaromatic sulfonic acids, i.e., monoolefinically unsaturated sulfonic
acids where the
sulfonic acid group is attached to an aromatic hydrocarbon moiety, especially
to a
phenyl ring, and salts thereof, for example styrenesulfonic acids such as 2-,
3- or 4-
vinylbenzenesulfonic acid and salts thereof,
MI6 monoolefinically unsaturated phosphonic acids where the phosphonic acid
group is
attached to an aliphatic hydrocarbon moiety, and salts thereof, such as
vinylphosphonic
acid, 2-acrylamido-2-methylpropanephosphonic acid, 2-methacrylamido-2-
methylpropanephosphonic acid, 2-acrylamidoethanephosphonic acid, 2-
methacrylamidoethanephosphonic acid, 2-acryloyloxyethanephosphonic acid, 2-
methacryloyloxyethanephosphonic acid, 3-acryloyloxypropanephosphonic acid and
2-
methacryloyloxypropanephosphonic acid and salts thereof,
M17 monoolefinically unsaturated phosphoric half-esters, especially the half-
esters of
phosphoric acid with hydroxy-C2-C4-alkyl acrylates and hydroxy-C2-C4-alkyl
methacrylates such as, for example, 2-acryloyloxyethyl phosphate,
2-methacryloyloxyethyl phosphate, 3-acryloyloxypropyl phosphate,
3-methacryloyloxypropyl phosphate, 4-acryloyloxybutyl phosphate and
4-methacryloyloxybutyl phosphate and salts thereof.
The monomers of the following groups M18 to M21 are examples of basic and
cationic
monoolefinically unsaturated monomers useful in the first aerosol stream of
the process
according to the present invention:
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M18 vinylheterocycles such as 2-vinylpyridine, 3-vinylpyridine, 4-
vinylpyridine and
N-vinylimidazole;
M19 quaternized vinylheterocycles such as 1-methy1-2-vinylpyridinium salts, 1-
methy1-2-
vinylpyridinium salts, 1-methy1-4-vinylpyridinium salts, and N-methyl-N-vinyl-
imidazolium salts, for example the chlorides or methosulfates;
M20 N,N-(di-CI-C10-alkyl amino)-C2-C4-alkyl amides and N,N-(di-CI-C10-
alkylamino)-C2-C4-
alkyl esters of the aforementioned monoolefinically unsaturated C3-C8
monocarboxylic
acids, e.g., 2-(N,N-dimethylamino)ethylacrylamide, 2-(N,N-dimethyl-
amino)ethylmethacrylamide, 2-(N,N-dimethylamino)propylacrylamide, 2-(N,N-
dimethylamino)propylmethacrylamide, 3-(N,N-dimethylamino)propylacrylamide, 3-
(N,N-dimethylamino)propylmethacrylamide, 2-(N,N-diethylamino)ethylacrylamide,
2-
(N,N-diethylamino)ethylmethacrylamide, 2-(N,N-diethylamino)propylacrylamide, 2-
(N,N-diethylamino)propylmethacrylamide, 3-(N,N-diethylamino)propylacrylamide,
3-
(N,N-diethylamino)propylmethacrylamide, 2-(N,N-dimethylamino)ethyl acrylate, 2-
(N,N-dimethylamino)ethyl methacrylate, 2-(N,N-dimethylamino)propyl acrylate, 2-
(N,N-dimethylamino)propyl methacrylate, 3-(N,N-dimethylamino)propyl acrylate,
3-
(N,N-dimethylamino)propyl methacrylate, 2-(N,N-diethylamino)ethyl acrylate, 2-
(N,N-
diethylamino)ethyl methacrylate, 2-(N,N-diethylamino)propyl acrylate, 2-(N,N-
diethylamino)propyl methacrylate, 3-(N,N-diethylamino)propyl acrylate and 3-
(N,N-
diethylamino)propyl methacrylate;
M21 N,N-(tri-C -C1 o-alkylammonium)-C2-C4-alkylamides and N,N-(tri-C -C 10-
alkyl-
ammonium)-C2-C4-alkyl esters of the aforementioned monoolefinically
unsaturated
C3-C8 monocarboxylic acids, e.g., 2-(N,N,N-trimethylammonium)ethylacrylamide,
2-(N,N,N-trimethylammonium)ethylmethacrylamide, 2-(N,N,N-trimethyl-
ammonium)propylacrylamide, 2-(N,N,N-trimethylammonium)propylmethacrylamide,
3-(N,N,N-trimethylammonium)propylacrylamide, 3-(N,N,N-
trimethylammonium)propylmethacrylamide, 2-(N,N,N-triethylammonium)ethyl-
acrylamide, 2-(N,N,N-triethylammonium)ethylmethacrylamide, 2-(N,N,N-triethyl-
ammonium)propylacrylamide, 2-(N,N,N-triethylammonium)propylmethacrylamide, 3-
CA 02883037 2015-02-25
(N,N,N-triethylammonium)propylacrylamide, 3-(N,N,N-triethylammonium)-
propylmethacrylamide, 2-(N,N,N-trimethylammonium)ethyl acrylate, 2-(N,N,N-
trimethylammonium)ethyl methacrylate, 2-(N,N,N-trimethylammonium)propyl
acrylate, 2-(N,N,N-trimethylammonium)propyl methacrylate, 3-(N,N,N-
trimethylammonium)propyl acrylate, 3-(N,N,N-trimethylammonium)propyl
methacrylate, 2-(N,N,N-triethylammonium)ethyl acrylate, 2-(N,N,N-
triethylammonium)ethyl methacrylate, 2-(N,N,N-triethylammonium)propyl
acrylate, 2-
(N,N,N-triethylammonium)propyl methacrylate, 3-(N,N,N-triethylammonium)propyl
acrylate and 3-(N,N,N-triethylammonium)propyl methacrylate, especially their
chlorides, methosulfates and ethosulfates.
Polyolefinically unsaturated compounds (crosslinkers) include for example
divinylbenzenes,
diesters and triesters of olefinically unsaturated carboxylic acids,
especially the bis- and
trisacrylates of diols or polyols having 3 or more OH groups, for example the
bisacrylates and
the bismethacrylates of ethylene glycol, diethylene glycol, triethylene
glycol, neopentyl
glycol or polyethylene glycols, 1,6-hexanediol diacrylate (HDDA), allyl
methacrylate (AMA)
and trimethylolpropane trimethacrylate (PMPTMA).
Useful monomers of the process of the present invention further include
saturated cyclic
compounds capable of being polymerized by a photochemically initiated ring-
opening
polymerization. Examples of monomers of this type are cyclic ethers, for
example epoxides,
oxetanes, furans and cyclic acetals, and also lactones and lactams.
Examples of epoxides are ethylene oxide, propylene oxide, butylene oxide and
styrene oxide.
Examples of cyclic ethers also include cyclic acetals, for example substituted
or unsubstituted
cyclic acetals having a ring size of 5 or 6 carbon atoms, which are derived
from aldehydes
having generally from 1 to 10 carbon atoms. This includes particularly
trioxane, 1,3-dioxane
and 1,3-dioxolane.
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Examples of cyclic ethers also include substituted or unsubstituted cyclic
monoethers having
a ring size of 4 or 5 atoms (oxetanes and furans), which generally have from 3
to 10 carbon
atoms, e.g., oxetane, 3,3-dimethyloxetane, tetrahydrofuran, 3-
methyltetrahydrofuran, 3,3-
dimethyltetrahydrofuran or 3,4-dimethyltetrahydrofuran.
Lactones suitable for the purposes of the present invention include for
example substituted or
unsubstituted lactones having a ring size of 4, 5, 6 or 7 atoms and having
generally from 3 to
carbon atoms, e.g., 13-propiolactone, y-butyrolactone, 8-valerolactone and c-
caprolactone.
10 Lactams suitable for the purposes of the present invention include for
example substituted or
unsubstituted lactams having a ring size of 4, 5, 6 or 7 atoms and having in
general from 3 to
10 carbon atoms, e.g., (3-propiolactam, y-butyrolactam, 6-valerolactam and e-
caprolactam.
The at least one monomer is specifically selected among acrylic acid, n-butyl
acrylate, benzyl
acrylate, 1,6-hexanediol diacrylate, 1,4-butanediol diacrylate, diethylene
glycol diacrylate,
triethylene glycol diacrylate, hydroxyethyl methacrylate (HEMA),
2-hydroxypropyl methacrylate (HPMA), 2-cyanoacrylates such as ethyl
cyanoacrylate (ECA), methacrylic acid, methyl methacrylate (MMA), n-butyl
methacrylate,
benzyl methacrylate, styrene, a-methylstyrene, 4-vinylpyridine, vinyl
chloride, methyl vinyl
ether, N-isopropylacrylamide (NIPAM), acrylamide, methacrylamide and mixtures
thereof.
In one embodiment of the present invention, the droplets of the first aerosol
stream further
comprise at least one nonpolymerizable additive. This additive has the
purpose, for example,
to modulate the physical, chemical or mechanical properties of the aerosol
droplets, for
example solution properties of monomers and polymers, surface tension, vapor
pressure,
droplet stability/viscosity, to thereby modify the properties of the
particles, for example the
particle structure, especially the shell morphology, or the chemical
properties of the shell, in a
specific manner.
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In principle, any additive can be used that, under the conditions of a
photopolymerization, is
not polymerizable and does not inhibit the polymerization of the monomers. It
is an essential
requirement of the optional additive that it does not absorb the entire
radiation made available
when the mixed aerosol stream is irradiated with electromagnetic radiation,
preferably UV
radiation. The additive referred to is preferably in particulate or dissolved
form. A person
skilled in the art will be aware of suitable additives in principle and will
select the additive
with reference to the property profile desired for the polymer shell. The
additive may be
liquid or solid.
Examples of additives are special-effect organics or inorganics, organic or
inorganic actives,
for example pharmaceutical, biological, insecticidal, pesticidal actives,
solvents, oils,
polymers and the like.
The amount in which the at least one additive is used for the purposes of the
present invention
is generally in the range from 0.1 to 40% by weight, preferably in the range
from 0.2 to 30%
by weight and more preferably in the range from 0.5 to 25% by weight, all
based on the
amount of the at least one monomer. The additive quantity may also be larger
in the case of
solvents.
When the solid additives referred to are added, the finely divided particles
of core-shell
structure which are obtained are hybridic in that they comprise at least one
polymer and/or
copolymer and at least one additive.
In one preferable embodiment, the optional additives are metals or oxides of
metals and/or
semimetals, for example selected among ZnO, Ti02, Fe oxides such as FeO, Fe203
and Fe304,
boric acid and borates, aluminum oxide, silicates, aluminosilicates, Si02 and
mixtures thereof.
Additives of this type are present in the monomers as a particulate solid. In
one more
preferable embodiment, the at least one additive, especially the oxide of the
metal and/or
semimetal, is in nanoparticulate form, i.e., has a diameter of 1 to 250 nm,
preferably 5 to
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100 nm and especially 10 to 50 nm. The nanoparticles may have any shape, for
example
sphere shaped, cube shaped, rod shaped.
In one embodiment of the present invention, at least one solvent is added to
the first aerosol
stream. Preferred solvents are solvents in which the at least one monomer is
soluble but the
polymer formed is insoluble.
Examples of solvents preferred according to the present invention are polar
organic solvents
such as alcohols, ketones, esters of carboxylic acids or mixtures thereof or
polar aprotic
organic solvents such as acetonitrile. Further possible solvents are aliphatic
and cycloaliphatic
hydrocarbons such as hexane, cyclohexane, methylcyclohexane, cyclic ethers
such as
tetrahydrofuran, dioxane and ionic liquids. Mixtures of the solvents mentioned
can also be
used.
Suitable alcohols include for example methanol, ethanol, propanols, such as n-
propanol,
isopropanol, butanols, such as n-butanol, isobutanol, tert-butanol, pentanols,
glycerol, glycol
and mixtures thereof. Suitable ketones include for example acetone, methyl
ethyl ketone and
mixtures thereof. Suitable esters of carboxylic acids include for example
ethyl acetate, methyl
acetate, butyl acetate and propyl acetate and mixtures thereof. It is
particularly preferable to
use ethanol or 1-propanol (n-propanol) as solvent.
When a solvent or solvent mixture is used, the amount of solvent is generally
in the range
from 10 to 80% by volume, preferably in the range from 30 to 70% by volume and
more
preferably in the range from 40 to 60% by volume, all based on the amount of
the at least one
monomer.
Suitable additives also include polymers and oils, for example polyethylene
glycol, ethylene
oxide-propylene oxide copolymers (E0-P0 copolymers), silicone oils and
mixtures thereof.
14
CA 02883037 2015-02-25
Step iv of the process according to the present invention subjects the
monomers in the first
aerosol stream to a polymerization triggered by exposure to electromagnetic
radiation.
Depending on the wavelength used for the electromagnetic radiation, the
optionally used
additives and the material in the second aerosol stream, at least one
photoinitiator will be
added to the monomers to initiate the polymers.
When at least one photoinitiator is used in the process of the present
invention, it will
typically be added to the monomer droplets of the first aerosol stream. Any
photoinitiator
known to a person skilled in the art as capable of effecting a free-radical or
ionic, i.e. cationic
or anionic, polymerization reaction of the at least one monomer used on
irradiation with
electromagnetic radiation is suitable for this in principle. Since the monomer
mixture is
irradiated with electromagnetic radiation for polymerization, it is preferable
for the purposes
of the present invention to use photoinitiators which on irradiation with
electromagnetic
radiation release a sufficiently large amount of (primary) free radicals or,
as the case may be,
cations or anions.
For the purposes of the present invention, electromagnetic radiation is to be
understood as
meaning electromagnetic radiation suitable for initiating a polymerization of
the at least one
monomer in the temperature range of the process according to the present
invention,
optionally using a photoinitiator. The electromagnetic radiation may comprise
x-rays or
gamma rays for example. Preferably, the electromagnetic radiation used for the
purposes of
the present invention comprises UV radiation or visible light, i.e.,
electromagnetic radiation
having a wavelength of 150 to 800 nm, preferably 180 to 500 nm, more
preferably 200 to
400 nm, and especially 250 to 350 nm. It is particularly preferable to use UV
radiation, i.e.,
light having a wavelength of not more than 400 nm, e.g., light having
wavelengths in the
range from 200 to 400 nm and especially in the range from 250 to 350 nm.
In one embodiment of the present invention, the droplets of the first aerosol
stream consist
essentially exclusively of the at least one monomer and at least one
photoinitiator, i.e., the
concentration of the at least one monomer and of the at least one
photoinitiator is in the range
CA 02883037 2015-02-25
from 80 to 100% by weight, preferably in the range from 90 to 100% by weight
and
especially in the range from 95 to 100% by weight, based on the total mass of
droplets.
Examples of preferred photoinitiators for a free-radical polymerization are 2-
methyl-
1[4-(methylthio)pheny1]-2-morpholinopropan-l-one (obtainable for example under
the brand
name Irgacure 907 from BASF SE), 2,2`-azobisisobutyronitrile (AIBN) and
further,
asymmetrical azo derivatives, benzoin, benzoin alkyl ether, benzoin
derivatives,
acetophenones, benzil ketals, -hydroxyalkylphenones, LI -aminoalkylphenones, 0-
acyl- LI -
oximinoketones, (bi)acylphosphine oxides, thioxanthone (derivatives) and
mixtures thereof
Examples of preferred photoinitiators for a cationic photopolymerization are
selected among
substituted diaryliodonium salts, substituted triarylphosphonium salts and
mixtures thereof.
Examples of preferred photoinitiators for an anionic photopolymerization are
selected among
transition metal complexes, N-alkoxypyridinium salts, N-phenylacylpyridinium
salts and
mixtures thereof
A so-called living anionic polymerization in the purely polymeric batch can
also be carried
out, optionally comprising a secondary functionalization using terminating
reagent, for
example by jetting a gaseous or vaporizable chemical compound into the aerosol
space,
preferably into the unilluminated residence zone.
In the embodiment utilizing at least one photoinitiator, the amount of
photoinitiator in the
droplets of the first aerosol stream is for example in the range from 0.1 to
10% by weight,
preferably in the range from 0.5 to 8% by weight and more preferably in the
range from 0.8 to
5% by weight, all based on the amount of the at least one monomer present.
In one preferable embodiment of the present invention, no photoinitiator is
added to the first
aerosol stream, i.e., the concentration of photoinitiator in the first aerosol
stream is less than
0.01% by weight, based on the total mass of droplets. This embodiment comes
into
16
CA 02883037 2015-02-25
consideration for example when the solid particles of the second aerosol
stream, for example
ZnO and/or Ti02, are capable of initiating the photopolymerization in step iv.
Alternatively,
the photopolymerization in this embodiment can also be triggered using high-
energy
radiation, for example x-rays or gamma rays.
Any desired solid particles can generally be used in the second aerosol stream
in the context
of the present invention. Solid organic, organometallic and inorganic
compounds or metals,
semimetals and nonmetals may be concerned here. Preferably, the solid
particles are selected
among oxides, sulfides, carbides, nitrides, carbonates, phosphates and halides
of metals or of
semimetals, metal carbonyls, elemental metals, elemental semimetals and metal
alloys.
Examples are elemental metals such as Cu, Ag, Au, Pd, Pt and oxides of
semimetal or metal,
sulfides, nitrides and carbides, such as Si02, SiC, BN, silicates,
aluminosilicates, ZnO, ZnS,
Ti02, A1203, metal halides such as NaC1, tungsten oxides such as W02, W03 and
W203.
The particles used in the second aerosol stream are naturally finely divided
particles which
preferably have a number-average particle diameter in the range from 20 nm to
30 pm,
frequently in the range from 25 nm to 10 p.m, especially in the range from 30
nm to 1 1.tm and
specifically in the range from 40 to 500 nm. The particle size distribution is
preferably
monomodal, i.e., the distribution curve has only one maximum. Distribution
spread is
preferably not very wide. More particularly, finely divided particles having a
narrow spread of
distribution are used, especially those where the distribution spread Q has
values in the range
from 1.0 to 1.2:
Q = (D90 - Dm) / Dso
D50 is the median particle diameter,
D90 is the particle diameter than which 90% of the particles are smaller, and
D10 is the particle diameter than which 10% of the particles are smaller.
17
CA 02883037 2015-02-25
The particle diameters indicated here and hereinbelow relate to the particle
masses determined
using a differential mobility analyzer and the particle diameters computed
therefrom assuming
spherical particles.
The first and second aerosol stream may generally be provided by any process
known to a
person skilled in the art, and/or by using suitable carrier gases and devices
which are common
general knowledge among those skilled in the art. The aerosol streams are more
preferably
provided in a nebulizer or atomizer using a one- or multi-material nozzle or
using an
electrospray or using an ultrasonic nebulizer. When the aerosol streams are
produced using
nozzles, the nozzles for producing the first and second aerosol stream
generally each have an
inlet pressure of 1 to 10 bar, especially 1 to 3 bar.
A suitable choice of atomizer and also of its operating conditions, or
classification using a
differential mobility analyzer (DMA) for example, further enables achieving
particularly
narrowly distributed droplet or particle size distributions.
The carrier gas stream used to produce the first and second aerosol stream may
be an inert
gas stream, for example selected among nitrogen (N2), carbon dioxide (CO2),
argon (Ar),
helium (He) and mixtures thereof, or air or mixtures with air such as lean air
for example.
When the polymerization is photoinitiated and conducted free-radically, the
use of an inert
gas stream is preferable. When the polymerization is initiated and conducted
cationically, the
use of an air or inert gas stream is preferable. The carrier gas stream is
preferably an inert gas
stream. More particularly, N2 (nitrogen) is used to form the inert gas stream.
This nitrogen can
come from any source known to a person skilled in the art, for example from
commercially
available stock reservoir bottles, from the distillation of air, etc. The
other inert gases
mentioned can likewise come from sources known to a person skilled in the art.
When air is
used, it is preferable to use ambient air or compressed air.
The pressure in the carrier gas stream for the purposes of the present
invention is preferably
equal to atmospheric pressure or slightly elevated atmospheric pressure. For
the purposes of
18
CA 02883037 2015-02-25
the present invention, "slightly elevated atmospheric pressure" is to be
understood as meaning
a pressure which is from 1 to 500 mbar above atmospheric pressure for example.
This
preferably slightly elevated pressure has the particular purpose of assisting
the carrier gas
stream in overcoming the resistance of downstream parts of the apparatus, as
of a filter or of a
separation liquid for example.
The first aerosol stream comprises droplets in a carrier gas stream which
comprise the at least
one monomer. The process of the present invention is generally conducted such
that droplet
density in the carrier gas stream is in the range from 104 to 1010 droplets
per cm3, preferably in
the range from 106 to 108 droplets per cm3 and most preferably in the range
from 107 to 108
droplets per cm3. Droplet density can be determined using a scanning mobility
particle sizer
(SMPS) or a condensation particle counter for example.
The amount introduced into the carrier gas stream of at least one monomer and
optionally at
least one photoinitiator and optionally at least one nonpolymerizable additive
is determined
for the purposes of the present invention such that an appropriate number of
particles per
volume is obtained. The amount of at least one monomer can be used to compute
the size of
droplets of liquid formed in the aerosol and hence the size of the finely
divided particles
obtained after the polymerization.
The number-average droplet diameter is generally chosen such that it is in the
range from 20
nm to 30 1AM, frequently in the range from 25 to 5000 nm, especially in the
range from 30 nm
to 1000 tun and specifically in the range from 30 to 500 nm. Droplet diameter
is typically set
by the choice of operating conditions for the atomizer, for example by the
inlet pressure for
the atomizer, the ratio of gas flow to liquid flow, etc. In the electrospray
process, for example,
voltage can be varied, while in the case of an ultrasonic nebulizer the energy
input can be
varied. In addition, a certain size fraction can be selected via a DMA.
To provide the second aerosol stream, a suspension of solid particles is
typically converted
into an aerosol stream using a gas. The suspension used for providing the
second aerosol
19
CA 02883037 2015-02-25
stream generally has a solids content of 0.01 to 10 mg/mL and preferably of
0.1 to 3 mg/mL.
A multiplicity of liquids can be used as liquid suspension medium, preferably
liquids which
have an atmospheric pressure boiling point in the range from 30 to 120 C and
especially in
the range from 40 to 100 C. Preferred liquids are polar solvents such as
water, alkanols such
as methanol, ethanol, n-propanol, isopropanol or else hydrocarbons. Mixtures
of various
solvents can also be used. Water is used in particular.
The water-laden aerosol obtained for the second aerosol stream on using water
as solvent
passes, after it has been produced, through a suitable dryer, for example a
diffusion dryer, to
remove the solvent, generally water.
In one embodiment, the solid particles can also be atomized using other,
mechanical devices
such as a brush feeder for example.
It is also possible to produce the solid particles of the second aerosol
stream from the liquid
droplets of a previous aerosol stream. A solution of the material which is
later to form the
solid particles of the second aerosol stream, e.g., sodium chloride, in a
solvent, e.g., water, is
generally prepared for this. This mixture is for example atomized in a two-
material nozzle by
means of a carrier gas stream such as nitrogen at a nozzle inlet pressure of 1
bar. The aerosol
obtained is passed through a dryer, for example diffusion dryer, to remove the
solvent, e.g.,
water, substantially or completely. In this way, the liquid droplets of the
previous aerosol
stream are converted into an aerosol stream of solid particles, e.g.,
nanoscale sodium chloride
particles. This aerosol stream of solid particles is preferably used without
intermediate
isolation as the second aerosol stream in the process of the present
invention.
The second aerosol stream provided according to the present invention
comprises solid
particles in a carrier gas stream. The process of the present invention is
generally carried out
such that particle density in the carrier gas stream is in the range from 104
to 1010 particles per
cm3, preferably in the range from 104 to 108 particles per cm3 and most
preferably in the range
CA 02883037 2015-02-25
from 104 to 106 particles per cm3. Particle density can be determined using a
scanning
mobility particle sizer (SMPS) or a condensation particle counter for example.
According to the present invention, the droplets of the first aerosol stream
and the particles of
the second aerosol stream are given opposite charges before mixing. The
droplets of the first
aerosol stream may be given not only a negative charge but also a positive
charge. The solid
particles of the second aerosol stream are given whichever is the opposite
charge. In one
specific embodiment of the present invention, the droplets of the first
aerosol stream are given
a negative charge and the particles of the second aerosol stream are given a
positive charge.
To provide the first aerosol stream comprising charged droplets comprising at
least one
monomer, an aerosol stream of essentially uncharged droplets comprising at
least one
monomer is produced and passed through an electric charger to charge up the
droplets, for
example a corona charger.
The second aerosol stream is generally provided in a corresponding manner by
producing an
aerosol stream of essentially uncharged particles and passing it through an
electric charger,
for example a corona charger, to charge up the droplets. corona chargers are
based on the
principle of gas discharge due to applying a high voltage. When the voltage is
sufficiently
high, a gas discharge occurs and a strong electrical field is formed.
Depending on the size of
particles used, either field charging or diffusion charging can take place.
The mechanism of
field charging is dominant for particles 1 p.m or more in diameter. The ions
produced due to
the gas discharge move along the field lines. When these field lines end on
the particle
surface, there is an impact of ions, resulting in a particle charge. In the
case of smaller particle
diameters (< 1 pm), the ions collide with the particles as a result of
stochastic movements
(diffusion charging). This process continues even after the charger has been
left behind.
Processing conditions and settings in the charger can be chosen to effect
unipolar charging of
the particles and droplets in a specific manner and to adjust charge density
in the aerosol
stream.
21
I
CA 02883037 2015-02-25
The aerosol of the first aerosol stream is given a unipolar, preferably
negative, charge by
using the charger.
The aerosol of the second aerosol stream is given a charge which is likewise
unipolar, and
opposite to that of the first aerosol stream, i.e. preferably positive, by
using a charger. Useful
chargers for the second aerosol stream, in addition to the corona charger
already mentioned,
also include UV chargers or chargers with radioactive sources (bipolar
chargers). UV chargers
offer a further way to generate an aerosol having a unipolar charge. When the
high-energy
photons collide with aerosol particles, electrons are emitted and positively
charged particles
stay behind. This photoeffect is dependent on the material to be charged and
also on the
wavelength of radiation. The unipolar charging of the particles of the second
aerosol stream
can also be accomplished by using a radioactive source such as Kr85 for
example. The
radioactive decay produces ionizing radiation which generates not only
negative but also
positive ions. This ion mixture produces a Boltzmann charge distribution
centered on 0
charges. Increasing diameter of the aerosol particles increases the
probability of multiple
charging. Corona chargers are preferred for the unipolar charging of the
aerosol of the second
aerosol stream.
Chargers are preferably constructed with a spray electrode on the inside, to
which high
voltage is applied. The voltage applied to the spray electrode of the charger
is preferably 2 to
6 kV and especially 2 to 4 kV for the first aerosol stream. The voltage
applied to the spray
electrode of the charger is preferably 2 to 6 kV and especially 3 to 5 kV for
the second aerosol
stream.
The mixing ratio of first to second aerosol stream is generally chosen such
that the ratio of the
volume flow of the first aerosol stream to the volume flow of the second
aerosol stream is in
the range from 8:1 to 1:8 and especially in the range from 3:1 to 1:3.
In the process of the present invention, the first aerosol stream comprising
droplets
comprising at least one monomer, optionally comprising at least one
photoinitiator, optionally
22
CA 02883037 2015-02-25
comprising at least one additive, is mixed with the second aerosol stream
comprising solid
particles to obtain a mixed aerosol stream. Mixing can in principle be
effected using measures
of the kind known for mixing of gases or aerosol streams, for example by
passing the two
aerosol streams into a mixing zone or bringing the two aerosol streams
together in a suitable
manner. The mixing zone may be designed as a mixing chamber for example. In
this case, the
two aerosol streams will be passed into the mixing chamber and the mixed
aerosol stream is
removed from the mixing chamber. The mixing zone can also be designed as a
tubular zone,
i.e., as a mixing sector. In this case, the two aerosol streams will be
brought together in the
tubular zone in a suitable manner, for example by feeding them conjointly into
a zone of
tubular design, for example via a Y- or T-piece. Mixing within the mixing
zone/sector may
also be accelerated using internals known to a person skilled in the art such
as static mixers
for example.
The mixing zone/sector in a preferable embodiment is extended to an
unilluminated residence
zone. This residence zone promotes the coming together of the differing
charged particles to
form finely divided core-shell particles which in addition to a solid core
further include a
liquid shell comprising the monomers. Thereafter, the polymerization of the
monomers is then
initiated in the polymerization zone, and the shell of the finely divided core-
shell particles
solidifies. The average residence time of the mixed aerosol stream in the
unilluminated
residence zone is preferably in the range from 1 to 500 sec and especially in
the range from 10
to 100 sec.
The mixed aerosol stream thus obtained is subsequently irradiated with
electromagnetic
radiation, for example with light, preferably UV radiation, or with high-
energy radiation, so
the monomers present polymerize. The irradiating is naturally effected in a
reaction zone,
hereinafter also called photoreactor, that is downstream of the mixing zone.
In a further preferred embodiment of the present invention, the mixed aerosol
stream passes
for photopolymerization through a flow photoreactor. The average residence
time of the
23
CA 02883037 2015-02-25
mixed aerosol stream in the flowthrough photoreactor is in the range from 1 to
300 sec and
especially in the range from 5 to 60 sec.
Irradiating the carrier gas stream with electromagnetic radiation in the
manner of the present
invention can generally be effected in any apparatus known to a person skilled
in the art. UV
radiation is preferably used for the purposes of the present invention. It can
be produced by
any apparatus known to a person skilled in the art, for example LEDs, excimer
radiators, for
example with xenon chloride (XeCl, 308 nm), xenon fluoride (XeF, 351 nm),
krypton fluoride
(KrF, 249 nm), krypton chloride (KrCI, 222 nm), argon fluoride (ArF, 193 nm)
or Xe2 (172
nm) as radiation-active medium, for example at 10 mW/cm2 on the radiator
surface, or with a
UV fluorescence tube, for example at 8 mW/cm2 on the radiator surface. The use
of an
excimer radiator is advantageous, since it is dimmable by pulsed operation,
for example down
to 10 to 100%. This makes optimizing the polymerization process a relatively
simple matter.
In a preferred embodiment of the process according to the present invention,
the inside wall of
the photoreactor is flushed with air, lean air or an inert gas, for example
with N2, Ar, He, CO2
or mixtures thereof. This has the purpose for example of minimizing wall
losses due to
polymer film formation.
In a further embodiment of the process according to the present invention, a
reactive gas can
additionally be injected for secondary functionalization of the finely divided
particles formed.
The process of the present invention, especially steps i to iv are generally
carried out at a
temperature in the range from 0 to 100 C, especially in the range from 10 to
50 C and
specifically in the range from 20 to 30 C.
Therefore, after emerging from the photoreactors which are preferably used for
the purposes
of the present invention, the polymerization within the finely divided
particles will have
substantially concluded to obtain corresponding finely divided particles of
core-shell structure
which have a solid surface and therefore do not undergo any further change in
the course of
24
CA 02883037 2015-02-25
the subsequent process steps, for example removing the finely divided
particles formed. The
finely divided particles obtained according to the present invention have a
core-shell structure,
i.e., the core of the finely divided core-shell particles consists of the
solid particles of the
second aerosol stream and the shell consists of the polymerized monomers and
also optionally
of the at least one nonpolymerizable additive of the first aerosol stream. The
finely divided
particles obtained according to the present invention have a particularly
homogeneous core-
shell structure. A further advantage is that the size the droplets and of the
size of the solid
particles largely predefines the size of the core-shell particles obtained.
The droplet size set
via the atomizer can thus be used to directly set the resulting particle size
and the shell
thickness.
In a further process step, the finely divided particles formed can be removed
from the carrier
gas. Removal can in principle be effected by any process known to a person
skilled in the art.
In a preferred embodiment, the finely divided particles formed are removed by
collection on a
filter and in a further preferred embodiment by introduction into a liquid
medium. Collection
in a liquid can be effected using a wash bottle or a wet electrofilter for
example.
The liquid medium which is optionally used for collecting can be selected
among water,
ethanol, organic solvents, for example apolar solvents of any kind, for
example alkanes,
cycloalkanes and mixtures thereof. Introducing the finely divided particles
produced into the
liquid medium gives a suspension of the finely divided particles in the liquid
medium. This
suspension can be further processed to recover the particles, for example by
separating the
finely divided particles from the suspension, or this suspension constitutes
the process product
desired according to the present invention and can be introduced directly into
the
corresponding use. To ensure long-term survival of the resulting particle
sizes, further
additives can be added to the core-shell particles to stabilize the particles
against
agglomeration and thereby avoid agglomeration of the core-shell particles
obtained.
CA 02883037 2015-02-25
The finely divided particles can also be collected with a filter. Suitable
filters are known per
se to a person skilled in the art, examples being polyamide filters,
polycarbonate filters, PTFE
filters, with pore sizes of 50 nm for example, electrofilters.
The process of the present invention provides finely divided particles of core-
shell structure
where the shell comprises at least one polymer and/or copolymer formed from
the monomers
of the first aerosol stream. For the purposes of the present invention, the
term "finely divided
particles" is to be understood as meaning particles that have a number-average
particle
diameter in the range from 25 nm to 30 Jim, frequently in the range from 25 nm
to 101.tm,
especially in the range from 30 nm to 1 p.m and specifically in the range from
40 to 500 nm.
The process of the present invention naturally provides compositions
comprising a
multiplicity of these finely divided particles. Median particle size and the
particle size
distribution of the finely divided particles in these compositions are
naturally determined by
the particle size distribution of the particles of the second aerosol stream.
The particle size
distribution is preferably monomodal, i.e., the distribution curve has only
one maximum.
Distribution spread is preferably not very wide. The process of the present
invention is
capable of achieving distribution spreads Q having values in the range from
1.0 to 1.2.
The finely divided particles obtainable according to the present invention are
novel and
likewise form part of the subject matter of the present invention.
The present invention also provides compositions of finely divided particles,
for example
dispersions of finely divided particles and powders of finely divided
particles, wherein the
finely divided particles are selected among the finely divided particles of
the present
invention.
The core of the finely divided particles of core-shell structure is generally
formed of a solid
organic, inorganic or organometallic material. The core of the core-shell
particles generally
26
CA 02883037 2015-02-25
comprises on average from 1 to 99.9% by volume, especially from 10 to 95% by
volume and
specifically from 50 to 90% by volume based on the total volume of the
particles.
The average molecular weight of the uncrosslinked polymer sheath of core-shell
particles can
be determined using GPC. The number-average molecular weight of the polymer
sheaths is
generally in the range from 1000 to 1 000 000 g/mol, frequently 5000 to 100
000 g/mol,
especially 10 000 to 80 000 g/mol and specifically 10 000 to 60 000 g/mol.
The process of the present invention can be designed as a batch process or as
a continuous
process. The process of the present invention is preferably conducted as a
continuous
operation.
Figure description:
Figures 1 and 2 show transmission electron micrographs of a finely divided
particle of core-
shell structure obtained in Example 1.
Figure 3 shows a transmission electron micrograph of a finely divided particle
of core-shell
structure obtained in Example 2.
Figure 4 shows a transmission electron micrograph of a finely divided particle
of core-shell
structure obtained in Example 3.
Figure 5 shows a transmission electron micrograph of a finely divided particle
of core-shell
structure obtained in Example 4.
Figure 6 shows a transmission electron micrograph of finely divided particles
of core-shell
structure obtained in Example 5.
27
CA 02883037 2015-02-25
Examples:
Analytical methods:
Transmission electron microscopy (TEM) can be used to visualize the cores and
shells of the
core-shell particles. Fourier transform infrared spectroscopy (FTIR) is used
as spectroscopic
method to show that the double bonds of the monomer molecules are absent in
the polymer
structures, and/or that the liquid monomer layer has become solid polymer. Gel
permeation
chromatography (GPC) can be used to determine the average molecular weight of
the polymer
sheath.
General experimental procedure:
To produce the first aerosol stream, the solution of at least one monomer,
optionally at least
one photoinitiator, optionally at least one additive and optionally at least
one crosslinker is fed
by means of the carrier gas stream into an ATM 220 atomizer with two-material
nozzle from
Topas. After emerging from the atomizer, the aerosol is electrically charged
up in a corona
charger.
To produce the second aerosol stream, the suspension of solid particles in,
for example, water
is fed by means of the carrier gas stream into an ATM 220 atomizer with two-
material nozzle
from Topas. The aerosol subsequently flows through a DDU 570/I-I diffusion
dryer from
Topas to minimize the water content of the aerosol. On emerging from the
atomizer, the
aerosol is electrically charged up in a corona charger with the opposite
charge to the first
aerosol stream.
To produce the second aerosol stream of solid sodium chloride particles in
Examples 4 and 5,
the second aerosol stream is provided according to the following method: A
solution of
sodium chloride in water having a solids content of 3.5 mg of sodium chloride
per 1 mL of
water is prepared. This mixture is atomized in a two-material nozzle at a
nozzle inlet pressure
28
CA 02883037 2015-02-25
of 1 bar by means of the carrier gas stream. The aerosol produced, which
consists of water
droplets comprising sodium chloride, is passed through a diffusion dryer. On
emerging from
the diffusion dryer, the second aerosol stream of solid, nanoscale sodium
chloride particles is
obtained and electrically charged up in a corona charger with the opposite
charge to the first
aerosol stream.
The first and second aerosol streams are brought together and flow through a
darkened
residence zone. The mixed aerosol stream then flows through one of the two
self-built
photoreactors, photoreactor 1 or 2 (photoreactor 1 has a UV source comprising
an XeC1
excimer radiator with a photon power output of 10 mW/cm2 on the radiator
surface. The UV
radiator in this photoreactor is centered, so irradiation takes place toward
the outside.
Photoreactor 2 consists of 3 identical UV radiators, each equipped with a UV
fluorescence
tube and a photon power output of 8 mW/cm2 on the radiator surface. In this
photoreactor, the
UV radiators are outside the reaction volume, so irradiation takes place
toward the inside).
Nitrogen (N2) was used as carrier gas in all examples.
List of chemicals used:
- methyl methacrylate
n-butyl acrylate
1,6-hexanediol diacrylate
-
Irgacure 907 photoinitiator (from BASF SE) (2-methyl-1[4-(methylthio)pheny1]-
2-
morpholinopropan-l-one)
- spherical, nanoscale silicon dioxide, particle diameter 250 nm (from
Microparticles)
substantially spherical, nanoscale gold, particle diameter 100 nm (from
Postnova)
nanoscale zinc oxide: 40% by weight of zinc oxide nanoparticles in ethanol,
particle
diameter 30 nm (from Sigma Aldrich)
sodium chloride
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CA 02883037 2015-02-25
Example 1:
First aerosol stream:
Monomer: methyl methacrylate
Photoinitiator: Irgacure 907, 1% by weight in methyl methacrylate
Crosslinker: 1,6-hexanediol diacrylate, 10% by volume based on the
amount of methyl
methacrylate
Nozzle inlet pressure: 1 bar
Charging voltage: 2 kV
Polarity of droplets: negative
Concentration of monomer droplets in the aerosol: 107 to 108 droplets/cm3
Mean droplet diameter: 131.4 nm, standard deviation 0.5711m
Elementary charges per droplet: 10 to 60, depending on the diameter
Second aerosol stream:
Solid material: spherical, nanoscale silicon dioxide
Concentration: 1 mg of Si02 per 1 mL of H20
Nozzle inlet pressure: 2 bar
Charging voltage: 4 kV
Polarity of particles: positive
Concentration of particles in the aerosol: 105 particles/cm3
Mean particle diameter: 250 nm, standard deviation 0.1 p.m
Elementary charges per particle: 40
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CA 02883037 2015-02-25
Mixed aerosol stream:
Residence time in unilluminated residence zone: 10 sec
Irradiation time: 3 min
Photoreactor: photoreactor 1
Example 2:
First aerosol stream:
Monomer: methyl methacrylate
Photoinitiator: Irgacure 907, 1% by weight in methyl methacrylate
Crosslinker: 1,6-hexanediol diacrylate, 10% by volume, based on the
amount of methyl
methacrylate
Nozzle inlet pressure: 1 bar
Charging voltage: 2 kV
Polarity of droplets: negative
Concentration of monomer droplets in the aerosol: 107 to 108 droplets/cm3
Mean droplet diameter: 131.4 nm, standard deviation 0.571AM
Elementary charges per droplet: 10 to 60, depending on the diameter
Second aerosol stream:
Solid material: approximately spherical, nanoscale gold
Concentration: 0.6 mg of Au per 1 mL of H20
Nozzle inlet pressure: 2 bar
Charging voltage: 4 kV
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CA 02883037 2015-02-25
Polarity of particles: positive
Concentration of particles in the aerosol: 105 particles/cm3
Mean particle diameter: 100 nm
Elementary charges per particle: 20
Mixed aerosol stream:
Residence time in unilluminated residence zone: 10 sec
Irradiation time: 3 min
Photoreactor: photoreactor 2
Example 3:
First aerosol stream:
Monomer: methyl methacrylate
Photoinitiator: Irgacure 907, 1% by weight, in methyl methacrylate
Crosslinker: 1,6-hexanediol diacrylate, 10% by volume, based on the
amount of methyl
methacrylate
Ethanol: 0.2 mL of suspension of zinc oxide nanoparticles in ethanol
per 15 ml of
methyl methacrylate, this suspension is added to the monomer solution.
Nozzle inlet pressure: 1 bar
Charging voltage: 2 kV
Polarity of droplets: negative
Concentration of monomer droplets in the aerosol: 107 to 108 droplets/cm3
Mean droplet diameter: 131.4 nm, standard deviation 0.57 um
Elementary charges per droplet: 10 to 60, depending on the diameter
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CA 02883037 2015-02-25
Second aerosol stream:
Solid material: spherical, nanoscale silicon dioxide
Concentration: 1 mg of Si02 per 1 mL of H20
Nozzle inlet pressure: 2 bar
Charging voltage: 4 kV
Polarity of particles: positive
Concentration of particles in the aerosol: 105 particles/cm3
Mean particle diameter: 250 nm, standard deviation 0.1 [Am
Elementary charges per particle: 40
Mixed aerosol stream:
Residence time in unilluminated residence zone: 10 sec
Irradiation time: 3 min
Photoreactor: photoreactor 2
Example 4:
First aerosol stream:
Monomer: methyl methacrylate
Photoinitiator: Irgacure0 907, 1% by weight in methyl methacrylate
Crosslinker: 1,6-hexanediol diacrylate, 10% by volume based on the
amount of methyl
methacrylate
Nozzle inlet pressure: 1 bar
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CA 02883037 2015-02-25
Charging voltage: 3.5 kV
Polarity of droplets: negative
Concentration of monomer droplets in the aerosol: about 107 droplets/cm3
Mean droplet diameter: about 130 nm
Elementary charges per droplet: about 10 to 60, depending on the diameter
Second aerosol stream:
Solid material: nanoscale sodium chloride
Nozzle inlet pressure: 2 bar
Charging voltage: 4 kV
Polarity of particles: positive
Concentration of particles in the aerosol: about 107 particles/cm3
Mean particle diameter: about 65 nm
Elementary charges per particle: about 10 to 60, depending on the diameter
Mixed aerosol stream:
Residence time in unilluminated residence zone: 60 sec
Irradiation time: 3 min
Photoreactor: photoreactor 2
Example 5:
First aerosol stream:
Monomer: 1,6-hexanediol diacrylate
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CA 02883037 2015-02-25
Photoinitiator: Irgacure0 907, 1% by weight in 1,6-hexanediol diacrylate
Crosslinker: -
Nozzle inlet pressure: 1 bar
Charging voltage: 3.5 kV
Polarity of droplets: negative
Concentration of monomer droplets in the aerosol: about 107 droplets/cm3
Mean droplet diameter: about 130 nm
Elementary charges per droplet: about 10 to 60, depending on the diameter
Second aerosol stream:
Solid material: nanoscale sodium chloride
Nozzle inlet pressure: 2 bar
Charging voltage: 4 kV
Polarity of particles: positive
Concentration of particles in the aerosol: about 107 particles/cm3
Mean particle diameter: about 65 nm
Elementary charges per particle: about 10 to 60, depending on the diameter
Mixed aerosol stream:
Residence time in unilluminated residence zone: 60 sec
Irradiation time: 3 min
Photoreactor: photoreactor 2
CA 02883037 2015-02-25
Example 6:
Finely divided particles of core-shell structure were produced similarly to
Example 1. Butyl
acrylate was used as monomer in the first aerosol stream. Photoinitiator was
used but no
crosslinker. The solid material in the second aerosol stream was spherical,
nanoscale silicon
dioxide.
The finely divided particles obtained had cores of spherical, nanoscale
silicon dioxide and
shells of poly(n-butyl acrylate).
Since no crosslinker was added, the shells of the finely divided particles of
core-shell
structure could not be seen in the transmission electron micrographs.
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