Process for producing a stabilized latex emulsion adhesive

An improved process for producing stabilized core-shell latex emulsion adhesives is disclosed. In a process which comprises preparing a hydrophilic polymer and thereafter contacting the hydrophilic polymer with a hydrophobic monomer for producing an inverted core-shell latex emulsion, the improvement comprises the additional step of adjusting the pH of the inverted core-shell latex emulsion for dissolving the hydrophilic polymer, thereby to produce a stabilized latex emulsion adhesive.

BACKGROUND OF THE INVENTION 
This invention relates to stable, aqueous latexes and to methods for their 
preparation. 
Aqueous dispersions of polymers, which are referred to as "latexes" in the 
art, are generally known to be useful, both alone and in a variety of 
formulations, as, for example, coatings and impregnants. A wide variety of 
latexes of various homopolymeric and copolymeric compositions (such as 
styrene-butadiene copolymers, acrylic homopolymers and copolymers, 
vinylidene chloride homopolymers and copolymers, etc.) have been developed 
having specific chemical and/or mechanical properties for particular end 
use applications. 
In particular, aqueous interpolymer latexes resulting from the 
emulsion-polymerization of: certain monovinyl aromatic monomers such as 
styrene; certain diolefins such as butadiene; and certain 
monoethylenically-unsaturated carboxylic acids such as acrylic acid, are 
known to be particularly useful as film-forming binders for pigments in 
various paper-coating applications. See, for example, U.S. Pat. No. 
3,399,080 to Vitkuske and U.S. Pat. No. 3,404,116 to Pueschner et al. Such 
emulsion polymerization reactions may also optionally employ conventional 
seeding procedures to obtain optimum control of polymerization and, 
therefore, maximum product uniformity (e.g., narrow particle size 
distribution). 
U.S. Pat. No. 4,151,143 to Blank et al., moreover, discloses a so-called 
"surfactant-free" polymer emulsion coating composition and a method for 
preparing the same. Blank et al. point out that one problem associated 
with emulsion polymerization-produced polymers that are employed for 
coatings is the presence of certain surfactants. That is, certain 
surfactants, while employed to stabilize emulsions, tend to adversely 
affect the water-resistance and/or corrosion-resistance of the resulting 
film as well as the adhesion of the coating especially to metal surfaces. 
The Blank et al. emulsion polymers, furthermore, are prepared in a 
so-called "two-stage" process. The process includes a first stage and a 
second stage. In the first stage, a conventional carboxyl group-containing 
polymer is prepared either by a conventional solution-polymerization 
technique or by a bulk-polymerization technique, and thereafter is 
water-dispersed or solubilized by partial or full neutralization with an 
organic amine or base and application of high shear agitation. In the 
second stage, a mixture of polymerizable monomers and polymerization 
catalyst is added to the first-stage emulsion at an elevated temperature 
to effect polymerization of the second-stage monomers, resulting in the 
formation of an emulsion coating composition. Such a coating composition 
is thus said to be "surfactant-free". 
U.S. Pat. No. 4,179,417 to Sunada et al. discloses a composition for 
water-based paints, such composition containing a water-soluble resin and 
a water-dispersible polymer. The water-soluble resin contains 50-99.5 
percent by weight of either an alpha, beta monoethylenically-unsaturated 
acid alkyl ester or an alkenyl benzene; 0.5-20 percent by weight of an 
alpha, beta monoethylenically-unsaturated acid; and 0-30 percent by weight 
of a hydroxyalkyl ester of an alpha, beta monoethylenically-unsaturated 
acid. These monomers are polymerized in the presence of at least one 
unsaturated compound selected from the group consisting of an alkyd resin 
containing a polymerizable unsaturated group, an epoxy ester containing a 
polymerizable unsaturated group, a drying oil, a fatty acid of a drying 
oil, and a diene polymer. The resulting polymers are water-solubilized by 
the addition of ammonia or an amine. The water-dispersible polymer 
contains not only hydroxy and/or carboxyl functional groups but also an 
alpha, beta monoethylenically-unsaturated acid monomer and/or a hydroxy 
alkyl ester of such a monomer as well as certain other 
ethylenically-unsaturated monomers. The compositions disclosed in U.S. 
Pat. No. 4,179,417 are employed in water-based paints and can optionally 
contain a cross-linking agent. 
Canadian Pat. No. 814,528 to Kaminski discloses low molecular weight 
alkali-soluble resin, resin solutions and methods for their preparation 
and purification. The disclosed resins are said to be especially useful as 
emulsifiers, leveling agents, and film-formers. Kaminski discloses that 
the number-average molecular weight of such a resin ranges from 700-5000 
and that such a resin can have an acid number which ranges between 
140-300. The resins are further disclosed as being useful as emulsifiers 
in the preparation of emulsion polymers, resulting in emulsion polymers 
that are said to be stable and substantially free from coagulum. In 
connection with such a use, i.e. use as an emulsifier in an 
emulsion-polymerization reaction, the resins are said to require a 
number-average molecular weight of between 1,000 and 2,000 and preferably 
between 1,000 and 1,500. Resins having a number-average molecular weight 
greater than 2,000 are said to lead to unstable and coagulated emulsion 
polymers when used as the emulsifier in a conventional 
emulsion-polymerization reaction. 
Two-stage latex polymers are known to exist in many morphological forms, 
which are determined by many factors including the relative 
hydrophilicity, miscibility and molecular weights of the first-stage and 
second-stage polymers. 
So-called "core-shell" latexes are formed when such a second-stage polymer 
forms a "shell" (or coating) around a discrete "core" (or domain) of the 
first-stage polymer. Examples of such core-shell latexes are disclosed in 
U.S. Pat. No. 4,515,914 to Tsurumi et al., where an exemplary composition 
containing a first-stage styrene/butadiene polymeric core is encapsulated 
by a second-stage monovinyl polymeric shell. 
So-called "inverted core-shell" latexes are also known. Lee and Ishikawa, 
in an article entitled "The Formation of `Inverted`, Core-Shell Latexes," 
and appearing in J. Poly. Sci., 21, 147-154 (1983), shows that such 
"inverted" latexes are those where the second-stage polymer becomes the 
"core" domain and is encapsulated by the first-stage polymeric shell. 
These inverted latex compositions can be formed when the first-stage 
polymer is more hydrophilic than the second-stage polymer. Lee and 
Ishikawa studied the formation of the "inverted" core-shell morphology 
using two polymer pairs: a soft polymer pair [ethyl acrylate/methacrylic 
acid (EA/MAA) (90/10)]/[styrene/butadiene (S/B)(60/40)] and a hard polymer 
pair [EA/S/MAA (50/40/10)]/[S (100)]. The ratio of monomers in each 
polymer is in parts-by-weight. Soft polymers have a relatively low 
glass-transition temperature (Tg), generally below about 20 degrees 
Celsius, while hard polymers have a relatively high Tg, generally above 
about 20.degree. C. It was found, in the case of the soft polymer pair 
systems, that the formation of inverted core-shell morphology was equally 
complete regardless of the molecular weight of the hydrophilic polymer 
molecules, whereas in the case of the hard polymer pair systems it was 
found that the efficiency of inversion depended upon the molecular weights 
of the hydrophilic and hydrophobic polymers. The Lee and Ishikawa study 
further suggests that the formation of inverted core-shell latexes depends 
not only on the hydrophilicity, the interfacial tension, and the molecular 
weight of the hydrophilic polymer molecules, but also on the extent of 
phase separation between the two polymers. Lee and Ishikawa also point out 
a particular "alkali-swellability" aspect of the first-stage polymer, in 
connection with those inverted emulsion systems which they investigate. 
Muroi et al., in an article titled "Morphology of Core-Shell Latex 
Particles," and appearing in J. Poly. Sci., 22, 1365-1372 (1984), 
evaluated certain latex particles which are formed when either an ethyl 
acrylate-methacrylic acid (EA-MAA) containing mixture of a methyl 
acrylate-methacrylic acid (MA-MAA) containing mixture was polymerized in 
the presence of either poly methyl acrylate/methacrylic acid seeds or poly 
ethyl acrylate/methacrylic acid seeds. These investigators discovered (I) 
that the shell was composed of the more hydrophilic poly (MA/MAA) 
molecules which were relatively high in MAA content and (2) that the core 
was composed of both poly (MA/MAA) and poly (EA/MAA) molecules, with the 
thus-investigated copolymeric particles being relatively uniform from 
surface to center with respect to distribution of all other components 
(i.e., except for MAA). The monomer content of MAA, in particular, was 
found to increase in the direction of the shell surface. 
More particularly, Muroi et al. studied five compositions, including one 
where the first-stage feed was MA/MAA (90/10) and the second-stage feed 
was EA/MAA (90/10). These investigators discovered that as the pH of the 
resulting latex was increased, as a result of the addition of NaOH, the 
optical density decreased, indicating complete dissolution of all the 
latex particles. 
In view of the above, it is desirable to provide a stable latex emulsion 
that is capable of employing a relatively broad spectrum of hard and soft 
monomers wherein such monomers possess "acidic" as well as "basic" 
functionality. 
SUMMARY OF THE INVENTION 
The present invention is directed to a stabilized latex emulsion and the 
process for preparing it. The process comprises: 
(a) preparing a hydrophilic, low molecular weight first-stage polymer by 
emulsion polymerization; 
(b) conducting a second emulsion polymerization to produce a hydrophobic 
second-stage polymer under conditions sufficient to cause the second-stage 
polymer to partition into the first-stage polymer thus producing an 
inverted core-shell latex; then 
(c) adjusting the pH of the resulting inverted core-shell emulsion to 
dissolve the first-stage polymer, thereby creating a continuous aqueous 
phase consisting of the first-stage polymer and a discontinuous phase 
containing discrete stabilized particles of the second-stage polymer. 
The latexes of this invention exhibit excellent mechanical properties as a 
result of the stabilization of the second-stage polymer. Many latexes of 
this invention exhibit superior coating properties for those applications 
known in the art. Such applications include uses in floor polish, 
varnishes, including water-borne graphic arts varnishes, paints, inks, 
adhesives, and the like.

DETAILED DESCRIPTION OF THE INVENTION 
The polymer particles of this invention are broadly characterized as latex 
particles comprising a hydrophilic first-stage polymer dissolved in a 
continuous aqueous phase containing discrete domains of a hydrophobic 
second-stage polymer. As employed herein the term "hydrophilic" means that 
the polymer is capable of being dissolved in an aqueous medium upon 
adjustment of the pH. First-stage polymers containing acid-functional 
groups (i.e., possessing "acidic" functionality) will be solubilized upon 
addition of alkali; first-stage polymers containing basic functional 
groups (i.e., possessing "basic" functionality) will be solubilized upon 
addition of acid. 
The term "hydrophobic" as used herein includes a polymer which will not be 
dissolved in any aqueous medium by adjusting the pH. 
For purposes of this invention, the term "inverse core-shell latex" means a 
latex formed in a two-stage polymerization process wherein the 
second-stage polymer tends to form a "core" domain in the first-stage 
polymer. The first-stage polymer may encapsulate the second-stage polymer, 
or may form a "shell" around the second-stage polymer "core", or may 
incorporate the second-stage polymer into its swollen matrix. It is also 
possible to engraft a portion of the second-stage polymer to the 
first-stage polymer to further stabilize the first-stage polymer. 
"Emulsion polymerization" as the term is employed herein is a process that 
requires a polymerizable monomer or polymerizable co-monomers, an 
initiator, and water as the continuous phase. This invention may also 
optionally utilize such commonly-used emulsion-polymerization ingredients 
as chain-transfer agents to regulate the molecular weight of the resulting 
first-stage polymer and/or second-stage polymer, as well as conventional 
free-radical polymerization catalysts and/or conventional cross-linking 
agents, if desired. 
The first step in the emulsion polymerization process of this invention is 
selecting the monomers which will produce the hydrophilic first-stage 
polymer. The monomers should be selected so that there is at least one 
monomer from each of two monomer groups, namely (i) specified monomers 
that are at least partially water-insoluble and (ii) specified "acidic" or 
"basic" functional group-containing monomers. 
As employed herein, the term "water insoluble monomers" is intended to 
include those monomers that form polymers which, upon pH adjustment, do 
not become appreciably water-soluble. 
As employed herein, the term "functional group-containing monomers" 
includes those monomers that form polymers whose solubility 
characteristics become appreciably changed upon pH adjustment. 
Typical monomers that are at least partially water-insoluble, for purposes 
of the present invention, are certain open-chain conjugated dienes as well 
as certain vinyl monomers such as monovinyl aromatic monomers. 
More particularly, with respect to the hydrophilic first-stage polymer of 
the present invention, a suitable monomer that is at least partially 
water-insoluble is selected from the group consisting of styrene, methyl 
styrene, alpha-methyl styrene, ethyl styrene, isopropyl styrene, tertiary 
butyl styrene, ethyl methacrylate, methyl methacrylate, butyl acrylate, 
butyl methacrylate, 2-ethyl hexylacrylate, ethyl acrylate, vinyl acetate, 
methyl acrylate, open-chain conjugated dienes, 2-hydroxyethyl 
methacrylate, 2-hydroxyethyl acrylate, methylol acrylamide, glycidyl 
acrylate, glycidyl methacrylate, and combinations thereof. Preferably, the 
hydrophilic first-stage polymer is produced from a monoalkenyl aromatic 
monomer such as methyl styrene, alpha-methyl styrene, tertiary-butyl 
styrene or, most preferably, styrene. 
With respect to the hydrophobic second-stage polymer of the present 
invention, a suitable monomer that is at least partially water-insoluble 
is selected from the group consisting of styrene, methyl styrene, 
alpha-methyl styrene, ethyl styrene, isopropyl styrene, tertiary butyl 
styrene, ethyl methacrylate, methyl methacrylate, butyl acrylate, butyl 
methacrylate, 2-ethyl hexylacrylate, ethyl acrylate, vinyl acetate, methyl 
acrylate, open-chain conjugated dienes, 2-hydroxyethyl methacrylate, 
2-hydroxyethyl acrylate, methylol acrylamide, glycidyl acrylate, glycidyl 
methacrylate, an aromatic or an acrylate or a methacrylate having a 
functionality of at least 2, and combinations thereof. 
One suitable aromatic monomer having a functionality of at least two, for 
example, is divinyl benzene. Suitable acrylate monomers having a 
functionality of at least two or greater, for example, include: 1,3-butane 
diol diacrylate; 1,4-butane diol diacrylate; ethylene glycol diacrylate; 
diethylene glycol diacrylate; triethylene glycol diacrylate; tetraethylene 
glycol diacrylate; 1,6-hexane diol diacrylate; pentaerythritol 
tetraacrylate; and trimethylol propane triacrylate. Suitable methacrylate 
monomers having a functionality of at least 2, for example, include: 
1,3-butane diol dimethacrylate; 1,4-butane diol dimethacrylate; ethylene 
glycol dimethacrylate; diethylene glycol dimethacrylate; triethylene 
glycol dimethacrylate; tetraethylene glycol dimethacrylate; 1,6-hexane 
diol dimethacrylate; pentaerythritol tetramethacrylate; and trimethylol 
propane trimethacrylate. 
As employed herein, the term "monovinyl aromatic monomer" includes those 
monomers wherein a radical of the formula 
##STR1## 
is attached directly to an aromatic nucleus containing from 6 to 10 carbon 
atoms, wherein R is hydrogen or a lower alkyl such as an alkyl having from 
1 to 4 carbon atoms, including those monomers wherein the aromatic nucleus 
portion is substituted with alkyl or halogen substituents. Suitable 
monovinyl aromatic monomers, for purposes of the present invention, are 
styrene; alpha-methyl styrene; ortho-, meta- and para-methyl styrene; 
ortho-, meta- and para-ethyl styrene; O-methyl-para-isopropyl styrene; 
para-chloro styrene; para-bromo styrene; ortho, para-dichloro styrene; 
ortho, para-dibromo styrene; vinyl naphthalene; diverse 
vinyl(alkyl-naphthalenes) and vinyl(halonaphthalenes), and co-monomeric 
mixtures thereof. 
The term "open-chain conjugated diene" is meant to include, for example, 
1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 
pentadiene, 2-neopentyl-1,3-butadiene and other hydrogen analogs of 
1,3-butadiene and, in addition, the substituted 1,3-butadienes, such as 
2-chloro-1,3-butadiene, 2-cyano-1,3-butadiene, the substituted 
straight-chain conjugated pentadienes, the straight-chain and 
branched-chain conjugated hexadienes, other straight and branched-chain 
conjugated dienes typically having from 4 to about 9 carbon atoms, and 
co-monomeric mixtures thereof. 
The functional group-containing monomers of the present invention can have 
basic or acidic functionalities such as amino or carboxy functionality. 
Typical functional group-containing monomers include "acidic" 
group-containing monomers such as acrylic acid, methacrylic acid, other 
unsaturated acid monomers, and combinations of these, and "basic" 
group-containing monomers such as vinyl pyridines, amino acrylates and 
methacrylates, and combinations of these. Typical amines include the vinyl 
pyridines, dimethyl aminoethyl methacrylate and tert-butyl amino ethyl 
methacrylate. 
The acrylic monomers employed in the process of the present invention 
include acrylic acid or methacrylic acid, either alone or admixed with at 
least one other unsaturated monomer such as an ester of acrylic or 
methacrylic acid, 2-hydroxyethyl methacrylate, methacrylonitrile, 
acrylonitrile, and the like, and combinations of these. 
Other unsaturated acid monomers can also be substituted in minor part for 
the preferred acrylic acids of the present invention. Such unsaturated 
acid monomers include maleic acid, crotonic acid, fumaric acid, itaconic 
acid, vinyl benzoic acid, isopropenyl benzoic acid, and combinations 
thereof. 
The glass-transition temperature (Tg) of the first-stage polymer is an 
important factor in achieving the desired film forming properties of a 
particular stabilized latex product. Therefore, monomers are selected such 
that the first-stage polymer will exhibit a Tg suitable for a particular 
end-use application. 
The first-stage monomers are, accordingly, selected so that a hydrophilic 
first-stage polymer will be produced. Additionally, the monomers are 
selected with a view toward the ultimate use of the latex film that is to 
be produced as well as the chemical resistance required of the 
thus-produced latex film. If the resulting emulsion is to be crosslinked, 
for example, then crosslinkable monomers should be used to form the 
first-stage polymer. 
Preferred monomer formulations for the first-stage polymer include ethyl 
acrylate (EA) and methacrylic acid (MAA) and, particularly, the 
combination 80 EA/20 MAA. Styrene (S) and acrylic acid (AA) form another 
preferred composition, particularly, the combination 60 S/40 AA. A third 
preferred monomer composition, for purposes of preparing the hydrophilic 
first-stage polymer, is methyl methacrylate (MMA), butyl acrylate (BA) and 
methacrylic acid (MAA), especially 58 MMA/30 BA/12 MAA. 
Sufficient functional group-containing monomer is present to ensure that 
the first-stage polymer will dissolve upon adjustment of the pH. For this 
and other purposes, the ratio of water-insoluble monomer to 
functional-group monomer is from 20:1 to 1:3. A more preferred ratio is 
from 10:1 to 1:1. The most preferred embodiment is where the 
water-insoluble monomer to functional-group monomer ratio varies from 7:1 
to 3:2. 
A chain-transfer agent is preferably added to the first stage monomers 
during emulsion polymerization to regulate the molecular weight of the 
first-stage polymer. (As those skilled in the art well know, the addition 
of a chain-transfer agent will enable one to regulate not only the 
number-average molecular weight but also the weight-average molecular 
weight of the first-stage polymer.) The number-average molecular weight 
should generally not exceed about 20,000, otherwise the first-stage 
polymer will usually cause the system to become exceedingly viscous upon 
pH adjustment. However, employing higher molecular weight might be useful 
for some compositions, especially those where high viscosity is desirable. 
As employed herein the phrase "molecular weight" refers to the 
number-average (Mn) molecular weight, unless indicated otherwise. 
The first-stage polymer must be capable of dissolving upon proper 
adjustment of the pH. For this and other purposes, such as viscosity 
considerations, the preferred molecular weight for the first-stage polymer 
is from about 3,000 to 15,000. The most preferred molecular weight is from 
about 5,000 to 10,000. 
Selection of appropriate chain-transfer agents for molecular weight control 
is important for obtaining homogeneous, low molecular weight polymers. 
Chain-transfer agents must be efficient, must exhibit high transfer 
activity, must produce controllable molecular weight distribution, and 
must not adversely affect the polymerization rates. Conventional 
chain-transfer agents which meet these standards, such as mercapto 
carboxylic acids having 2 to 8 carbon atoms, and their esters, may be 
employed. Examples of suitable chain-transfer agents, still more 
particularly, are mercaptoacetic acid, 2-mercaptopropionic acid, 
3-mercaptopropionic acid, 2-mercaptobenzoic acid, mercaptosuccinic acid, 
mercaptoisophthalic acid and alkyl esters thereof, and combinations 
thereof. It may also be desirable to employ a mercapto monocarboxylic acid 
and/or a mercapto dicarboxylic acid containing 2 to 6 carbon atoms such as 
mercaptopropionic acid and the alkyl ester thereof, or the butyl or 
isooctyl ester of mercaptopropionic acid. 
Other organic-type chain-transfer agents, including halogenated 
hydrocarbons such as bromoform, carbon tetrachloride and 
bromotrichloromethane, may also be desirable. 
For example, when producing stabilized latex emulsion adhesives, the 
chain-transfer agent is preferably selected from the group consisting of 
bromotrichloromethane, butyl mercaptopropionate, dodecyl mercaptan, 
mercaptoethanol, octyl mercaptan, and combinations of these. 
In general, there is a reduction in polymerization rate and an increase in 
steady-state monomer concentration with increasing addition levels of 
chain-transfer agent. Generally, no greater than about 6 mole percent (mol 
%) of chain-transfer agent is employed, based on total molar weight of the 
monomer charged. On the other hand, as the addition level of 
chain-transfer agent is reduced, both the polydispersity index or ratio as 
well as the molecular weight of the polymer tend to increase, because a 
lesser amount of chain-transfer agent results in a reduced level of 
chain-transfer activity. (For the meaning of "polydispersity ratio", 
please refer to U.S. Pat. No. 4,529,787 to Schmidt et al.) Accordingly, no 
less than about 0.5 mol % chain-transfer agent is normally employed. If it 
is desirable to make polymers of greater molecular weight and/or 
polydispersity values, then the amount of chain-transfer agent employed 
can be reduced to below 0.5 mol %, say, to at least about 0.3 mol %. 
Depending upon the end-use, however, it may be desirable to use from about 
1-3 mol % of a chain-transfer agent. 
The chain-transfer agent is normally added to the reaction mix 
incrementally, along with the monomers of the first stage. A portion of 
the chain-transfer agent may be added to a functional group-containing 
monomer precharge, usually in the same relative proportion as the 
functional group monomer. For most purposes, the precharge preferably 
contains about 10 weight percent (wt.-%) of the entire charge of 
chain-transfer agent. The choice of type and amount of chain-transfer 
agents, and their effects, are well known to those skilled in the art. 
Initiation is a factor to consider in connection with the emulsion 
polymerization process; and choice of suitable initiator is important for 
the preparation of homogeneous products. For example, to enhance initiator 
efficiency, to provide desired polymerization rates, and to provide 
product of a particular fine-particle size, it may be preferable to 
gradually add initiator to a particular reaction mixture. Precharging 
initiator prior to the onset of polymerization, or rapidly adding 
initiator along with the monomers, may yield premature destruction of 
initiator from the high concentrations of radical thereby produced. 
Employing high polymerization temperatures may also induce early 
consumption of initiator. For the above and other purposes, 
low-temperature initiators are preferred. Best results are attained with 
persulfate initiators such as sodium persulfate or potassium persulfate or 
barium persulfate and, especially, with ammonium persulfate (APS). 
Mixtures of such initiators may also be employed. 
In general, from about 0.25 to 2 wt.-% of initiator, based on the total 
weight of all initiator and monomer charged, is employed. The particular 
identity and quantity of initiator selected will of course depend, in 
part, upon the desired polymerization rate, the co-monomer addition rate, 
the polymerization reaction temperature, and the like. 
If desired, a post-addition of initiator may be employed to drive the 
reaction to completion. The choice of type of initiator, and amount of 
initiator, as well as the effect will be apparent to those skilled in the 
art. 
An emulsifier, typically an anionic emulsion-polymerization surfactant such 
as sodium lauryl sulfate, can be utilized to promote desired emulsion 
polymerization and to stabilize a particular polymerization reaction. 
Other emulsifiers, such as alkali metal sulfates, sulfonates and/or 
sulfosuccinic esters and so-called "non-ionics", as well as combinations 
of these, can also be utilized. 
The selection of the monomers that make up the hydrophobic second-stage 
polymer is important. These monomers can be selected from the group of 
monomers set forth hereinabove (described in connection with the 
first-stage polymer); however, such monomers as well as their relative 
ratios are selected so that the resulting polymer will not be water 
soluble upon pH adjustment. Further, the resulting second-stage polymer 
must be capable of partitioning into the first-stage polymer, so as to 
form "domains" on or within the first-stage polymer. Accordingly, the 
second-stage polymer must be relatively incompatible with the first-stage 
polymer. 
The molecular weight of the second-stage polymers may also be modified or 
regulated by use of the chain-transfer agents discussed hereinabove. One 
function of the second-stage polymer may be to enhance film strength. For 
that purpose the molecular weight should be significantly higher than that 
employed for the first-stage polymer. Generally, molecular weights of 
15,000 to 200,000 are acceptable for the second-stage polymers of this 
invention. Higher molecular weights, if desired, can be obtained by 
methods known in the art, such as cross-linking. Preferred molecular 
weights are from 20,000 to 150,000. The most preferred molecular weight 
range for the second stage polymer is 25,000 to 100,000. 
In general, the weight ratio of first-stage polymer to second-stage monomer 
can range from about 1:20 to 1:1. Preferably, the ratio is from about 1:15 
to 1:2. In the most preferred embodiments, the ratio of first-stage 
polymer to second stage monomer is from about 1:0 to 1:3. 
In general, the process of the present invention is conducted at the 
temperature range for conventional emulsion polymerization, known to those 
skilled in the art. For most purposes, the reaction temperatures are 
maintained at about 70.degree. C. to about 90.degree. C. and preferably at 
about 80.degree. C. Lower temperatures, if desired, may be utilized using 
re-dox polymerization techniques, as is well known to those skilled in the 
art. It is generally preferred that the second-stage monomers be 
polymerized at a temperature above the glass-transition temperature (Tg) 
for the first-stage polymer. This will soften the first-stage polymer, 
will permit the second-stage polymer to form domains therein, and will 
permit the first-stage polymer to flow more readily, the result being that 
the first-stage polymer will better encapsulate the second-stage polymer 
product. 
To assist in stabilizing the polymer product, and to ensure completion of 
the reaction, it may be desirable to maintain the reaction mixture at the 
desired reaction temperature for a period of about 1 hour, or more, after 
the final additions of co-monomers, initiator, and chain-transfer agent. 
The second-stage emulsion polymer is formed from monomers which polymerize 
so as to form a "hydrophobic" polymer, as defined hereinabove. Monomers 
similar to those employed for the first stage can be used in the second 
stage, except that lesser amounts of functional group-containing polymers 
are employed to prevent solubilization upon dissolution of the first-stage 
polymers. In this instance, it: is preferred that the second-stage polymer 
contain no more than about 10 mol % of functional monomer. 
Copolymers of monomers such as monovinyl aromatic monomers, 
monoethylenically-unsaturated carboxylic acids and esters thereof, 
conjugated dienes, acrylonitrile, vinyl acetate, vinyl dichloride, and the 
like, and combinations of these, can thus be employed as second-stage 
monomers. Because of considerations such as desired polymer properties, 
availability and compatability with the polymer formed (by polymerizing 
the aforementioned monomer charge), it has been found that copolymers of 
styrene and acrylate esters and/or methacrylate esters--such as methyl 
methacrylate, butyl methacrylate, 2-ethylhexyl acrylate, and the like, and 
combinations of these--are preferred. 
In order to promote desired core-shell inversion, it may be desirable to 
adjust the pH of the first-stage polymer reaction mixture to swell and 
plasticize the first-stage polymer, thereby to promote second-stage 
polymer domain formation in the first-stage polymer. A plasticizer or a 
coalescing agent may similarly promote domain formation. 
The reaction conditions for second-stage emulsion polymerization reaction 
are similar to those of the first-stage reaction, at least with regard to 
initiator, chain-transfer agent, emulsifier, and reaction parameters. 
After desired polymerization has occurred, the solids content of the 
resulting aqueous polymer latex can be adjusted to the level desired by 
adding water thereto or by distilling water therefrom. Generally, a 
desired level of polymeric solids content is from about 20 to about 65 
wt.-%, and preferably from about 30 to about 55 wt.-%, on a total weight 
basis. 
In selecting reaction conditions for the second-stage polymerization 
reaction, it should be understood that sufficient initiator may still be 
present from the first-stage reaction to conduct the second-stage 
reaction. Addition of more chain-transfer agent may, however, be necessary 
to bring about the desired second-stage polymerization reaction, depending 
upon the desired molecular weight of the second-stage polymer. On the 
other hand, use of additional emulsifier is often unnecessary in the 
second-stage polymerization reaction. 
Those skilled in the art will therefore appreciate that reaction parameters 
and adjuvants can be modified, as needed, to provide optimum second-stage 
reaction conditions. 
The emulsion-polymerization process can, moreover, be conducted as a batch 
process, or as a semi-continuous process, as desired. 
Further, the addition rate of first-stage monomer may be important, 
particularly if there is difficulty in obtaining uniformity of 
composition, for example, due to the tendency of certain monomers to 
partition to different phases. A particular example is a first stage of 
styrene and acrylic acid wherein monomer-starved conditions are necessary. 
In such a case, a one-hour addition may be unsatisfactory, whereas a 
three-hour addition might be preferable. Usually, an addition rate of 
about 0.5 to about 4 hours is sufficient for most semi-continuous 
polymerization reactions, dependent, of course, on the type and amount of 
initiator, the monomers employed, and the polymerization rate, as is well 
known to those skilled in the art. 
The rate of addition of the second-stage monomer may also be important. 
Providing a high rate of second-stage monomer addition may make the 
first-stage polymer more soluble. This can affect morphology and grafting. 
Similar rates of addition, as compared to first-stage addition, are 
normally employed but this also depends on polymerization rates. 
Once the inverted core-shell latex has been formed, the pH of the emulsion 
is adjusted to dissolve the first-stage polymer. If acidic functional 
group monomers are selected for the first-stage polymer, addition of a 
suitable base is appropriate. If basic functional group monomers are 
selected for the first-stage polymer, addition of an acid is appropriate. 
Suitable bases which can be used to adjust the pH include organic and 
inorganic bases. Examples of suitable organic bases include amines, 
morpholine, and alkanol amines. Examples of suitable inorganic bases 
include ammonia, NaOH, KOH, and LiOH. 
Suitable acids for adjusting pH include various known organic and inorganic 
acids such as acetic acid, hydrochloric acid, and phosphoric acid. 
The rate of addition of the base or acid to the latex emulsion is usually 
not important. Sufficient base or acid should be added to achieve 
dissolution of the first-stage polymer. The degree of dissolution of the 
first-stage polymer can be estimated by measuring the change in optical 
density (O.D.) of the emulsion before and after addition of the 
pH-adjusting agent. 
For various applications, it is sometimes desirable to employ small amounts 
of various known additives in the latex. Typical examples of such 
additives are bacteriocides, antifoamers, etc. Such additives can be added 
in a conventional manner to such latexes. 
The resulting stabilized emulsion can be used to produce a variety of 
coatings known in the art, including films, polishes, varnishes, paints, 
inks, and adhesives. 
The process of this invention can typically be conducted as semi-continuous 
polymerization as follows. Unless otherwise specified, percentages shall 
refer to weight percent. 
GENERAL PREATION EXAMPLE 
Internally subjected to a nitrogen (N.sub.2) atmosphere, a suitable reactor 
is filled with water and emulsifier and stirred until a homogeneous 
solution is formed. The solution is heated, utilizing conventional heating 
equipment, to the desired reaction temperature. 
The first-stage monomers and chain-transfer agent are combined to produce a 
first-stage mixture. A pre-charge of about 15% of the first-stage mixture 
is introduced into the reactor. An initiator, dissolved in water, is 
thereafter added into the reactor to induce the pre-charge to polymerize. 
The balance of the first-stage monomers and chain-transfer agent are 
thereafter slowly added to the reaction mixture, over a time period of 
about 20 minutes to 2 hours. 
Assuming that an acidic monomer is included in the first-stage mixture, the 
pH of the first-stage emulsion-polymerization reaction mixture is 
optionally raised to about 4.5 to 7 to cause the first-stage polymer to 
"swell" (If a desired second-stage polymerization mixture has not been 
prepared beforehand, such can now be prepared.) 
Thereafter, and over a time period of about 60 minutes, the second-stage 
polymerization mixture (of second-stage monomers) is added at the desired 
reaction temperature. After a short holding period of about 5 to about 30 
minutes, the pH of the reaction mix is slowly raised (over ca. 50 minutes) 
to about 8 to 10 to release the first-stage polymer into solution. 
Alternatively, it might be desirable to prepare a so-called "master" batch 
of first-stage polymer and subsequently utilize such in conjunction with 
certain desired second-stage polymerization reactions. 
The following examples are intended to better illustrate the invention but 
are not intended to limit the scope thereof. 
EXAMPLE 1 
To a 1-liter round-bottom flask fitted with a paddle stirrer and containing 
500 g of H.sub.2 O at 80.degree. C. under a N.sub.2 atmosphere was added 
0.5 g of the emulsifier sodium lauryl sulfate. Next, 1.0 g of the 
free-radical initiator (NH.sub.4).sub.2 S.sub.2 O.sub.8 was added to the 
flask. First-stage monomer, namely 80 g of ethyl acrylate (EA) and 20 g of 
methacrylic acid (MAA), was added over a time period of 30 minutes, along 
with the addition of 2.0 g of the chain-transfer agent butyl 
mercaptopropionate. The monomer-containing mixture was then held at 
80.degree. C. for approximately 15 minutes. The second-stage monomer, 
namely 100 g of methyl methacrylate (MMA), was added into the thus-heated 
monomer-containing mixture over a time period of 30 minutes. The resultant 
mixture was thereafter held at 80.degree. C. for 1 hour with stirring. The 
pH of the stirred mixture was approximately 2.5, and the optical density 
(O.D.), measured on a Bausch and Lomb Spec 70 unit (at 500 nm in a 10 mm 
cell at 0.2% N.V.) was found to be 1.4. 
Next, the pH was adjusted to 9.5 using a 28 weight-percent aqueous ammonium 
hydroxide solution (28 wt.-% aq. NH.sub.40 H soln.). The second-stage MMA 
polymer was stabilized by dissolution of the first-stage EA/MAA polymer. 
The O.D. after pH adjustment was found to be 0.37. 
The relative O.D. values of the thus-produced emulsions as well as the 
actual size of the relative emulsion polymer particles were reduced, which 
provided evidence of dissolution of the inverted first-stage shell. 
EXAMPLE 2 
The procedure of Example 1 was followed, except that 100 g of styrene (S) 
was used as the second-stage monomer in place of the 100 g of MMA. Similar 
results were obtained; and an emulsion latex was formed. When the O.D. was 
measured at a pH of approximately 2.5, the O.D. was found to be greater 
than 2. After adjustment to approximately pH 9, the O.D. was found to be 
reduced to 0.82. 
EXAMPLE 3 
The procedure of Example 1 was again followed, except that no emulsifier 
was added to the first-stage polymerization step. Similar results were 
obtained. When measured at a pH of approximately 2.5, the O.D. was found 
to be 0.4. After adjustment to approximately pH 9, the O.D. was found to 
be 0.18. 
EXAMPLE 4 
To provide a clear model to show inverse core/shell emulsion polymerization 
and also to obtain additional confirmation of release and stabilization of 
the domains by base solubilization of the first stage, a monomodal 
first-stage alkali-soluble emulsion polymer was formulated as follows. 
Such an emulsion was made via a so-called "seeded" approach, wherein a 
fine particle size 80/20 EA/MAA polymer, made by emulsion-polymerization 
techniques, was used as the "seed" for the second-stage manufacturing step 
of the same composition. 
The resulting alkali-soluble, relatively low molecular weight thus-produced 
"seed" was then characterized, at low and high pH, utilizing known 
transmission electron microscopy (T.E.M.) techniques and was shown to be 
both monodisperse, 94 nm (nanometers), and alkali-soluble. Such a seed was 
then utilized in connection with second-stage monomers of both styrene (S) 
and methyl methacrylate (MMA) at 5:1 and 1:1 S/MMA weight ratios, and 
resultant mixtures were subjected to emulsion polymerization. 
When measured at a pH of approximately 2.5, the O.D. of each such mixture 
was found to be 1.1. After adjustment to approximately pH 9, the O.D. of 
each such mixture was found to be 0.66. 
The resulting emulsions were then characterized by known T.E.M techniques. 
In all cases, phase inversion was noted. At high pH, the EA/MAA 
first-stage polymer was shown to be in a dissolved state and the discrete 
second-stage domains remained. These results correlated well with the 
particle size distributions at low and high pH. The distributions tended 
to show lower, monomodal particle sizes at high pH, indicating the 
presence of the second-stage domains after the EA/MAA phase was 
solubilized. The T.E.M. analytical results also correlated well with the 
observation of the lower O.D. value of the emulsions after the pH was 
raised from 2.5 to 9. 
EXAMPLE 5 
To a 1-liter round-bottom flask equipped with a conventional paddle 
stirrer, and internally subjected to a N.sub.2 atmosphere, was added 48 g 
of water and 0.8 g of sodium lauryl sulfate emulsifier (28%). These 
ingredients were then mixed until homogeneous, while heating to a 
temperature of 80.degree. C. 
The following first-stage monomers were next combined along with 2.6 g of 
the chain-transfer agent bromotrichloromethane, to produce a first-stage 
monomer mixture: 
______________________________________ 
Methyl methacrylate 76.7 g 
Butyl acrylate 19.8 g 
2-Ethylhexyl acrylate 19.8 g 
Methacrylic acid 15.9 g 
______________________________________ 
Fifteen percent, namely 20.2 g, of the thus-produced first-stage monomer 
mixture was then added to the reaction flask, as a pre-charge. With the 
temperature of the flask contents at 80.degree. C., 2 g of the initiator 
ammonium persulfate (APS), pre-dissolved in 5 g of water, was added to the 
reaction flask. 
After reacting the pre-charge ingredients at 80.degree. C. for 10 minutes, 
the balance of the chain-transfer agent-containing first-stage monomer 
mixture was added to the flask, over a time period of 30 minutes, while 
maintaining the desired 80.degree. C. reaction temperature. 
After the addition of the remainder of the first-stage monomer mixture to 
the flask was completed, the resultant reaction mixture was held at 
80.degree. C. for one additional hour. Then, a premix of 10.1 g of an 80% 
aqueous solution of 2-dimethylamino-2-methyl-i-propanol, 1.4 g of 28 wt.-% 
aq. NH.sub.4 OH soln., and 20 g of water was added to the reaction 
mixture, using the same feed rate as for the first-stage monomer mixture. 
After such addition was completed, the resultant reaction mixture was then 
held at 80.degree. C. for 5 minutes. The pH was thereafter found to be 
7.0-7.5. 
While the first-stage polymer mixture was reacting, the following 
second-stage monomer mixture was prepared: 
______________________________________ 
Methyl methacrylate 91.4 g 
Butyl methacrylate 157.5 g 
2-Ethylhexyl acrylate 66.5 g 
______________________________________ 
The second-stage monomer mixture was then added to the thus-neutralized 
first-stage polymer mixture, over a time period of 60 minutes, at a 
temperature of 80.degree. C. After such addition of the second-stage 
monomer mixture was completed, the resultant batch was held at a 
temperature of 80.degree. C. for 5 minutes. 
Next, a pre-mix of 5.6 g of 28 wt.-% aq. NH.sub.40 H soln. and 20 g of 
water was added at the same feed rate as for the second monomer feed. The 
resultant reaction mixture was then maintained at 80.degree. C. for 50 
minutes. 
The resulting latex emulsion was thereafter cooled and filtered. The 
emulsion was observed to exhibit the characteristics of an "inverted" 
core-shell emulsion, within which the first-stage polymer had become 
solubilized. 
EXAMPLE 6 
The procedures of Example 5 were again followed, except that the following 
second-stage monomers were employed: 
______________________________________ 
Methyl methacrylate 28.4 g 
Styrene 63.0 g 
Butyl methacrylate 157.5 g 
2-Ethylhexyl acrylate 66.1 g 
______________________________________ 
Results similar to Example 5 were obtained. 
EXAMPLE 7 
A latex for use in a floor polish, which can provide both the low molecular 
weight leveling resins and the high molecular weight colloidal components, 
can be made from the latexes produced according to the present invention, 
using known procedures and formulations. 
As an example, an emulsion polymer was prepared according to the above 
general preparation example (2-hour first-stage monomer addition) 
utilizing the following raw materials: 
Step 1: Preparation of Emulsion Polymer 
______________________________________ 
Stage 1 monomers: 
Styrene 72.0 g 
Acrylic Acid 48.0 g 
Iso-octyl Mercapto propionate 
4.8 g 
Stage 2 monomers: 
Styrene 210.0 g 
Butyl Acrylate 56.0 g 
Methacrylic Acid 14.0 g 
Aqueous phase: 
Sodium Lauryl Sulfate 12.0 g 
Ammonium Persulfate 4.0 g 
De-ionized Water 575.0 g 
______________________________________ 
Step 2: Floor Finish Prepared Employing Step 1 Polymer 
An 18.7% non-volatile, high-gloss floor polish was formulated, in a 
conventional manner, from the above emulsion. The ingredients are listed 
below; 
______________________________________ 
Ingredients 
______________________________________ 
Water 121.4 g 
Non-ionic emulsifier* 2.5 g 
(Triton X 405) 
1% Fluorocarbon Leveling 1.3 g 
Surfactant (Zonyl FSJ) 
28% NH.sub.4 OH (aq. soln.) 
5.8 g 
Oleic Acid 1.3 g 
26% Non-volatile Wax 39.8 g 
Emulsion (a 1:1 blend of 
AC-392 and Eplene E-43 
polyethylene waxes) 
20% Zinc Ammonium Carbonate 
3.0 g 
Solution 
Emulsion polymer 72.6 g 
______________________________________ 
Footnote: 
*The identified emulsifier, Triton X 405, is a commerciallyavailable 70 
wt. % soln. of a 40EO octylphenol surfactant. 
EXAMPLE 8 
An architectural coating was prepared using the polymer prepared according 
to Example 5. The coating had the following formulation: 
______________________________________ 
Paint Base: 
Propylene Glycol 176.3 g. 
Disperse Ayd W22.sup.1 29.39 g. 
Drew Plus T4500.sup.2 5.88 g. 
Water 53.78 g. 
Titanium Dioxide (Kronos 2190) 
734.65 g. 
Paint: 
Paint Base 100.0 g. 
Polymer From Example 5 216.0 g. 
Anti-foam (BYK 073) 0.6 g. 
Dibutyl phthalate 3.8 g. 
______________________________________ 
.sup.1 "Disperse Ayd W22" is a blend of anionic and nonionic surfactants, 
sold by Daniel Products, Jersey City, NJ. 
.sup.2 "Drew Plus T4500" is an antifoam agent for waterbased paints, base 
on mineral oil and a silica derivative, sold by Drew Ameroid. 
The above paint possessed good gloss as well as good coating and adhesion 
properties. 
The next three examples are directed to the production of adhesives. 
EXAMPLE 9 
A first-stage hydrophilic polymer emulsion was produced as follows. To a 
2-liter round-bottom flask fitted with a conventional paddle stirrer and 
containing 580.7 g of water at 80.degree. C. under a N.sub.2 atmosphere 
was added 8.0 g of a first emulsifier, sodium lauryl sulfate, together 
with 8.5 g of a second emulsifier, sodium dodecyl diphenyl oxide 
disulfonate. Next, 2.0 g of the free-radical initiator (NH.sub.4).sub.2 
S.sub.2 O.sub.8 was added to the flask contents. Thereafter, first-stage 
monomers, namely, 310.0 g of ethyl acrylate (EA) and 78.0 g of methacrylic 
acid (MAA), were added to the agitated flask contents over a time period 
of 60 minutes, along with 7.8 g of the chain-transfer agent butyl 
mercaptopropionate. The monomer-containing agitated flask contents were 
then held at 80.degree. C. for 30 minutes; and, thereafter, 5.0 g of a 28 
wt.-% aq. NH.sub.40 H soln. was added, to maintain a pH value of from 5 to 
6. 
Next, the second-stage polymer was produced as follows. To a 2-liter 
round-bottom flask fitted with a conventional paddle stirrer and 
containing 366.7 g of water at 78.degree. C. under a N.sub.2 atmosphere 
was added 100 g of the first-stage hydrophilic polymer-containing emulsion 
along with 15 g of a 4-mole-EO nonyl phenol surfactant. Next, 1.3 g of the 
free-radical initiator (NH.sub.4).sub.2 S.sub.2 O.sub.8 was added to the 
flask. Thereafter, second-stage monomer, namely 10 g of MAA, 433 g of 
butyl acrylate (BA), and 4 g of 1,4-hexanediol diacrylate, were 
simultaneously added to the agitated flask contents over a time period of 
90 minutes. The resultant mixture was then held at 80.degree. C. for one 
hour, while maintaining agitation. The pH of the thus-agitated emulsion 
was approximately 5.5 and the viscosity was approximately 75 centipoises 
(cps). Next, the pH of the thus-agitated emulsion was adjusted to 7.0-7.5, 
utilizing 5.0 g of the above-mentioned 28 wt.-% aq. NH.sub.40 H soln. 
With the addition of the NH.sub.40 H solution, the first-stage EA/MAA 
polymer particles were observed to dissolve in their emulsion and the 
viscosity of such an emulsion was observed to increase to approximately 
1000 cps. 
The thus-produced pH-adjusted second-stage polymeric emulsion was 
thereafter applied to commercially-available polyester film to provide a 
one-mil thick dry film of pressure-sensitive adhesive possessing so-called 
"removable performance" characteristics (i.e., the adhesive and so-called 
"face stock" onto which the adhesive is coated are together cleanly 
removable from a surface). The dried film was observed to have a 
glass-transition temperature (Tg) of minus 48.degree. C. When the adhesive 
side of the adhesive-coated polyester film was applied to a stainless 
steel panel, such was observed to provide an initial 30-minute 180-degree 
peel value of 22 ounces per inch width. (PSTC-1, 180-degree peel, modified 
for residence time of 30-minutes dwell.) 24-hour aging of the polymeric 
adhesive on the stainless steel panel at 70.degree. C. provided a peel 
value of 26 ounces or less. (PSTC-1, 180-degree peel, modified for a 
residence time of 24 hours at 70.degree. C. The Polyken Tack value of the 
polymeric adhesive was observed to be 420 g or less per square centimeter 
(Polyken Probe Tack Test, A-1-1); and the rolling-ball tack (Rolling Ball 
Tack Test, PSTC-6) was observed to be 5 inches or less. 
EXAMPLE 10 
The procedure for Example 9 was repeated except that 4.3 g of diethylene 
glycol dimethacrylate was utilized to produce the second-stage polymer, in 
lieu of the 4.0 g of hexanediol diacrylate. An emulsion polymer, similar 
to that of Example 9, was formed. The initial 30-minute 180-degree peel 
value was determined to be 48 ounces per inch width; the 70-degree C., 
24-hour aged 180-degree peel value was observed to be 110 ounces; the 
Polyken tack was observed to be 600 g per square centimeter; and the 
rolling-ball tack was observed to be 4 inches. 
Thus, while Example 9 produced a "removable" pressure-sensitive adhesive, 
Example 10 produced a somewhat more "permanent" pressure-sensitive 
adhesive. 
EXAMPLE 11 
A heat-sealable (e.g., blister-pack) variety of adhesive was prepared as 
follows. 
The above-discussed procedures of Example 9 were again followed to produce 
yet another quantity of the first-stage hydrophilic polymer emulsion. 
Another second-stage hydrophobic polymer was then produced as follows. 
To the 2-liter round-bottom flask, which was fitted with the conventional 
paddle stirrer and which contained 270 g of water at 78.degree. C. under a 
N.sub.2 atmosphere, was added 250 g of the first-stage hydrophilic 
polymer-containing emulsion along with 15 g of a 4-mole EO nonyl phenol 
surfactant. Next, 1.3 g of the free-radical initiator (NH.sub.4).sub.2 
S.sub.2 O.sub.8 was added to the flask. Thereafter, second-stage monomer, 
namely 10 g of MAA, 225 g of BA, and 150 g of methyl methacrylate (MMA), 
were simultaneously added to the agitated flask contents over a time 
period of 90 minutes to produce a second-stage monomer mixture. The 
thus-produced second-stage monomer mixture was then held at 80.degree. C. 
for one hour, while maintaining agitation. The pH of the thus-agitated 
emulsion was approximately 5.5 and the viscosity was approximately 30 
centipoises (cps). Next, the pH of the thus-agitated emulsion was adjusted 
to 7.0-7.5, utilizing 12.5 g of the 28 wt.-% aq. NH.sub.40 H soln. With 
the addition of the NH.sub.4 OH solution, the first-stage EA/MAA polymer 
particles were observed to dissolve in their emulsion, and the viscosity 
of such emulsion was found to have increased to approximately 1900 cps. 
This emulsion was then reduced to 40 wt.-% solids with water, resulting in 
a viscosity of 85 cps. The pH-adjusted second-stage polymeric emulsion was 
thereafter applied to commercially-available so-called "SBS" paper stock 
to provide a dry film of heat-sealable adhesive. When the adhesive-coated 
paper stock was heat sealed onto rigid PVC blister stock for 11/2 seconds, 
at 50 pounds (per square inch gauge) and at a temperature of at least 
121.degree. C., an adhesive bond was formed that required complete "fiber 
tear" (i.e., failure) of the SBS paper stock to separate the PVC blister 
material from the SBS paper stock. 
What has been described herein is a novel, stable emulsion polymer and 
methods for preparing the same. It will be apparent that the foregoing 
examples illustrate certain preferred embodiments and are not limitative 
of scope. Thus, while the polymer and the methods of the present invention 
have been described with reference to preferred embodiments, the present 
invention is not limited thereto. On the contrary, alternatives, changes 
and modifications will become apparent to those skilled in the art upon 
reading the foregoing description. For example, as Examples 9 through 11 
illustrate, the present invention can be utilized to prepare certain 
adhesives. Still other variations will be obvious to those skilled in this 
art. Accordingly, such alternatives, changes and modifications are to be 
considered as forming a part of the invention insofar as they fall within 
the spirit and scope of the appended claims.