Stable amphoteric aqueous dispersions of synthetic polymers

Stable amphoteric aqueous dispersions of synthetic polymers obtained by reacting at least one unsaturated nitrogen compound capable of being hydrolyzed in an acid or alkaline medium with an aqueous emulsion reaction mixture, containing cationic species, of at least one non-ionic monomer capable of being copolymerized with the nitrogen compound to form synthetic polymers and at least one substance which generates cationic species capable of chemically binding with the synthetic polymers.

FIELD OF THE INVENTION 
This invention relates to stable amphoteric aqueous dispersions of 
synthetic polymers obtained by reacting at least one unsaturated nitrogen 
compound capable of being hydrolyzed in an acid or alkaline medium with an 
aqueous emulsion reaction mixture. A process for making the aqueous 
dispersions of the claimed invention and a composition capable of forming 
the aqueous dispersions are also disclosed. 
BACKGROUND OF THE INVENTION 
It is known in the art that amphoteric latices can be prepared by aqueous 
emulsion polymerization. U.S. Pat. No. 3,404,114 discloses the preparation 
of amphoteric latices by (1) heating an aqueous system with polymerization 
catalyst and an emulsifier; (2) adding to the aqueous system an 
unsaturated carboxylic acid monomer and an unsaturated acid ester monomer; 
(3) neutralizing the mixture to a pH of about 7 with a neutralizing agent 
containing nitrogen; and (4) adding to the aqueous system an alkyl amino 
alkyl ester of an unsaturated acid monomer from the mixture. 
Though this process produces stable latices, an appreciable percentage of 
undesirable grains accumulate during the polymerization or neutralization 
of the aqueous dispersion due to the instability of the polymer particles. 
These grains cause low filtration yields which lead to increased 
production costs, and the grains also decrease the quality of the 
dispersions. 
The present invention addresses these difficulties by eliminating the 
intermediate neutralization stage, thereby producing stable amphoteric 
aqueous dispersions of synthetic polymers with less than 500 parts per 
million of undesirable grains, (about 0.05 percent of undesirable grains 
by weight of polymer). As used herein, the term undesirable grains refers 
to the total amount of grains which are retained after sifting the grains 
through a mesh screen of 40.mu. wide and a mesh screen 100.mu. wide. 
SUMMARY OF THE INVENTION 
The present invention provides a process for making stable amphoteric 
aqueous dispersions of synthetic polymers comprising the steps of 
providing at least one unsaturated nitrogen compound capable of being 
hydrolyzed in an acid or alkaline medium and reacting the nitrogen 
compound with an aqueous emulsion reaction mixture containing cationic 
species, of at least one non-ionic monomer, capable of being copolymerized 
with the hydrolyzable unsaturated nitrogen compound to form synthetic 
polymers, and at least one substance which generates cationic species 
capable of chemically binding with the synthetic polymers. 
The invention also includes both the stable amphoteric aqueous dispersions 
of synthetic polymers obtained by reacting an unsaturated nitrogen 
compound with an aqueous emulsion reaction mixture containing cationic 
species, and a composition capable of forming stable amphoteric aqueous 
dispersions comprising an unsaturated nitrogen compound and an aqueous 
emulsion reaction mixture.

DETAILED DESCRIPTION OF THE INVENTION 
In accordance with the invention as embodied herein, the stable amphoteric 
aqueous dispersions of synthetic polymers can be made by providing at 
least one unsaturated nitrogen compound capable of generating anionic 
changes by partial or total hydrolysis in a basic medium, and reacting the 
nitrogen compound with an aqueous emulsion reaction mixture, containing 
cationic species. The aqueous emulsion reaction mixture contains at least 
one non-ionic monomer capable of being copolymerized with the nitrogen 
compound and at least one substance which generates cationic species. The 
substance is selected from the group consisting of a polymerization 
initiator which generates radicals with cationic extremities, an 
unsaturated salt of a polycoordinated onium of a group 5a or 6a element 
capable of copolymerizing with the monomer, and mixtures thereof. The 
amount of the substance which generates cationic species corresponds to a 
ratio of the number of cationic charges generated by said substance to the 
number of anionic charges generated by said nitrogen compound in a basic 
medium, of less than 1. 
The invention also includes stable amphoteric aqueous dispersions of 
synthetic polymers obtained by reacting at least one unsaturated nitrogen 
compound capable of being hydrolyzed in an acid or alkaline medium, with 
an aqueous emulsion reaction mixture, containing cationic species, of at 
least one non-ionic monomer capable of being copolymerized with the 
nitrogen compound to form synthetic polymers and at least one substance 
which generates cationic species capable of chemically binding with the 
synthetic polymers. 
The invention further embodies a composition capable of forming stable 
amphoteric aqueous dispersions of synthetic polymers comprising at least 
one unsaturated nitrogen compound capable of being hydrolyzed in an acid 
or alkaline medium and an aqueous emulsion reaction mixture, containing 
cationic species, of at least one non-ionic monomer capable of being 
copolymerized with the nitrogen compound to form synthetic polymers and at 
least one substance which generates cationic species capable of chemically 
binding with the synthetic polymers. 
The unsaturated nitrogen compound is considered partially hydrolyzable if 
it has at least about a 10% hydrolysis level when polymerized in an acid 
or alkaline medium. For example, those compounds which correspond to the 
following general formula may be used in preparing the aqueous dispersions 
of the present invention: 
##STR1## 
where, R.sub.1 is a hydrogen atom or a methyl group, R.sub.2 is a 
methylene or an ethylene group, R.sub.3 is a hydrogen atom or a linear 
alkyl group with 1 to 4 carbon atoms, and R'.sub.3 is either a hydrogen 
atom or a linear alkyl group with 1 to 4 carbon atoms or, if R.sub.3 is a 
hydrogen atom, a branched alkyl group with 3 or 4 carbon atoms, with the 
total number of carbon atoms in groups R.sub.2, R.sub.3, and R'.sub.3 
being less than or equal to 8, preferably less than equal to 6. 
Examples of such compounds are dimethylaminomethyl acrylate or 
methacrylate, dimethyulaminoethyl acrylate or methacrylate, 
tert-butylaminomethyl acrylate or methacrylate, and tert-butylaminoethyl 
acrylate or methacrylate. 
Typical non-ionic monomers which may be employed in the process of the 
present invention include vinylaromatic compounds, such as styrene, 
.alpha.-methylstyrene, vinyltoluene and monochlorostyrene, vinyl esters, 
such as vinyl acetate, vinyl propionate, vinyl versatate and vinyl 
butyrate, ethylenic nitriles, such as acrylonitrile and methacrylonitrile, 
ethylenic carboxylic esters, such as methyl, ethyl, propyl, isopropyl, 
butyl, 2-ethylhexyl, hydroxyethyl, hydroxypropyl or glycidyl acrylate, 
methyl, ethyl, propyl, butyl, hydroxyethyl, hydroxypropyl, or glycidyl 
methacrylate, dialkyl esters of ethylenic dicarboxylic acids, such as 
dialkyl esters of fumaric acid, maleic acid and itaconic acid, and 
ethylenic amides and the N-substituted derivatives of ethylenic amides 
such as acrylamide, methacrylamide, and N-methylol and 
N-methoxy-methyl-acrylamide and -methacrylamide. These non-ionic monomers 
may be used individually or, if they are capable of being copolymerized 
with one another, as a mixture of 2 or more. 
The substance which generates cationic species must be either 
non-hydrolyzable or partially hydrolyzable. In other words, the substance 
must have a hydrolysis level of less than or equal to 50%. For example, 
polymerization initiators which produce radicals with cationic 
extremities, such as 2,2'-azobis-(2-amidinopropane) hydrochloride and 
azo-bis-N,N'-dimethyleneisobutyramidine hydrochloride, unsaturated salts 
of a polycoordinated onium of a group 5a or 6a element (nitrogen, 
phosphorous or sulfur) capable of being copolymerized with the non-ionic 
monomer, and mixtures thereof may be used as the substance which generate 
cationic species. As used in this specification and the claims, any salt 
containing an onium cation, with all of the group 5a or 6a element 
valences satisfied by hydrocarbon groupings, at least one of which 
hydrocarbon groupings is unsaturated, and the free valency of the group 5a 
or 6a element is saturated by a carbon atom is considered an unsaturated 
salt of a polycoordinated onium of a group 5a or 6a element. 
Exemplary of such unsaturated salts are the unsaturated quaternary ammonium 
salts having the formula: 
##STR2## 
where X.sup.- is Cl.sup.-, Br.sup.-, I.sup.-, SO.sub.4 H.sup.-, 
SO.sub.4.sup.--, CH.sub.3 SO.sub.4.sup.-, C.sub.2 H.sub.5 SO.sub.4.sup.-, 
or CH.sub.3 COO.sup.-, R.sub.4 is a hydrogen atom or a methyl group, A is 
an oxygen atom or an --NH-- group, R.sub.5 is a linear or branched 
alkylene group with 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, 
and R.sub.6, R'.sub.6, and R".sub.6, which may be identical or different, 
are either an alkyl group with 1 to 4 carbon atoms, optionally substituted 
by a hydroxyl radical, or a phenyl group, optionally substituted by an 
alkyl radical with 1 to 9 carbon atoms, wherein the total number of carbon 
atoms in groups R.sub.5, R.sub.6, R'.sub.6, and R".sub.6 is greater than 4 
if A is oxygen. 
Examples of such quaternary ammonium salts include the chloride of 
trimethylaminoethyl-acrylamide or -methacrylamide, the bromide of 
trimethylaminopropyl-acrylamide or -methacrylamide, the methysulfate of 
trimethyl-aminobutyl-acrylamide or -methacrylamide, and the chloride of 
trimethylaminopropyl methacrylate. 
In addition to quaternary ammonium salts, unsaturated pyridinium, 
quinolinium, imidazolium and benzimidazolium salts may be used as the 
substance which generates cationic species. Examples of such onium salts 
include 1-methyl-2-vinylpyridinium bromide, 1-ethyl-2-vinyl-pyridinium 
chloride, 1-ethyl-2-vinylpyridinium methylsulfate, 
1-benzyl-4-vinylpyridinium chloride, 1-methyl-2-vinyl-quinolinium iodide, 
N-vinyl-N'-methylimidazolium bromide and 1-vinyl-3-methylbenzimidazolium 
bromide, (2-methacryloxy)-dimethylsulfonium chloride, 
methyldiallyl-sulfonium methylsulfate and trimethylvinylphosphonium 
bromide. 
The unsaturated nitrogen compound can be added to the reaction mixture 
during any stage of the polymerization of the non-ionic monomer. For 
example, the nitrogen compound can be added to the reaction mixture at the 
start of the polymerization process, continuously or discontinuously 
throughout the polymerization process, after at least about 30% of the 
non-ionic monomer has been converted to the synthetic polymer, or after 
polymerization is complete, when about 90 to 98% of the non-ionic monomer 
has been converted to the polymer. Thus, the reaction mixture can include 
both non-ionic monomers and polymerized non-ionic monomers. 
The substance which generates cationic species can be added to the reaction 
mixture before or simultaneously with the unsaturated nitrogen compound. 
In addition, the substance can be present in the reaction mixture, in the 
form of a cationic seed, at the start of the polymerization of the 
non-ionic monomer. The cationic seed is a polymer or copolymer previously 
prepared by aqueous emulsion polymerization, in a cationic medium, of the 
non-ionic monomer(s) in the presence of the desired amount of the 
substance which generates cationic charges. 
The amount of unsaturated nitrogen compound required is about 1 to 20%, 
preferably about 1 to 10% by weight of non-ionic monomer(s), expressed by 
weight of solids. 
The amount of substance which generates cationic species used in the 
claimed process depends on the hydrolysis level of both the unsaturated 
nitrogen compound and the substance which generates cationic species, and 
is determined by the molar ratio of the number of moles of the said 
substance initially in the reaction mixture plus the number of moles of 
the nitrogen compound to the number of moles of the non-ionic monomer 
initially in the reaction mixture. This ratio is generally between about 
0.1 and 15. For example, for a 90% hydrolysis level for the unsaturated 
nitrogen compound and a 0% hydrolysis level for the substance which 
generates cationic species, the preferred molar ratio is between about 1 
to 15, preferably between about 1 and 10. For a 10% hydrolysis level for 
the unsaturated nitrogen compound and a 0% hydrolysis level for the 
substance which generates cationic species, the molar ratio is preferably 
between about 0.1 and 1.5, most preferably between about 0.2 and 1. While 
for a 90% hydrolysis level for the unsaturated nitrogen compound and a 25% 
hydrolysis level for the substance which generates cationic species, the 
molar ratio is preferably between about 0.5 and 10, most preferably 
between about 1 and 5. 
The copolymerization of the nitrogen compound with the non-ionic monomer is 
carried out under conventional aqueous emulsion polymerization conditions, 
at a temperature between about 60.degree. C. and 90.degree. C., preferably 
between about 75.degree. C. and 85.degree. C., and at any pH, from about 3 
to about 12, most preferably from 5 to 9, in the presence of either a 
cationic or non-ionic initiator or emulsifying agent and, as 
aforementioned, in the presence of the substance which generates cationic 
charges. 
Those substances which generate cationic species may also be used as 
cationic initiators. 
Typical non-ionic initiators include (1) mineral or organic peroxides and 
hydroperoxides which are soluble in either water or organic solvents and 
which generate non-charged free radicals, such as hydrogen peroxide, 
benzoyl peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, 
tert-butyl perbenzoate, diisopropylbenzene peroxide, and methyl ethyl 
ketone peroxide, (2) redox systems obtained by combining the above 
peroxides or hydroperoxides with a reducing agent, such as ascorbic acid, 
sugars, polyvalent metal salts, sulfites, bisulfites, sulfoxalates, 
thiosulfates and bisulfites of sodium or calcium,, and the 
formaldehydesulfoxylate of sodium or zinc, and (3) azoaliphatic compounds 
having an azoacyclic group and an aliphatic carbon atom on each nitrogen 
atom, with at least one of the carbon atoms being tertiary, such as 
azobisisobutyronitrile, 2,2'-azo-bis(2,4-dimethylvaleronitrile), 
2,2'-azo-bis(2,4,4-trimethylvaleronitrile) and 
2,2'-azo-bis(2,4-dimethyl-4-methoxyvaleronitrile). 
Exemplary non-ionic emulsifiers include polyethoxylated fatty alcohols, 
polyethoxylated alkylphenols, and polyethoxylated fatty acids. 
Examples of cationic emulsifiers include decylammonium methylsulfate, 
N-ethyldodecylammonium bromide, cetylammonium chloride, cetylammonium 
bromide, stearylammonium bromide, cetyldimethylbenzylammonium bromide, 
N,N-dimethyldodecylammmonium chloride, N-methyltridecylammonium iodide, 
and the chlorides, bromides, sulfates, methylsulfates, or acetates of 
ethoxylated fatty amines. 
The amount of initiator used in the copolymerization of the nitrogen 
compound and the non-ionic monomer depends upon both the monomer used and 
the polymerization temperature, and is generally about 0.1 to 5%, 
preferably about 0.1 to 2%, by weight, based on the total weight of the 
monomer. However, if the initiator is the primary or one of the primary 
constituents of the substance which generates cationic species, a 
proportional amount of additional initiator should be used. 
The amount of emulsifier required to stabilize the copolymer particles can 
be as much as about 2% of the total weight of the monomer. 
The zeta potential of the claimed stable amphoteric aqueous dispersions of 
synthetic polymers can vary from about +80 mV to -60 mV measured at a pH 
of from about 2 to 12. 
The claimed amphoteric aqueous dispersions of synthetic polymers may be 
used as binders for coating paper, for finishing non-woven fabrics, or for 
coating metallic substrates. The substances listed as exemplary 
constituents of the aqueous dispersions of the claimed invention, and the 
following examples of the claimed process are illustrative and are not to 
be construed as limiting the invention delineated in the claims. 
EXAMPLE 1 
The polymerization process described below is carried out in an autoclave 
with 5 liter capacity and an anchor-type stirrer with a speed of 180 
revolutions per minute. 
866 g of dionized water, 7.5 g of cetyldimethylbenzyl-ammonium bromide, 15 
g of the chloride of trimethylamino-propylmethacrylamide, and 15 g of 
dimethylaminoethyl acrylate is charged cold into the autoclave. The 
temperature of the autoclave is raised to 75.degree. C. 
7.5 g of cationic initiator, 2,2'-azobis(2-amidinopropane) hydrochloride, 
and 50 g of deionized water are introduced simultaneously. 750 g of butyl 
acetate, 660 g of styrene, and 60 g of dimethyulaminoethyl acrylate are 
then added continuously at a constant rate over 5 hours. 
The autoclave is maintained at 75.degree. C. for 4 hours. After a total 
reaction time of 9 hours, the reaction is stopped by cooling. 
A stable crust-free latex with the following characteristics is obtained: 
pH: 8.1 
Amount of solids: 45.0% by weight 
Brookfield viscosity (50 rpm): 250 mPa/s 
Mean particle diameter: 0.11.mu. 
Number of grains: 240 ppm 
The number of grains is determined by sifting the grains through mesh 
screens 40 and 100.mu. wide, and adding the grain content from each sieve. 
The amphoteric nature of the produced dispersion is proven by measuring the 
zeta potential as a function of the pH. A MARK II microelectrophoresis 
apparatus, manufactured by RANK BROTHERS is used to measure the zeta 
potential, at 80 volts and at 25.degree. C., of a dispersion with a 0.05% 
polymer concentration. 
The following results are obtained: 
______________________________________ 
pH Zeta potential in mV 
______________________________________ 
4.5 +30 
8.3 0 (isoelectric point) 
9 -40 
______________________________________ 
EXAMPLE 2 
940 g of deionized water, 9.6 g of cetyldimethylbenzylammonium bromide, 9.6 
g of the chloride of trimethylaminopropylmethacrylamide, 24 g of 
dimethyulaminoethyl acrylate, and 72 g of vinyl acetate, are charged cold 
into an autoclave. 
The temperature of the autoclave is raised to 80.degree. C. 1,100 g of 
vinyl acetate, 9 g of 2,2'-azobis(2-amidinopropane) hydrochloride, 210 g 
of deionized water, and 3.6 g of sodium bicarbonate are introduced at a 
constant rate over 5 hours. 
The reaction is maintained for 4 hours. 
A stable crust-free latex with the following characteristics is obtained: 
pH: 4.2 
Amount of solids: 47.5% by weight 
Brookfield viscosity (50 rpm): 165 mPa/s 
Mean particle diameter: 0.1.mu. 
Number of grains: 165 ppm 
The zeta potential measurements are as follows: 
______________________________________ 
pH Zeta potential in mV 
______________________________________ 
4.5 +60 
8.5 0 
9 -30 
______________________________________ 
EXAMPLE 3 
866 g of deionized water, 7.5 g of cetyldimethylbenzylammonium bromide, 15 
g of the chloride of trimethylaminopropylmethacrylamide, and 15 g of 
dimethylaminoethyl methacrylate is charged cold into an autoclave. 
The temperature of the autoclave is raised to 75.degree. C. 7.5 g of 
2,2'-azobis(2-amidinopropane) hydrochloride and 50 g of deionized water 
are introduced. 1,140 g of styrene and 60 g of dimethyulaminoethyl 
methacrylate are added continuously at a constant rate over 5 hours. 
The reaction is thereafter maintained at 75.degree. C. for 4 hours. 
A stable crust-free latex with the following characteristics is obtained: 
pH: 75 
Amount of solids: 46.3% by weight 
Brookfield viscosity (50 rpm): 116 mPa/s 
Mean particle diameter: 0.1.mu. 
Number of grains: 115 ppm 
The zeta potential measurements are as follows: 
______________________________________ 
pH Zeta potential in mV 
______________________________________ 
4.5 +47 
8.3 0 
9 -52 
______________________________________ 
EXAMPLE 4 
866 g of deionized water, 7.5 g of cetyldimethylbenzylammonium bromide, 15 
g of the chloride of trimethylaminopropylmethacrylamide and 15 g of 
dimethylaminoethyl acrylate are charged cold into an autoclave. 
The temperature of the autoclave is raised to 75.degree. C. 7.5 g of 
2,2'-azobis(2-amidinopropane) hydrochloride and 50 g of deionized water 
are introduced simultaneously. 170 g of butyl acrylate, 750 g of ethyl 
acrylate, and 550 g of methyl methacrylate are added continuously at a 
constant rate over 5 hours. 
The reaction is maintained for 4 hours. 
A stable crust-free latex with the following characteristics is obtained: 
pH: 8.1 
Amount of solids: 42.5% by weight 
Brookfield viscosity (50 rpm): 126 mPa/s 
Mean particle diameter: 0.12.mu. 
Number of grains: 180 ppm 
The zeta potential measurements are as follows: 
______________________________________ 
pH Zeta potential in mV 
______________________________________ 
4.5 +28 
7.9 0 
8.5 -30 
______________________________________ 
EXAMPLE 5 
866 g of deionized water, 7.5 of cetyldimethylbenzylammonium bromide, and 
15 g of the chloride of trimethylaminopropylmethacrylamide are charged 
cold into an autoclave. 
The temperature of the autoclave is raised to 75.degree. C. 7.5 g of 
2,2'-azobis(2-amidinopropane) hydrochloride and 50 g of deionized water 
are introduced simultaneously. 795 g of butyl acrylate, 675 g of styrene, 
and 15 g of dimethylaminomethyl acrylate are then added continuously at a 
constant rate over 5 hours. 
The reaction was maintained at 75.degree. C. for 4 hours. 
A dispersion with the following characteristics is obtained: 
pH: 7.8 
Amount of solids: 46% by weight 
Brookfield viscosity (50 rpm): 90 mPa/s 
Mean particle diameter: 0.12.mu. 
Number of grains: 470 ppm 
The zeta potential measurements are as follows: 
______________________________________ 
pH Zeta potential in mV 
______________________________________ 
4.5 +42 
8.2 0 
8.8 -31 
______________________________________ 
EXAMPLE 6 
866 g of deionized water, 7.5 g of cetyldimethylbenzylammonium bromide, 15 
g of the chloride of trimethylaminopropylmethacrylamide, and 30 g 
dimethylaminoethyl methacrylate are charged cold into an autoclave. 
The temperature of the autoclave is raised to 75.degree. C. 7.5 g of 
2,2'-azobis(2-amidinopropane) hydrochloride and 50 g of deionized water 
are introduced simultaneously. 750 g of butyl acrylate, 675 g of styrene, 
and 30 g of dimethyulaminoethyl methacrylate are added continuously at a 
constant rate over 5 hours. 
The reaction is maintained at 75.degree. C. for 4 hours. 
A crust-free latex with the following characteristics is obtained: 
pH: 7.8 
Amount of solids: 41.9% by weight 
Brookfield viscosity (50 rpm): 96 mPa/s 
Mean particle diameter: 0.12.mu. 
Number of grains: 450 ppm 
The zeta potential measurements are as follows: 
______________________________________ 
pH Zeta potential in mV 
______________________________________ 
4.5 +45 
7.2 0 
9 -50 
______________________________________ 
EXAMPLE 7 
866 g of deionized water, 7.5 g of cetyldimethylbenzylammonium bromide, 15 
g of the chloride of trimethylaminopropylmethacrylamide, and 30 g of 
dimethylaminoethyl methacrylate are charged cold into an autoclave. 
The temperature of the autoclave is raised to 75.degree. C. 7.5 g of 
2,2'-azobis(2-amidinopropane) hydrochloride and 50 g of deionized water 
are introduced simultaneously. 750 g of butyl acrylate and 705 g of 
styrene are then added continuously at a constant rate over 5 hours. 
The reaction was maintained at 75.degree. C. for 4 hours. A stable 
crust-free latex with the following characteristics is obtained: 
pH: 7.8 
Amount of solids: 44.6% by weight 
Brookfield viscosity (50 rpm): 104 mPa/s 
Mean particle diameter: 0.12.mu. 
Number of grains: 410 ppm 
The zeta potential measurements are as follows: 
______________________________________ 
pH Zeta potential in mV 
______________________________________ 
4.5 +41 
7.9 0 
8.8 -29 
______________________________________ 
EXAMPLE 8 
866 g of deionized water, 7.5 g of cetyldimethylbenzylammonium bromide, 15 
g of the chloride of trimethylaminopropyl methacrylate, 15 g of 
dimethylaminoethyl acrylate, 75 g of styrene and 66 g of butyl acrylate 
are charged cold into an autoclave. 
The temperature of the autoclave is raised to 75.degree. C. 7.5 g of 
2,2'-azobis(2-amidinopropane) hydrochloride and 50 g of deionized water 
are introduced simultaneously. After about 30 minutes, when the exothermic 
reaction has ended and about 90% of the monomer has been converted to 
polymer, 594 g of butyl acrylate, 675 g of styrene, and 60 g of 
dimethylaminoethyl methacrylate, 15 g of 2,2'-azobis(amidinopropane) 
hydrochloride, and 420 g of deionized water are then added continuously at 
a constant rate over 5 hours. 
The reaction is thereafter maintained for 4 hours. 
A dispersion with the following characteristics is obtained: 
pH: 7.8 
Amount of solids: 45.4% by weight 
Brookfield viscosity (50 rpm): 305 mPa/s 
Mean particle diameter: 0.1.mu. 
Number of grains: 175 ppm 
The zeta potential measurements are as follows: 
______________________________________ 
pH Zeta potential in mV 
______________________________________ 
4.5 +49 
8.4 0 
9 -35 
______________________________________ 
EXAMPLE 9 
866 g of deionized water, 7.5 g of cetyldimethylbenzylammonium bromide, 15 
g of dimethyulaminoethyl methacrylate, 75 g of styrene, and 66 g of butyl 
acrylate are charged cold into an autoclave. 
The temperature of the autoclave is raised to 80.degree. C. 15 g of 
2,2'-azobis(2-amidinopropane) hydrochloride and 50 g of deionized water 
are introduced simultaneously. When the exothermic reaction has ended, 
after about 30 minutes, and the monomers are about 95% converted, 594 g of 
butyl acrylate, 675 g of styrene, 60 g of dimethylaminoethyl methacrylate, 
15 g of 2,2'-azobis(amidinopropane) hydrochloride, and 420 g of deionized 
water are added continuously at a constant rate over 5 hours. 
The reaction is maintained for 4 hours. 
A stable crust-free latex with the following characteristics is obtained: 
pH: 8.5 
Amount of solids: 40.1% by weight 
Brookfield viscosity (50 rpm): 78 mPa/s 
Mean particle diameter: 0.5.mu. 
Number of grains: 320 ppm 
The zeta potential measurements are as follows: 
______________________________________ 
pH Zeta potential in mV 
______________________________________ 
4.5 +33 
8.3 0 
8.8 -22 
______________________________________ 
EXAMPLE 10 
866 g of deionized water, 30 g of the chloride of 
trimethylaminopropylmethacryamide, 15 g of dimethylaminoethyl 
methacrylate, 75 g of styrene, and 66 g of butyl acrylate are charged cold 
into an autoclave. 
The temperature of the autoclave is raised to 75.degree. C. 7.5 g of 
2,2'-azobis(2-amidinopropane) hydrochloride and 50 g of deionized water 
are introduced simultaneously. When the exothermic reaction has ended, 
after about 30 minutes and a 90% conversion level, 594 g of butyl 
acrylate, 675 g of styrene, 60 g of dimethyulaminoethyl methacrylate, 15 g 
of 2,2'-azobis(amidinopropane) hydrochloride, and 420 g of deionized water 
are added continuously at a constant rate over 5 hours. 
The reaction is maintained for 4 hours. 
A stable crust-free latex with the following characteristics is obtained: 
pH: 8.2 
Amount of solids: 41.3% by weight 
Brookfield viscosity (50 rpm): 108 mPa/s 
Mean particle diameter: 0.12.mu. 
Number of grains: 468 ppm 
The zeta potential measurements are as follows: 
______________________________________ 
pH Zeta potential in mV 
______________________________________ 
4.5 +41 
8.4 0 
9 -29 
______________________________________ 
EXAMPLE 11 
866 g of deionized water, 7.5 g of cetyldimethylbenzylammonium bromide, 15 
g of the chloride of trimethylaminopropylmethacrylamide, and 45 g of 
dimethylaminoethyl acrylate are charged cold into an autoclave. 
The temperature of the autoclave is raised to 75.degree. C. 7.5 g of 
2,2'-azobis(2-amidinopropane) hydrochloride and 50 g of deionized water 
are introduced simultaneously. 750 g of butyl acrylate, 615 g of styrene, 
and 75 g of dimethyulaminoethyl acrylate are then added continuously at a 
constant rate over 5 hours. 
The reaction is maintained for 4 hours at 75.degree. C. 
A crust-free latex with the following characteristics is obtained: 
pH: 7.6 
Amount of solids: 42% by weight 
Brookfield viscosity (50 rpm): 82 mPa/s 
Mean particle diameter: 0.1.mu. 
Number of grains: 298 ppm 
The zeta potential measurements are as follows: 
______________________________________ 
pH Zeta potential in mV 
______________________________________ 
4.5 +42 
8.9 0 
9.5 -38 
______________________________________ 
EXAMPLE 12 
The procedure of Example 5 is repeated with the 15 g of dimethylaminomethyl 
acrylate added over 2 hours, instead of over 5 hours, with the 15 g of 
dimethylaminoethyl acrylate thus added during hour 4 to hour 6 of the 
reaction and after the reaction has reached about a 92% conversion level. 
A dispersion with the following characteristics is obtained: 
pH: 8 
Amount of solids: 45.2% by weight 
Brookfield viscosity (50 rpm): 120 mPa/s 
Mean particle diameter: 0.12.mu. 
Number of grains: 412 ppm 
The zeta potential measurements were as follows: 
______________________________________ 
pH Zeta potential in mV 
______________________________________ 
4.5 +38 
8 0 
8.5 -20 
______________________________________ 
EXAMPLE 13 
333 g of the latex produced in Example 1, which is 150 g of solids, i.e. 
about 10% by weight of the latex, 866 g of deionized water, and 15 g of 
the chloride of triemethylaminopropylmethacrylamide are charged cold into 
an autoclave. 
The temperature of the autoclave is raised to 75.degree. C. 7.5 g of 
cationic initiator, 2,2'-azobis(2-amidinopropane) hydrochloride and 50 g 
of deionized water are introduced simultaneously. 750 g of butyl acrylate, 
675 g of styrene, and 60 g of dimethylaminoethyl acrylate are then added 
continuously at a constant rate over 5 hours. 
The reaction is maintained at 75.degree. C. for 4 hours. After a total 
reaction time of 9 hours, the reaction is stopped by cooling. 
A stable crust-free latex with the following characteristics is obtained: 
pH: 8.1 
Amount of solids: 42.1% 
Brookfield viscosity (50 rpm): 112 mPa/s 
Mean particle diameter: 0.22.mu. 
Number of grains: 378 ppm 
The zeta potential measurements are as follows: 
______________________________________ 
pH Zeta potential in mV 
______________________________________ 
4.5 +49 
7.9 0 
8.5 -36 
______________________________________ 
EXAMPLE 4 
The process of Example 4 is repeated, but the 15 g of the chloride of 
trimethylaminopropylmethacrylamide is replaced by 15 g of 
1-methyl-2-vinylpyridinium bromide. 
A latex with the following characteristics is obtained: 
pH: 7.6 
Amount of solids: 46.2% 
Brookfield viscosity (50 rpm): 188 mPa/s 
Mean particle diameter: 0.12.mu. 
Number of grains: 425 ppm 
The zeta potential measurements are as follows: 
______________________________________ 
pH Zeta potential in mV 
______________________________________ 
4.5 +39 
8.1 0 
9 -22 
______________________________________ 
EXAMPLE 15 
The process of Example 6 is repeated, but the 15 g of the chloride of 
trimethylaminopropylmethacrylamide are replaced by 15 g of the chloride of 
trimethylaminoethylacrylamide. 
A latex with the following characteristics is obtained: 
pH: 7.9 
Amount of solids: 45.7% 
Brookfield viscosity: 165 mPa/s 
Means particle diameter: 0.12.mu. 
Number of grains: 365 ppm 
The zeta potential measurements are as follows: 
______________________________________ 
pH Zeta potential in mV 
______________________________________ 
4.5 +42 
8.9 0 
9 -28 
______________________________________