Process for preparing a stable dispersion in an aqueous medium of particles of polymer

A process for preparing a stable dispersion in an aqueous medium of particles of polymer, said process comprising the steps of: PA0 (a) reacting at least one radically polymerizable monomer in an organic liquid in the presence of a dispersion stabilizer for the particles to form particles of polymer insoluble in said organic liquid and water, said stabilizer being a resin having in each of its molecules on the average at least 0.3 unit of a polymerizable double bond and a functional group that can be neutralized with an acid or a base, said resin being capable of being emulsifiably dispersed or dissolved in an aqueous medium by neutralization; PA0 (b) neutralizing with acids or bases the functional group of the resin as a dispersion stabilizer; and PA0 (c) replacing the organic liquid of the resulting dispersion of polymer particles with an aqueous medium.

This invention relates to a process for preparing a stable dispersion in an 
aqueous medium of particles of polymer. 
The aqueous dispersion of particles of polymer is usually prepared by such 
methods as the emulsion polymerization method in which an ionic or 
non-ionic surfactant is used or the self-emulsifying dispersion method 
which involves neutralizing with a low molecular weight acid or base a 
carboxyl or basic group-containing polymer that is formed in a liquid 
medium consisting predominantly of a water-miscible organic solvent and 
thereafter dispersing the neutralized product in an aqueous medium. 
The emulsion polymerization method does suffer from certain limitations. 
One of these is the difficulty of choosing and using water-soluble 
monomers. Another drawbacks associated with aqueous emulsion 
polymerization is the fact that the presence of the surfactant and 
decomposed slices of an ionic polymerization initiator may deteriorate the 
film performance which can be attained in coating compositions based upon 
the resulting dispersion; for example, it is often difficult to obtain 
thermosetting films of high water resistance and weather-ability from such 
compositions. 
On the other hand, the self-emulsifying dispersion method has the defect 
that the stability of the aqueous dispersion obtained is greatly 
influenced by the class and amount of the water-miscible solvent used and 
the polarity (degree of hydrophilicity) of polymer dispersed. 
As a method of improving on these defects, there is disclosed in U.S. Pat. 
No. 4,209,435 (Japanese Laid-Open Patent Publication No. 66,949/1979) a 
method which comprises preparing in a nonaqueous liquid predominantly of 
an aliphatic hydrocarbon and in the presence of a steric stabilizer, a 
dispersion of polymer particles insoluble in said nonaqueous liquid 
(so-called nonaqueous polymer dispersion), and thereafter causing the 
migration of the polymer particles from the nonaqueous liquid to an 
aqueous medium by the use of a high molecular protective colloid comprised 
of a neutralized water-soluble polymer. 
The stabilization of the polymer particles by this method are achieved by 
the formation of a steric barrier (steric repelling layer) of the high 
molecular protective colloid around the polymer particles. In addition, 
since the high molecular protective colloid is electrically charged to a 
certain degree, the stability of the polymer particles is further enhanced 
by its electrical repulsive force. 
The degree to which the water-soluble polymer used as the high molecular 
protective colloid can adhere to the steric stabilizer that is bound to 
the surface of the polymer particles is however greatly influenced by the 
solubility of said water-soluble polymer in the aqueous medium or its 
affinity for the polymer particles and steric stabilizer. Hence, for 
obtaining a dispersion that is stable in practical applications, there are 
imposed restrictions as to how the steric stabilizer, high molecular 
protective colloid and polymer particles are combined. Difficulty is thus 
experienced in planning and preparing the dispersion. There is a further 
defect in that in the case where the dispersed particles in the nonaqueous 
liquid are not crosslinked to a high degree the dispersed particles are 
swelled or partially dissolved by the polar monomer that is used when the 
polymer to be used as the high molecular protective colloid is being 
synthesized in the presence of the dispersed particles, with the 
consequence that the viscosity of the whole dispersion system is 
increased. There is thus imposed a restriction on the use of the polar 
monomer. Further, the rate of feed of the monomers is also responsible for 
increasing the viscosity. This also makes it difficult to control the 
reaction system. 
Such being the case, extensive researches were carried out by the present 
inventors with the view of developing a process for preparing a stable 
dispersion in an aqueous medium of particles of polymer free of the 
aforementioned defects, and the present inventors finally succeeded in 
perfecting the present invention. 
There is thus provided in accordance with the present invention a process 
for preparing a stable dispersion in an aqueous medium of particles of 
polymer, which comprises the steps of: 
(a) reacting at least one radically polymerizable monomer in an organic 
liquid in the presence of a dispersion stabilizer for the particles to 
form particles of polymer insoluble in said organic liquid and water, said 
stabilizer being a resin having in each of its molecules on the average at 
least 0.3 unit of a polymerizable double bond and a functional group that 
can be neutralized with an acid or a base (hereinafter referred to as 
neutralizable group), said resin being capable of being emulsifiably 
dispersed or dissolved in an aqueous medium by neutralization; 
(b) neutralizing with an acid or a base the functional group of the resin 
has as a dispersion stabilizer; and 
(c) replacing the organic liquid of the resulting dispersion of polymer 
particles with an aqueous medium. 
The resin used as dispersion stabilizer in step (a) of this invention 
(hereinafter referred to as dispersion stabilizer resin) is a resin having 
in its molecular chain on the average per molecule at least 0.3, 
preferably 0.3 to 3, and more preferably 0.7 to 1 polymerizable double 
bond, as well as a neutralizable group. Examples include those based on 
the acrylic resins, polyester resins and alkyd resins. 
As neutralizable groups in the aforesaid resins, those that can be 
neutralized with bases include, for example the carboxyl, phosphoric acid 
and sulfonic acid groups. On the other hand, an example of the group that 
can be neutralized with an acid is the amino group. These neutralizable 
groups can be present in the molecular chain in an amount that is 
sufficient for emulsifiably dispersing or dissolving the dispersion 
stabilizer resin in an aqueous medium by its neutralization with the 
hereinafter mentioned acids or bases. More specifically, while the amount 
that can be present will depend upon the resin that is used as the base, 
usually the amount ranges from 20 to 200, and preferably from 35 to 100, 
in terms of the acid or amine value. 
Further, in view of the fact that the dispersion stabilizer resin must be 
dissolved in an organic liquid of low polarity, it preferably is of low 
polarity. 
Typical examples of the dispersion stabilizer resin that can be 
advantageously used in step (a) in accordance with this invention will now 
be more specifically described. 
(A) Acrylic Resins 
The acrylic resins can be synthesized in the following manner. For example, 
2 to 30% by weight of an unsaturated monomer containing at least one 
carboxyl group is used as the requisite polymerization component, and this 
is copolymerized with at least one other radically polymerizable monomer 
to give an acrylic copolymer (base resin). A part of the carboxyl groups 
of the thus obtained resin is then reacted with the glycidyl groups of a 
glycidyl group-containing unsaturated monomer to synthesize the intended 
acrylic resin. There is thus obtained an acrylic resin having a carboxyl 
group that can be neutralized. This resin is effectively used as an 
anionic dispersion stabilizer. 
Again, an acrylic resin can be obtained by using as the requisite 
polymerization components 2 to 30% by weight of an unsaturated monomer 
containing at least one tertiary amino group and 2 to 10% by weight of an 
unsaturated monomer containing at least one carboxyl group, and 
copolymerizing these with at least one radically polymerizable monomer to 
give an acrylic copolymer (base resin). At least a part of the carboxyl 
groups of the so obtained resin is then reacted with the glycidyl groups 
of a glycidyl group-containing unsaturated monomer to give an acrylic 
resin having a neutralizable tertiary amino group or both the tertiary 
amino group and a carboxyl group. This resin can be used as a cationic or 
amphoteric dispersion stabilizer. 
The carboxyl group-containing monomers used in the synthesis of the 
aforesaid acrylic resin include, for example acrylic acid, methacrylic 
acid and crotonic acid. On the other hand, as the unsaturated monomer 
containing the tertiary amino group, included are the N,N-disubstituted 
aminoalkyl(meth)acrylates such as N,N-dimethylaminoethyl(meth)acrylate and 
N,N-diethylaminoethyl(meth)acrylate. 
As the radically polymerizable acrylic monomers that can be copolymerized 
with these neutralizable group-containing monomers, usable are those that 
have been used heretofore in preparing the acrylic polymers by the radical 
polymerization method. Examples of these monomers are the C.sub.1-18 alkyl 
esters of acrylic acid or methacrylic acid such as methyl acrylate, ethyl 
acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, hexyl 
acrylate, octyl acrylate, lauryl acrylate, methyl methacrylate, ethyl 
methacrylate, propyl methacrylate, isopropyl methacrylate, butyl acrylate, 
hexyl methacrylate, octyl methacrylate and lauryl methacrylate; C.sub.2-8 
hydroxyalkyl esters of acrylic acid or methacrylic acid such as 
hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate 
and hydroxypropyl methacrylate; acrylonitrile and methacrylonitrile. 
These radically polymerizable acrylic monomers can be used either singly or 
in combinations of two or more. As required, a part of the acrylic monomer 
may be substituted by other radically polymerizable monomers, for example 
an aromatic vinyl compound such as styrene, alpha-methylstyrene, or 
vinyltoluene. 
The aforementioned carboxyl-containing unsaturated monomer, tertiary amino 
group-containing unsaturated monomer and radically polymerizable acrylic 
monomer can be copolymerized by a method known per se such as the solution 
or emulsion polymerization technique. 
The introduction of a polymerizable double bond to the aforesaid acrylic 
copolymer that is used as the base of the dispersion stabilizer resin can 
usually be accomplished as described hereinbefore by reacting a glycidyl 
group-containing unsaturated monomer (e.g. glycidyl acrylate, glycidyl 
methacrylate or allylglycidyl ether) with the carboxyl group which is the 
neutralizable group. In addition to this method, in such a case where the 
acrylic copolymer has a hydroxyl group besides the carboxyl group and/or 
tertiary amino group, the introduction of the polymerizable double bond 
can also be performed by reacting hydroxyl group of said copolymer with an 
isocyanate group of an equimolar adduct of a diisocyanate compound (e.g. 
tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate of isophorone 
diisocyanate) with a hydroxyl group-containing unsaturated monomer (e.g. 
hydroxyethyl acrylate or hydroxyethyl methacrylate). In the latter case, 
the acrylic copolymer should desirably contain as its constituent 
component at least 1% by weight, preferably 2 to 40% by weight, of the 
hydroxyl group-containing acrylic monomer unit. 
Alternatively, the polymerizable double bond can also be introduced to the 
base resin by a procedure comprising introducing in advance an epoxy group 
to the carboxyl group and/or tertiary amino group-containing acrylic 
copolymer which is the base resin (for example, by using a glycidyl 
group-containing unsaturated monomer as one of the monomers in preparing 
the acrylic copolymer), and thereafter reacting an unsaturated acid such 
as acrylic acid or methacrylic acid with the epoxy group. In this case, 
the acrylic copolymer should desirably contain at least 1% by weight, 
preferably 2 to 40% by weight, of such a glycidyl group-containing 
unsaturated monomer unit as its constituent component. 
Conveniently usable as the acrylic resin in step (a) of this invention is 
one having in general a weight average molecular weight of about 5000 to 
about 50,000 (number average molecular weight of about 1000 to about 
30,000), preferably about 5000 to about 20,000. When the molecular weight 
is less than about 5000, the stability of the dispersed particles in the 
solvent is poor, and there is a tendency to flocculation or sedimentation 
of the particles. On the other hand, when the molecular weight exceeds 
about 50,000, a marked increase in viscosity takes place, with the 
consequence that there is the possibility that difficulty is experienced 
in the handling of the resin. 
(B) Polyester Resins and Alkyd Resins 
The polyester resins and alkyd resins usable in step (a) of this invention 
can be prepared, for example by directly reacting a glycidyl 
group-containing unsaturated monomer, such as hereinbefore described, with 
a part of the carboxyl groups of polyester or alkyd resins having carboxyl 
groups in their terminal or side chain. On the other hand, the 
introduction of the polymerizable double bond can also be performed by 
reacting the hydroxyl groups possibly present in the polyester or alkyd 
resins with either an equimolar adduct of a diisocyanate and a hydroxyl 
group-containing unsaturated monomer, such as described in (A), above, or 
isocyanate ethyl(meth)acrylate. 
The polyester of alkyd resins having carboxyl groups in their terminal or 
side chain should desirably have a resin acid value of usually at least 
20, preferably 40 to 70. Even in the case of the polyester or alkyd resins 
having a low resin acid value of less than 20, they can be used as the 
above-described starting material by increasing the resin acid value by 
the introduction of the carboxyl groups by reacting an acid anhydride such 
as phthalic anhydride or trimellitic anhydride with the hydroxyl groups 
present in the resins. 
The term "resin acid value", as used herein, denotes the number of 
milligrams of KOH required for neutralizing 1 gram of resin. 
The above-mentioned base the polyester or alkyd resins functions as a 
dispersion stabilizer for an anionic aqueous dispersion on being 
neutralized in the hereinbelow-described step (b). (C) Other resins. 
As other dispersion stabilizer resins that can be used in step (a) of this 
invention, there can be mentioned, for example the block or graft 
copolymers having a polymerizable double bond, which copolymers are 
comprised, for example of a first segment having a sufficient amount of 
neutralizable groups to render the polymer into an emusifiably dispersed 
or dissolved state when neutralized and a second segment substantially 
free of neutralizable groups; an example being the grafted product of a 
carboxyl group-containing acrylic polymer and a cellulose derivative, to 
which has been introduced a polymerizable double bond. These are resins 
that can also be suitably used in this invention. 
The graft copolymer can be obtained in the following manner. A vinyl 
monomer mixture containing acrylic acid or methacrylic acid as its 
indispensable components is polymerized in the presence of a cellulose 
derivative such as cellulose acetate butyrate using a polymerization 
initiator such as benzoyl peroxide or tert-butylhydroperoxide to give a 
carboxyl group-containing grafted product, after which a glycidyl 
group-containing unsaturated monomer such as mentioned hereinbefore is 
caused to react with a part of the carboxyl groups of the grafted product. 
When polymer particles are formed in a water-insoluble medium using this 
dispersion stabilizer and then the particles are caused to migrate to an 
aqueous medium, the water-insoluble cellulose portion becomes deposited on 
the surface of the polymer particles, and there thus can be formed a 
dispersion of greater stability. 
As indicated hereinbefore, the dispersion stabilizer resin such as 
described above has at least 0.3 unit of a polymerizable double bond in 
each of its molecules. Hence, when a radically polymerizable monomer is 
polymerized in the presence of this dispersion stabilizer resin, the 
double bond becomes a linkage site of a graft or block to the dispersed 
particles, and it is presumed that at least 30% by weight of the 
dispersion stabilizer resin becomes linked as a graft or block to the 
surface of the dispersed polymer particles. 
The dispersion stabilizer resins used in this invention can be used either 
singly or in combination of two or more classes. Further, they may also be 
used conjointly with a small amount of other dispersion stabilizers, for 
example the butyl etherized melamine-formaldehyde resin, air-dryable alkyd 
resin, or a graft resin obtained by polymerizing methyl methacrylate to an 
adduct of a self-condensed product of 12-hydroxystearic acid and glycidyl 
(meth)acrylate. 
In accordance with step (a) of this invention, at least one radically 
polymerizable monomer is polymerized in an organic liquid in the presence 
of a dispersion stabilizer resin such as described above. 
As the organic liquid to be used in the aforesaid polymerization reaction, 
included are those organic liquids that are substantially immiscible with 
water and do not substantially dissolve the dispersed polymer particles 
formed by the polymerization reaction but are good solvents for the 
dispersion stabilizer resin and the radically polymerizable monomer. 
Specific examples of such organic liquids are the aliphatic hydrocarbons 
such as hexane, heptane and octane; aromatic hydrocarbons such as benzene, 
toluene and xylene; or solvents of the alcohol, ether, ester and ketone 
types, in which the solubility in water at 20.degree. C. is not more than 
5 g, preferably not more than 2 g, per 100 g or the solubility of water in 
the organic liquid at 20.degree. C. is not more than 10 g, preferably not 
more than 5 g per 100 g, examples being octyl alcohol, methyl isobutyl 
ketone, diisobutyl ketone, ethyl acyl ketone, methyl hexyl ketone, ethyl 
butyl ketone, ethyl acetate, isobutyl acetate, acyl acetate and 
2-ethylhexylacetate. These organic liquids may be used either singly or as 
a mixture of two or more but, in general, conveniently used is a 
combination consisting predominantly of an aliphatic hydrocarbon suitably 
combined with an aromatic hydrocarbon or a solvent of the alcohol, ether, 
ester or ketone type such as indicated above. 
If a medium consisting of only an organic liquid having a lower boiling 
point than water (e.g. hexane, heptane, toluene, etc.) is used as the 
organic liquid, the replacement with an aqueous medium is not only 
facilitated but can be carried out substantially completely in the 
subsequent step (c). It thus becomes possible to prepare an aqueous 
dispersion substantially free of an organic liquid. 
On the other hand, when there is used as the organic liquid a mixture of a 
water-immiscible organic liquid having a boiling point lower than water 
and not more than about 30% by weight of a water-immiscible organic liquid 
having a boiling point higher than water (e.g. 2-ethylhexyl alcohol, 
n-octyl alcohol, benzyl alcohol, methyl isobutyl ketone, cyclohexanone, 
isophorone, terpentine oil, mineral spirit, etc.), the latter organic 
liquids can be made to remain on the surface or inside of the polymer 
particles even after the subsequent step in which they have been replaced 
with water, and consequently the access or permeation of water to the 
surface or interior of the polymer particles is hampered. Hence, the 
hydrolysis of the dispersed polymer can be prevented. A further feature is 
that when this aqueous dispersion is used in a coating material the 
evaporation of water is fast, and hence the coating material possesses 
superior drying property. 
In a similar manner as with the foregoing water-immiscible organic liquids 
having a boiling point higher than water, the addition in small amounts of 
a plasticizer, degradation preventive agent (antioxidant, ultraviolet 
absorber, etc.) and curing catalyst makes it possible to deposit these 
additives on the surface or inside the resulting dispersed polymer 
particles. 
Further, it is also possible to make conjoint use as the organic liquid in 
an amount not exceeding 50% by weight of a so-called water-soluble or 
hydrophilic organic liquid that is completely soluble in water or can be 
dissolved to a considerable degree. As this kind of organic liquid, 
included are those whose solubility in water at 20.degree. C. is at least 
5 g/100 g, examples of which are alcohols such as methanol, ethanol, 
isopropanol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol and 
sec-butyl alcohol; and ethereal alcohol such as methyl cellosolve, 
cellosolve, isopropyl cellosolve, butyl cellosolve and diethylene glycol 
monobutyl ether. 
The use of such water-soluble or hydrophilic organic liquids makes it 
possible to add the organic liquid dispersion to the aqueous medium in an 
optional proportion. Hence, the preparation of the aqueous dispersion is 
facilitated. Further, when an aqueous dispersion obtained by the use of a 
mixture of a low-boiling hydrophilic organic liquid and water is used as a 
coating material, there is obtained the effect that the evaporation of 
water at the time of application can be accelerated. There is also the 
advantage that since the solubility of the dispersion stabilizer resin is 
increased the choice of the dispersion stabilizer resin can be made from a 
wider range of resins. 
There is imposed no particular restriction as to the monomers that are 
polymerized in the presence of the dispersion stabilizers and organic 
liquids described hereinbefore so long as they are radically polymerizable 
monomers. Various kinds can be used, typical examples of which are as 
follows: 
(a) Esters of acrylic acid and methacrylic acid: for example the C.sub.1-18 
alkyl esters of acrylic acid and methacrylic acid such as methyl acrylate, 
ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, hexyl 
acrylate, octyl acrylate, lauryl acrylate, methyl methacrylate, ethyl 
methacrylate, propyl methacrylate, isopropyl methacrylate, butyl 
methacrylate, hexyl methacrylate, octyl methacrylate and lauryl 
methacrylate; glycidyl acrylate and glycidyl methacrylate; C.sub.2-8 
alkenyl esters of acrylic acid or methacrylic acid such as allyl acrylate 
and allyl methacrylate; C.sub.2-8 hydroxyalkyl esters of acrylic acid or 
methacrylic acid such as hydroxyethyl acrylate, hydroxyethyl methacrylate, 
hydroxypropyl acrylate and hydroxypropyl methacrylate; and C.sub.3-18 
alkenyloxyalkyl esters of acrylic acid or methacrylic acid such as 
allyloxyethyl acrylate and allyloxyethyl methacrylate. 
(b) Aromatic vinyl compounds: for example styrene, alpha-methylstyrene, 
vinyltoluene, p-chlorostyrene and vinylpyridine. 
(c) Alpha,beta-ethylenically unsaturated acids: for example acrylic acid, 
methacrylic acid and itaconic acid. 
(d) Others: acrylonitrile, methacrylonitrile, methyl isopropenyl ketone; 
vinyl acetate, Veoba monomer (a product of Shell Chemical Company), vinyl 
propionate, vinyl pivalate, etc. 
Monomers and monomeric mixtures containing at least 40% by weight of an 
ester of acrylic acid or methacrylic acid are especially suitable of these 
monomers. 
The polymerization of the foregoing monomers is carried out using a radical 
polymerization initiator. Usable radical polymerization initiators 
include, for example the azo-type initiators such as 
2,2'-azoisobutyronitrile and 2,2'-azobis(2,4-dimethylvaleronitrile); and 
the peroxide-type initiators such as benzoyl peroxide, lauryl peroxide and 
tert-butyl peroctoate. These polymerization initiators can be used in an 
amount ranging from 0.5 to 10 parts by weight, preferably 0.5 to 5 parts 
by weight, per 100 parts by weight of the monomer used in the 
polymerization reaction. 
While the amount used of the dispersion stabilizer resin varies widely 
depending upon the class of the resin, usually an amount ranging from 3 to 
70% by weight, preferably 5 to 45% by weight, based on the total amount of 
the monomer to be polymerized and the dispersion stabilizer resin is 
conveniently used. 
Further, it is desired that the total concentration of the monomer and the 
dispersion stabilizer in the organic liquid be usually from 30 to 70% by 
weight, and preferably from 30 to 60% by weight. 
The polymerization reaction can be carried out by methods known per se. The 
reaction temperature at the time of the polymerization reaction generally 
ranges from 60.degree. to 160.degree. C., and the reaction can be usually 
completed in 1 to 15 hours. 
There is thus obtained an organic liquid dispersion of polymer particles 
which consists of a dispersion in an organic liquid of polymer particles 
to whose surface has been grafted or linked as blocks a dispersion 
stabilizer resin. 
In step (b) of this invention the neutralizable groups of the dispersion 
stabilizer resin are neutralized. When the neutralizable group is an acid 
group such as the carboxyl group, usable as the neutralizing agent are 
ammonia and the bases such as dimethylaminoethanol, methylamine, 
dimethylamine, ethylamine, diethylamine, triethylamine, 
diethylaminoethanol, diethanolamine and triethanolamine. When the 
neutralizable group is a basic group such as the tertiary amine group, the 
acids such as lactic acid, acetic acid, formic acid, propionic acid, 
hydroxyacetic acid, phosphoric acid and hydrochloric acid are used. 
The neutralization is usually carried out on the dispersion stabilizer 
resin present at the surface of the dispersed particles of polymer 
prepared in step (a). The neutralization is performed to such a degree 
that the dispersion stabilizer resin used in step (a) emulsifiably 
disperses or dissolves in an aqueous medium. Specifically, the 
neutralization treatment is suitably carried out by adding the aforesaid 
neutralizing agents in an amount of about 0.5 to about 1.2 equivalents per 
equivalent of the neutralizable groups present in the resin. 
The neutralizing step can be carried out by adding the neutralizing agent 
to the organic liquid dispersion of polymer particles obtained in step 
(a). At times, it may also be carried out after having replaced at least a 
part of the organic liquid of the dispersion with an aqueous medium. 
While it is preferred in this invention that the neutralization of the 
neutralizable groups of the dispersion stabilizer resin be performed 
following step (a), it is also possible to use as the dispersion 
stabilizer resin in step (a) one whose neutralizable groups have already 
been neutralized with an acid or base prior to the polymerization reaction 
of step (a). 
The replacement of the organic liquid with an aqueous medium (i.e. the 
conversion of the dispersion medium) in step (c) of this invention is 
usually carried out in the following manner. The organic liquid dispersion 
of polymer particles obtained from the steps described hereinbefore is 
subjected to reduced pressure to remove at least a part of the organic 
liquid from the dispersion. This is followed by the addition of water and 
thorough stirring and, as required, further removal of at least a part of 
the remaining organic liquid under reduced pressure. 
On the other hand, when it is desired to remove the organic liquid 
virtually completely from the aqueous medium, the conversion of the 
dispersion medium can be carried out by suitably choosing the organic 
liquid and performing the azeotropic distillation of water and the organic 
liquid. 
Further, the conversion of the dispersion medium can also be performed in 
the following manner. After having performed the neutralization in 
accordance with step (b) of this invention, the organic liquid is 
completely removed under reduced pressure or by heating to yield a product 
as a dry powder, following which this powder is redispersed in an aqueous 
medium. 
The aqueous dispersion of polymer particles prepared by the process of this 
invention described hereinbefore has an extremely superior dispersion 
stability and can be used in such applications as coating materials, 
molded articles, adhesives, fillers, etc. 
While the aqueous dispersion provided by this invention can be used as 
such, it can also be incorporated with colorants, plasticizers, curing 
agents, etc., as required. The colorants include dyestuffs and organic and 
inorganic pigments. As plasticizers, those known, for example the 
low-molecular-weight plasticizers such as dimethyl phthalate and dioctyl 
phthalate, and the high-molecular-weight plasticizers such as the vinyl 
polymer-type plasticizers and the polyester-type plasticizers can be used. 
These plasticizers can be used by mixing them in advance in the dispersion 
liquid, or they can be incorporated in the dispersed polymer particles by 
dissolving them in the radically polymerizable monomer at the time of 
preparing the dispersion. On the other hand, usable as the curing agents 
are such crosslinking agents as the amino resins and epoxy resins.

The following examples and comparative examples will serve to illustrate 
the present invention more specifically. In the examples and comparative 
examples the parts and percentages are all on a weight basis. 
EXAMPLE 1 
Synthesis of Dispersion Stabilizer (A) 
Seventy parts of isopropyl alcohol and 30 parts of butyl cellosolve were 
heated under reflux, after which the following monomers and polymerization 
initiator were added dropwise over the course of 3 hours. 
______________________________________ 
Parts 
______________________________________ 
Styrene 15 
n-Butyl methacrylate 20 
Lauryl methacrylate 43 
2-Hydroxyethyl methacrylate 
15 
Methacrylic acid 7 
2,2'-Azobisisobutyronitrile 
2 
______________________________________ 
After completion of the addition, the reaction mixture was aged for 2 
hours. The resulting acrylic resin varnish had a nonvolatile matter 
content of 50%, a viscosity (Gardener, 25.degree. C.; applies equally 
hereinafter) of N, and a weight average molecular weight of about 15,000. 
This was followed by the addition of 1 part of glycidyl methacrylate, 0.02 
part of 4-tert-butyl pyrocatechol and 0.1 part of dimethylaminoethanol to 
the total amount of the foregoing varnish, after which the mixture was 
reacted under reflux for 5 hours to introduce a copolymerizable double 
bond into the molecular chain of the dispersion stabilizer. On measurement 
of the resin acid value, the number of double bond introduced was found to 
be about 0.7 unit per molecular chain. 
Synthesis of Dispersed Polymer 
One hundred parts of heptane and 50 parts of the dispersion stabilizer (A) 
were charged to a flask and refluxed at about 98.degree. C., after which 
the following monomers and polymerization initiator were added dropwise 
over the course of 4 hours. 
______________________________________ 
Parts 
______________________________________ 
Styrene 15 
Methyl methacrylate 45 
Acrylonitrile 25 
2-Hydroxyethyl methacrylate 
15 
2,2'-Azoisobutyronitrile 
1 
______________________________________ 
After completion of the addition, the reaction mixture was aged for 2 
hours. There was thus obtained a milky white stable dispersion of polymer 
particles of low viscosity having a nonvolatile matter content of 50%, a 
viscosity of B and particle diameter of 0.2 to 0.4 micron (as determined 
by an electron microscope; applies equally hereinafter). 
Conversion to an Aqueous Medium 
One hundred parts of the polymer dispersion and 0.7 part of 
dimethylaminoethanol were charged to a flask and thoroughly stirred. The 
mixture was then heated at about 80.degree. C., and the solvent was 
recovered under reduced pressure. After concentrating the polymer 
dispersion until its solids content reached 70%, 50 parts of distilled 
water was added, and while the mixture was being thoroughly stirred, it 
was heated up to 90.degree. C., and further recovery of the solvent was 
carried out under reduced pressure. The thus obtained aqueous dispersion 
had a solids content of 45%, and the composition of the aqueous medium at 
this time was as follows: 
The resulting aqueous dispersion had a viscosity of H and a particle 
diameter of 0.2 to 0.4 micron. There was no difference in the particle 
diameter between this aqueous dispersion and the dispersion in the organic 
medium. The resulting dispersion was left standing for one month at room 
temperature, but there was seen no formation of any sediment and no 
occurrance of coarse particles. 
______________________________________ 
Parts 
______________________________________ 
Water 82 
Isopropyl alcohol 
8 
Butyl cellosolve 10 
Heptane trace 
______________________________________ 
EXAMPLE 2 
One hundred parts of isopropyl alcohol and 50 parts of dispersion 
stabilizer (A) were charged to a flask, and while maintaining a reflux 
temperature of 83.degree. C., the following monomers and polymerization 
initiator were added dropwise over the course of 4 hours. 
______________________________________ 
Parts 
______________________________________ 
Acrylonitrile 50 
Methyl methacrylate 25 
Styrene 10 
2-Hydroxyethyl methacrylate 
15 
2,2'-Azoisobutyronitrile 
1.5 
______________________________________ 
After completion of the addition, the reaction mixture was aged for 2 
hours. Dimethylaminoethanol (2 parts) was then added, and the mixture was 
stirred. This was followed by the addition of 125 parts of distilled 
water, and while heating the mixture the organic solvent was recovered 
under reduced pressure at 80.degree. to 90.degree. C. 
The thus obtained aqueous dispersion was of a somewhat yellowish creamy 
color and had a solids content of 45%, a viscosity of J and a particle 
diameter of 0.3 to 0.5 micron. 
The composition of this aqueous medium was as follows: 
______________________________________ 
Parts 
______________________________________ 
Water 82 
Isopropyl alcohol 
8 
Butyl cellosolve 10 
______________________________________ 
EXAMPLE 3 
Seventy parts of heptane, 30 parts of isopropyl alcohol, 50 parts of 
dispersion stabilizer (A), 1 part of dimethylaminoethanol and 15 parts of 
butylated melamine resin (Uban 20 SE, a product of Mitsui Toatsu 
Chemicals, Inc., 60% solution) were charged to a flask, and while 
maintaining a reflux temperature the following monomers and polymerization 
initiator were added dropwise over the course of 3.5 hours. 
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Parts 
______________________________________ 
Styrene 15 
Methyl methacrylate 45 
Acrylonitrile 25 
2-Hydroxypropyl methacrylate 
15 
2,2'-Azoisobutyronitrile 
1.5 
______________________________________ 
After completion of the addition, the reaction mixture was aged for 2 
hours. 2-Dimethylaminoethanol (1 part) was further added followed by 
stirring the mixture. Water (135 parts) at about 65.degree. C. was then 
added, and while slowly heating the mixture heptane and isopropyl alcohol 
were recovered under reduced pressure. 
The resulting aqueous dispersion had a solids content of 42.5% and a 
viscosity of L. Even though this dispersion was let standing for one month 
at room temperature, it was stable, there being seen no formation of any 
sediment. 
The composition of this aqueous medium was as follows: 
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Parts 
______________________________________ 
Water 74.5 
Isopropyl alcohol 
13.8 
Butyl cellosolve 8.3 
Butyl alcohol 2.3 
Xylol 0.1 
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When this aqueous dispersion was coated on a sheet glass and heated at 
140.degree. C. for 30 minutes, a transparent, highly glossy and hard 
crosslinked coated film having a gel fraction of 97% was obtained. 
EXAMPLE 4 
One hundred parts of heptane, 50 parts of dispersion stabilizer (A) and 1 
part of 2-dimethylaminoethanol were charged to a flask, and while 
maintaining a reflux temperature of 980.degree. C. the following monomers 
and polymerization initiator were added dropwise over the course of 4 
hours. 
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Parts 
______________________________________ 
2-Hydroxyethyl acrylate 
68 
Methyl acrylate 25 
1,6-Hexanediol diacrylate 
5 
Methacrylic acid 2 
2,2'-Azoisobutyronitrile 
1 
______________________________________ 
After completion of the addition, the reaction mixture was aged for 2 
hours. After the addition further of 1 part of dimethylaminoethanol, 125 
parts of distilled water was added, following which the reaction mixture 
was heated, and the organic solvent was recovered under reduced pressure. 
The resulting aqueous dispersion had a solids content of 45% and a 
viscosity of N. The particles were crosslinked, and even though a large 
amount of acetone was added, the particles were not dissolved. 
EXAMPLE 5 
Synthesis of Dispersion Stabilizer (B) 
Seventy parts of toluene and 30 parts of octyl alcohol were refluxed, and 
then the following monomers and polymerization initiator were added 
dropwise over the course of 3 hours. 
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Parts 
______________________________________ 
Styrene 15 
n-Butyl methacrylate 40 
Lauryl methacrylate 35 
Dimethylaminoethyl methacrylate 
9 
Acrylic acid 1 
2,2'-Azoisobutyronitrile 
2 
______________________________________ 
After completion of the addition, the reaction mixture was aged for 2 
hours. To the total amount of the resulting copolymer resin varnish were 
then added 1 part of glycidyl methacrylate and 0.02 part of 
4-tert-butylpyrocatechol, after which a reflux reaction was continued for 
5 hours. The polymerizable double bond introduced amounted to about 0.7 
unit per molecular chain. 
Synthesis of Dispersed Polymer 
One hundred parts of heptane and 50 parts of dispersion stabilizer (B) were 
charged to a flask, and while maintaining a reflux temperature the 
following monomers and polymerization initiator were added dropwise over 
the course of 4 hours. 
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Parts 
______________________________________ 
Styrene 15 
Methyl methacrylate 45 
Acrylonitrile 25 
2-Hydroxyethyl methacrylate 
15 
Tert-butyl peroctoate 
1.5 
______________________________________ 
After completion of the addition, the reaction mixture was aged for 2 
hours. The resulting liquid was a yellowish dispersion. After adding 2.7 
parts of acetic acid to this dispersion, the heptane and toluene were 
recovered at reduced pressure until the solids content became about 70%. 
This was followed by carrying out the further recovery of the solvents by 
adding 150 parts of hot water at about 80.degree. C. Water recovered at 
the same time was returned to the system to adjust the solids content to 
45%. 
The composition of the aqueous medium of the aqueous dispersion was as 
follows: 
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Parts 
______________________________________ 
Water 90 
Octyl alcohol 
10 
Heptane trace 
Toluene trace 
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This dispersion contained about 5.5% of octyl alcohol, but it was stable, 
there being no sedimentation of particles nor separation of the organic 
solvents even after it was left standing for one month. 
EXAMPLE 6 
Fifty parts of the dispersion stabilizer (A) obtained in Example 1, 1.7 
parts of dimethylaminoethanol and 100 parts of heptane were charged to a 
flask, and the dispersion stabilizer (A) was neutralized with stirring. 
The contents were then refluxed at about 98.degree. C., and the following 
monomers and polymerization initiator were added dropwise over the course 
of 4 hours. 
______________________________________ 
Parts 
______________________________________ 
Styrene 15 
Methyl methacrylate 45 
Acrylonitrile 25 
2-Hydroxyethyl methacrylate 
15 
2,2'-Azoisobutyronitrile 
1 
______________________________________ 
After completion of the addition, the reaction mixture was aged for 2 
hours. As in Example 1, the resulting liquid was a milky white, stable low 
viscosity polymer dispersion. This dispersion was then heated at about 
80.degree. C., and the solvents were recovered under reduced pressure 
followed by concentrating the dispersion until its solids content became 
70%. This was followed by the addition further of 50 parts of distilled 
water, heating the dispersion up to 90.degree. C. with thorough stirring, 
and recovering the solvents further under reduced pressure to give an 
aqueous dispersion having a solids content of 45%. The aqueous dispersion 
thus obtained was the same as that of Example 1. 
COMATIVE EXAMPLE 1 
An organic liquid dispersion of polymer particles was prepared in the same 
manner as in Example 1 but using as the dispersion stabilizer one that had 
been synthesized without introducing glycidyl methacrylate into the 
molecular chain during the step of synthesizing the dispersion stabilizer 
(A). The organic liquid dispersion thus obtained was relatively stable, 
and there was seen no sedimentation even after it was left standing for 
one month. However, when the organic liquid of this dispersion was 
replaced with an aqueous medium as in Example 1, the resulting aqueous 
dispersion, after standing for one week, separated into two layers, a 
transparent supernatant portion and a sedimental portion, and the lower 
layer became pasty like pudding. 
COMATIVE EXAMPLE 2 
An aqueous dispersion was prepared in the same manner as in Example 4 using 
the same monomeric composition but without using 1,6-hexanediol 
diacrylate. In this case the viscosity of the whole system increased to 
become a puddinglike semisolid product. These particles were completely 
soluble in acetone.