Pan emulsion

Stable emulsions and dispersions of both the water-in-oil and oil-in-water types are prepared by subjecting mixtures of the two phases to shear stress in the presence of nitrile group-containing copolymers capable of forming hydrogels containing at least 90% by weight of water at room temperature.

This invention relates to stable emulsions and dispersions containing a 
polar aqueous phase, a water-insoluble non-polar phase, and an 
acrylonitrile copolymer emulsifying or dispersing agent, and to a method 
of making such emulsions and dispersions. By "stable" is meant emulsions 
and dispersions which do not exhibit phase separation when maintained at 
room temperature for prolonged periods, say 2 days or more. 
BACKGROUND OF THE INVENTION 
Acrylonitrile copolymers capable of forming hydrogels containing at least 
90% by weight of water at room temperature are well known in the art. 
Preferably, the total number of nitrile groups 
##STR1## 
in such copolymers is between 5 and 75 percent (more preferably between 10 
and 50 percent) of all substituent groups present, and at least 1/5 of 
such nitrile groups (preferably at least 1/2 ) are arranged in sequences 
containing at least 5 adjacent nitrile groups; they may be considered 
either graft or block copolymers, preferably the latter. 
One group of such acrylonitrile-based hydrogels is linear polymers having a 
hydrocarbon backbone to which are bonded nitrile groups along with other 
substituent groups such as carboxyl, carboxylate salt, carboxylic ester, 
and amide and imide groups. They may or may not be covalently 
cross-linked. For the most part such copolymers are made by partial 
hydrolysis of polyacrylonitrile (PAN) under appropriate conditions; the 
hydrolysis can be catalyzed by either acid or base. They are described, 
for example, in Stoy U.S. Pat. No. 4,107,121, which is incorporated herein 
by reference. 
Another group of such acrylonitrile-based hydrogels is polysaccharides, 
e.g., starch, grafted with polyacrylonitrile segments (SPAN), which are 
then hydrolyzed with base to acrylic acid or acrylamide segments to form 
the hydrogels. Under certain controlled hydrolysis conditions, however, 
the hydrolyzed copolymer contains residual nitrile groups in sequences of 
5 or more. 
The acrylonitrile copolymer emulsifying and dispersing agents of the 
present invention are those acrylonitrile copolymers which are capable of 
forming hydrogels containing at least 90% by weight of water at room 
temperature, i.e. hydrogels which retain their form and shape without 
liquid flow when allowed to stand at room temperature. Such copolymers 
are, as a rule, not crosslinked by covalent bonds. The three-dimensional 
network in such hydrogels is formed by interactions between the nitrile 
group 
##STR2## 
sequences which form crystalline clusters. The clusters are crystalline 
domains whose structure resembles closely that of PAN itself (for 
instance, the essential features typical for PAN can be detected in X-ray 
diffraction patterns of such hydrogels). The hydrogels can also be formed 
by acrylonitrile copolymers crosslinked covalently to supplement the 
physical network of the type indicated above, although the latter is 
dominant with respect to the important physical properties. 
The emulsions and dispersions of the present invention contain an aqueous 
polar phase and a water-insoluble nonpolar phase. The aqueous phase may 
contain in addition to water various water-soluble polar materials such as 
alcohol, glycols, acids and/or salts thereof, while the non-polar phase 
may contain a variety of water-insoluble solids or water-insoluble 
non-polar liquids with or without water-insoluble solids dissolved 
therein. Examples of important emulsions and dispersions which can be made 
in accordance with the present invention and their uses are milk and other 
food products; food substitutes and additives; latices, both synthetic and 
natural, e.g. latex paints and adhesives; creams, lotions, and ointments 
in cosmetics and health care; cooling and lubricating emulsions, hydraulic 
fluids; emulsion polymerization medium for numerous important monomers; 
liquid membrane systems, drug delivery systems, implantable tissue 
augmentation and many others. Recently, one special group of emulsions 
(liposomes) is being developed for targeted and controlled drug delivery. 
SUMMARY OF THE INVENTION 
It has now been found that stable emulsions and dispersions containing a 
polar aqueous phase and a water-insoluble nonpolar phase can be made by 
mixing said phases with a copolymer of a nitrile group-containing monomer, 
e.g., acrylonitrile, capable of forming a hydrogel containing at least 90% 
by weight of water at room temperature, and subjecting said mixture to 
shear stress. Preferred are emulsions and dispersions made with 
acrylonitrile copolymers capable of forming hydrogels containing at least 
95% water; particularly preferred are those copolymers capable of forming 
hydrogels containing at least 98% water. Also preferred are emulsions and 
dispersions made with such copolymers containing no covalent 
crosslinkages, which copolymers at temperatures above about 50.degree. C. 
are soluble in water to form liquid solutions, not gels. Such emulsions 
and dispersions are highly thixotropic, with viscosity strongly dependent 
upon temperature, and stable both at high and low temperatures. 
The amount or concentration of acrylonitrile copolymer employed can be 
varied over a wide range, as in the case of conventional emulsifiers. As 
little as 0.05% by weight based on the aqueous phase is effective in some 
cases, while amounts up to 5% by weight or even more can be used in 
certain cases; typically, the copolymer concentration ranges from 0.1 to 
2% by weight. The amount desired in any particular case can readily be 
determined by simple experiment. The amount of the nonpolar phase 
preferably is no greater than about 50% by weight based on the total 
composition weight in order to form an oil-in-water emulsion.

Particularly stable are emulsions and dispersions formed in the presence of 
copolymers containing, in addition to the acrylonitrile units, acrylic 
acid salt units. 
The emulsions and dispersions according to the invention are stable under a 
broad range of conditions and can be broken by evaporation of water or by 
a change of conditions which substantially changes the swelling capacity 
of the copolymer used (such as change of pH, salt concentration, addition 
of polymer-precipitating organic solvents, etc.). 
Although oil-in-water emulsions and dispersions are the type most useful, 
water-in-oil emulsions and dispersions are also possible, and both types 
can coexist in one system. 
In addition to the three basic components (i.e. polar aqueous phase, 
water-insoluble nonpolar phase and acrylonitrile copolymer), the emulsions 
and dispersions according to the invention may contain any additives which 
do not destabilize them, such as pigments, ultraviolet absorbents, 
fillers, fragrances, dyes, auxiliary emulsifiers, water-miscible organic 
additives (such as alcohols, glycerine, 1,2-propanediol, 
polyethyleneglycol, saccharides and polysaccharides, proteins and 
components or fragments thereof), drugs and biologically-active compounds, 
preservatives, salts, amino acids, surfactants, radiopaque additives, 
water-soluble polymers or thickening agents to improve the properties and 
utility of such emulsions. Depending upon their characteristics the 
additives may form part of the aqueous phase or of the water-insoluble 
non-polar phase. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
We have found that a non-polar liquid, such as mineral oil, octadecanol or 
corn oil can be emulsified in water containing an acrylonitrile copolymer 
as defined above if mixed under high shear, such as in a blender or even a 
food processor. The emulsions thus formed are stable under a broad range 
of conditions and have certain unusual properties described below. 
The most unexpected property is the emulsion stability itself. The 
acrylonitrile copolymers are composed of sequences of acrylonitrile units 
and sequences of a hydrophilic acrylic acid derivative, such as acrylate 
salt, acrylamide, acrylhydroxamic acid, acrylhydrazide, an hydrophilic 
acrylic ester, and the like. The acrylonitrile sequences are highly polar, 
as witnessed, for instance, by the solubility parameter of 
polyacrylonitrile itself, which has a value of 15.4. Polyacrylonitrile (or 
corresponding sequences in the hydrogel) cannot be considered a non-polar 
or lipophilic moiety by any stretch of the imagination. The hydrophilic 
sequences of the copolymer are also highly polar, and a corresponding 
homopolymer would be water-soluble. Therefore, the non-polar moiety 
conventionally deemed essential for an effective emulsifier is missing 
completely. In addition to that, a hydrogel is both oil- and 
water-insoluble by definition, forming discrete particles with highly 
hydrated surfaces. Therefore, the copolymers are lacking the most 
important and basic characteristics of usual emulsifiers. In spite of 
that, they appear to be very efficient emulsifiers and dispersing agents, 
yielding--even in absence of other emulsifying agents--stable emulsions 
and dispersions. 
Without limiting the scope of this invention, our tentative hypothesis of 
emulsifying or dispersing efficiency of the acrylonitrile copolymers 
assumes that the acrylonitrile sequences are organized in a planar 
conformation with respect to the dipolar nitrile groups, which are engaged 
in complementary interaction with nitrile groups from different sequences 
with opposite orientation. Therefore, each crystalline cluster is composed 
of several layers of nitrile groups in planar conformation. In this way 
the polar forces of the nitriles are mutually compensated and each cluster 
behaves as a non-polar moiety, exposing only the paraffinic backbones to 
the environment. Because such organization is hindered by any covalent 
crosslinking, the non-crosslinked copolymers show higher emulsification 
efficiency. Because the crystalline clusters are not permanently bonded, 
the high shear forces during the mixing can help their rearrangement 
necessary for their sorption on the water-oil interface. 
The nitrile groups should be arranged in sequences of at least 5 in order 
to form such clusters. The total number of nitrile groups in the copolymer 
required for effective cluster formation will vary depending on the length 
of the sequences--as sequence length increases, the total number of 
nitrile groups needed decreases. In general, the total number of nitrile 
groups is preferably between 5 and 75% of all substituent groups present 
and more preferably between 10 and 50%; at nitrile contents above 75%, the 
clusters become too large and rigid to achieve proper orientation at the 
oil-water interface. 
The particular method used to prepare such copolymers is unimportant as 
long as the above-described nitrile sequences are formed. Examples of 
suitable methods include copolymerizing acrylonitrile with hydrophilic 
polymers, grafting acrylonitrile onto a hydrophilic polymer and then 
polymerizing the acrylonitrile, or grafting a hydrophilic monomer onto 
polyacrylonitrile and then polymerizing it. Other suitable methods include 
chemically modifying polyacrylonitrile by partial hydrolysis to form the 
copolymer or chemically coupling a polyacrylonitrile precursor to a 
hydrophilic polymer. 
The clusters probably survive even if a copolymer hydrogel as a whole is 
melted, by which is meant melting of the crystalline PAN domains, which 
causes the hydrogel to lose its coherent three-dimensional structure. This 
could explain the stability of the emulsions at high temperatures when 
viscosity is low (in other words, the system is a true stable emulsion or 
dispersion rather than a dispersion in which phase separation is hindered 
by the high viscosity of the continuous phase). 
The copolymers having low concentration of the nitrile clusters such that a 
hydrogel formed from it can melt in water upon heating appear to be more 
efficient emulsifiers and dispersing agents than those with higher 
concentration of nitrile groups and, therefore, lower hydrogel water 
content and higher melting point. In other words, the emulsifying or 
dispersing efficiency (measured, for instance, by the concentration of the 
polymer necessary to achieve emulsion stability) increases with increasing 
water content in the hydrogel formed by the copolymer. This appears to 
support our hypothesis, because the less organized and more mobile 
clusters can take the thermodynamically advantageous position on oil-water 
interface with ease, while the stronger clusters need more time and energy 
for similar rearrangement. Our hypothesis is supported by the fact that 
emulsions and dispersions made with copolymers capable of forming less 
swellable hydrogels need higher shear and longer mixing time to achieve 
the same stability as those forming weaker hydrogels with higher water 
content. 
The viscosity of emulsions and dispersions according to our invention is 
significantly higher than the viscosity of any liquid component. In 
addition, they are distinctly thixotropic, i.e. their viscosity is much 
higher at rest than when a shear stress is applied. This indicates that 
the polymer chains are sorbed on the oil-water interface on one hand, and 
in mutual interaction on the other. We believe that this is so due to the 
fact that several PAN sequences are on each polymer chain so that they can 
engage in the two types of interactions simultaneously. As a consequence, 
our emulsions and dispersions appear to be structured in more a 
complicated manner than those with other emulsifiers or dispersing agents, 
resembling perhaps liposomes in some respects. 
Since the crystalline domains (which are presumably adsorbed in the oil or 
water-insoluble non-polar phase) and hydrophilic domains cannot be 
physically separated, water is probably present both as continuous phase 
(as in classical emulsions) and as discontinuous phase (i.e. entrapped in 
the water-insoluble non-polar phase via hydrated domains in close vicinity 
of the crystalline domains). 
The high viscosity and thixotropy of our emulsions and dispersions is 
beneficial in many applications. For instance, a skin cream based on our 
emulsions is very easy to spread into a very thin layer, but does not run 
or drip in thick layer, so that it combines the properties of a cream and 
a lotion in an optimum manner. 
Another example of the benefits can be a latex paint based on our emulsion 
or dispersion which has a gel-like consistency while in the can (so that 
the pigments or other particulate components do not sediment), but can be 
sprayed, applied by a brush or a roller as a paint of low viscosity. As an 
additional benefit, our paint does not drip, run, or streak. Also, it is 
stable during freeze/thaw cycling. 
Still another example of the benefits can be the use of our emulsion or 
dispersion in a food or as a food additive. For instance, the emulsion of 
water, vegetable oil and acrylonitrile copolymer can have the consistency, 
look and rheological properties of mayonnaise. The small amount of 
acrylonitrile copolymer plays the roles of emulsifier, thickening agent 
and thixotropic additive simultaneously, thus replacing an array of 
compounds in the natural product. Because the acrylonitrile copolymer is a 
non-toxic, inert additive without any caloric content or nutritional 
function, it could be a suitable dietary alternative for the natural 
product. In addition, the emulsions formed with the acrylonitrile 
copolymer are more stable, and can be boiled, heat-sterilized and stored 
for extended periods of time. 
Another valuable property of the emulsions and dispersions according to the 
invention is their ability to melt reversibly. The viscosity of the 
emulsion or dispersion decreases with increasing temperature more steeply 
than the viscosity of the continuous (aqueous) phase, due to melting of 
the crystalline PAN domains. This is valuable particularly in the case of 
highly viscous, gelatinous emulsions and dispersions, which can be melted 
and cast into any desirable shape. They can also be diluted with water or 
compounded with additives in the molten state without applying shear. 
Still another unique and useful property is the destabilization of the 
emulsion or dispersion by the evaporation of water. As the water 
evaporates, the emulsion or dispersion breaks into a continuous non-polar 
phase. This happens first on the surface, whereupon the thin surface layer 
of non-polar material formed slows down the further evaporation, so that 
the emulsion or dispersion is stable for a long time at ambient (room 
temperature) conditions. This property can be used for the formulation of 
varnishes, polishes, water-proofing of wood or leather, and similar 
applications. Although the emulsion or dispersion can be readily diluted 
with water, washed, etc., once applied in a thin layer on the substrate, 
it is rapidly converted into a smooth and continuous layer of, e.g. wax, 
rosin, crosslinking oil or rubber. 
Another potentially important property is the insolubility of highly 
thixotropic gelatinous emulsions and dispersions in water below their 
melting temperature (i.e. the melting temperature of the crystalline PAN 
domains). Such emulsions and dispersions closely resemble fat in tissue, 
and can be used for tissue augmentation in dermatology and cosmetic 
surgery. Because of its high thixotropy, the emulsion or dispersion can be 
applied subdermally, intradermally or intramuscularly, and will penetrate 
into interstices between the cells. Once at rest, it becomes insoluble and 
fills the space just as natural fat cells would. Because the 
solidification is a purely physical process without any chemical reaction, 
change in osmolarity in surrounding tissue, or release of solvents, the 
application is an atraumatic event. The "synthetic fat" is stable 
(compared to, e.g. collagen), but can be molded by temporarily heating it 
above the melting temperature of the crystalline PAN domains using, e.g. 
ultrasound; removal of the heat source causes the hydrogel to re-solidify. 
The emulsion or dispersion can also be combined with or contain 
water-soluble (e.g. antibiotics) or water-insoluble drugs (e.g. steroids), 
so that the subdermally injected emulsion or dispersion can be used for a 
protracted drug delivery. 
The invention can be illustrated by the following non-limiting examples: 
EXAMPLE 1 
Polyacrylonitrile of molecular weight 350,000 was dissolved in a mixture of 
71% nitric acid and 98% sulfuric acid (mixed in a weight ratio of 9:1) to 
form a viscous solution containing 5 wt % of the polymer. The solution was 
kept at ambient temperature for several days until about 90% of the 
nitrile groups were hydrolyzed to form a PAN copolymer. The reaction was 
then stopped by pouring the solution into excess cold water, so that the 
solution coagulated into a soft, clear PAN copolymer gel containing about 
95% of water after washing. The washed copolymer was dried and ground to a 
fine powder. The copolymer contained about 12% of nitrile groups, more 
than 80% of amide groups, and the balance of carboxylic acid and imide 
groups. X-ray diffraction indicated continuous polyacrylonitrile 
sequences. 
7.5 grams of the powdered copolymer was suspended in 990 grams of cold 
water. The suspension was then heated to boiling until the powder 
dissolved. The solution thus formed was cooled to ambient temperature to 
form a very soft, clear integral gel. The gel could be repeatedly melted 
or dissolved by heating and gelled or solidified by cooling. 
500 grams of pure corn oil was added to the above gel and the mixture was 
mixed in a high-speed blender at ambient temperature for several minutes. 
A stable, creamy emulsion was formed. 
If heated to 100.degree. C., the emulsion's viscosity decreased but no 
phase separation was observed even after extended heating (several days). 
The emulsion gelled upon cooling, its viscosity being substantially higher 
than before or during the heating. The emulsion was also stable under the 
effect of ultrasound. If pushed through the needle of a syringe, the 
emulsion flowed freely but regelled immediately after it exited the 
needle, thus indicating high thixotropy. 
The emulsion was readily dilutable with water in the molten state. It was 
immiscible with water or saline in the gelled state. 
EXAMPLE 2 
One (1) gram of the copolymer from Example 1 was dispersed in 400 grams of 
water and heated until it dissolved. Cooling of the solution did not cause 
it to gell visibly as in Example 1, although the solution viscosity 
increased significantly, indicating the presence of a hydrogel. 
100 grams of octadecyl alcohol was added and the solution was stirred in a 
high-speed blender for about 20 seconds. A stable emulsion was formed. The 
emulsion withstood heating without phase separation. However, it did 
visibly gel upon cooling. 
The emulsion was diluted with water without loss of stability. Also the 
addition of 10% glycerol, ethylalcohol, or isopropanol did not decrease 
the emulsion stability. 
The emulsion served as a base for cosmetic lotion. 
EXAMPLE 3 
Hydrolysis of polyacrylonitrile (MW=150,000) by 3% aqueous sodium hydroxide 
at ambient temperature yielded a copolymer containing amide and carboxylic 
acid units. The copolymer was treated for several hours with 5% sulfuric 
acid, then washed with water to pH about 6. The pellets of copolymer, 
containing less than 50% water, were soaked in a 5% solution of ammonium 
bicarbonate to open cyclic imide groups and neutralize carboxyl groups. 
The copolymer thus formed contained about 70 mole % of nitrile units, 
about 20% of ammonium salt units and about 10% of amide units. .sup.13 C 
NMR spectrum showed that the nitrile groups were organized in continuous 
sequences. The copolymer was soluble in aqueous sodium thiocyanate 
solutions, indicating the absence of covalent cross-linking. If coagulated 
from such solution by pouring it into excess saline it formed a hydrogel 
containing about 91% by weight of isotonic saline. 
The copolymer in pellet form was thoroughly washed, dried and ground to a 
fine powder. Ten (10) grams of the powdered copolymer was dispersed in 1 
liter of water. The suspension was refluxed for several hours, then cooled 
down to ambient temperature to form a slurry. 200 grams of the pasty 
slurry was mixed with 125 grams of glyceryl oleate in a high-speed blender 
for about 20 minutes. A highly viscous, pasty emulsion was formed, which 
was heated in a closed bottle to 90.degree. C. for about 2 hours. Upon 
cooling, a highly thixotropic emulsion was formed. 
The emulsion was added to 500 ml of 0.9% NaCl solution in a blender running 
at a moderate speed. The emulsion particles formed a stable dispersion in 
the continuous aqueous phase, where the "oil phase" contained a 
substantial fraction of water. This "double emulsion" resembled a 
dispersion of liposomes in a number of important respects and could also 
perform similar functions. 
EXAMPLE 4 
A copolymer of acrylonitrile with 7% of methylacrylate (MW=90,000) was 
hydrolyzed by 5% KOH at ambient temperature for about 100 hours, until its 
swelling capacity in the form of a hydrogel reached about 500 to 600 grams 
of water per 1 gram of dry polymer in equilibrium at ambient temperature. 
The copolymer contained less than 20% (mol.) of nitrile units organized in 
blocks of molecular weight about 250 or more, the balance being formed by 
acid salt and amide groups in a molar of ratio about 2:1. The copolymer 
had high absorption in the UV region around 380 nanometers. 
The copolymer was processed as described in Example 3 to form a fine 
powder. Five (5) grams of copolymer was then dispersed in 1 liter of water 
at ambient temperature and stirred for about 1 hour until a fine, viscous 
slurry was obtained. 500 grams of mineral oil and 150 grams of glycerol 
were added to the slurry, and the mixture was blended in a high-speed 
blender for several minutes. Highly viscous, thixotropic emulsion was 
formed which could be reversibly melted by heating above about 50.degree. 
C. to form a creamy liquid. 
Cooling the emulsion caused it to form a gel. The emulsion was stable in 
both the molten and gelled state, and was considerably stable even if part 
of the water evaporated. Evaporation of water caused formation of a rather 
compact gel composed of glycerol-swollen polymer and the oil. In contact 
with water, the gelled emulsion swelled back to its original consistency. 
The emulsion was stable also at freezing temperatures, and could be 
sterilized by autoclaving. 
EXAMPLE 5 
Ten (10) grams of the copolymer from Example 4, 600 grams of water and 400 
grams of a 2% solution of androstanazone in cottonseed oil were mixed in a 
high speed blender until a cheesy, highly thixotropic emulsion was formed. 
The composition could be injected subcutaneously through a hypodermic 
needle, forming a long term deposit of the anabolic steroid. 
EXAMPLE 6 
To compare the effect of an acrylonitrile copolymer on the stability and 
viscosity of latex emulsions, the following two emulsions were prepared 
(Samples A and B). 
Sample A 
Commercial interior white latex paint having the following composition: 
______________________________________ 
TiO.sub.2 (Type 2) 
10.1% 
CaCO.sub.3 6.2% 
Silica/silicates 26.7% 
Vinylacrylic resin 
6.9% 
Additives 1.3% 
Water and glycerols 
48.8% 
______________________________________ 
Sample B 
1 kg of Sample A latex was mixed with 7 grams of the copolymer from Example 
4 and 50 grams of isopropyl alcohol (to help to break bubbles). The 
mixture was homogenized in a high-speed blender for 10 minutes to form a 
highly thixotropic, creamy semi-gel-looking liquid. The aqueous phase of 
the original paint now contained highly swollen hydrogel microparticles. 
The viscosities of Sample A and Sample B were measured using a Brookfield 
viscometer at 25.degree. C. at various shear rates. 
The drawing shows the dependence of viscosity (.eta.) (in cP) vs. shear 
rate (.gamma.) (in RPM) for Sample A (Curve 1) and Sample B (Curve 2). 
FIG. 1 demonstrates that the hydrogel increased emulsion viscosity at shear 
rates up to about 10 RPM. 
The modified latex paint of Sample B could be as easily spread by brush or 
roller as the original paint, but formed a better quality surface if 
applied in a thick layer. There was no paint loss during its application 
because it did not drip from the brush or roller. If applied on vertical 
surface, it achieved the same thickness after one coating as that achieved 
after applying two or three coatings of the original paint. 
While the original paint started to sediment after several hours, the 
copolymer modified paint stayed in the can without any sedimentation for 
several months. The hydrogel additive also increased the emulsion 
stability during freeze-thaw cycling. 
EXAMPLE 7 
0.5 gram of the copolymer from Example 4 was mixed with 500 ml of water and 
700 g of glyceryl stearate in a high-speed blender for about 20 minutes. 
The creamy emulsion thus formed was not dilutable by water but was 
dilutable by oil, indicating a water-in-oil emulsion. 
100 g of this emulsion was mixed with a dispersion of 0.1 gram of the 
copolymer from Example 4 in 200 ml of water. The emulsion reverted into an 
oil-in-water type, while the oil phase retained a substantial amount of 
the polymer and water in it, thus forming a water-in-oil-in-water 
emulsion. 
EXAMPLE 8 
20 grams of polyisobutylene (MW=4,000) was dissolved in 20 grams of 
chloroform and 60 grams of toluene. The solution was blended into a slurry 
of 1.2 grams of the polymer from Example 4 in 200 ml of water in a high 
speed blender. The emulsion thus formed was stable in a closed container. 
If spread in a thin layer, water evaporated and the emulsion converted 
into a thin continuous layer of the polyisobutylene solution. The emulsion 
was useful as a water-dilutable but water-resistant adhesive. 
EXAMPLE 9 
12.0 grams of wheat starch (Hercules Star Bake grade) were dispersed in 250 
grams of distilled water, stirred at 50.degree. C. for 1 hour until 
swollen, and then cooled to ambient temperature. 17.5 grams of distilled 
acrylonitrile and 4.1 ml of an initiator solution (0.1N ceric ammonium 
nitrate in 1N nitric acid) were added to the aqueous starch dispersion 
under a nitrogen blanket. The mixture was homogenized and left overnight 
at 25.degree. C. to allow the acrylonitrile to graft onto the starch. The 
grafted starch (S-PAN) was then extracted with hot water to remove 
unreacted starch and with DMF to remove any acrylonitrile homopolymer. The 
purified S-PAN contained about 57.5% by weight of grafted PAN (determined 
from nitrogen content). The average molecular weight of the PAN graft was 
estimated to be between about 250,000 and 500,000 daltons. 
The S-PAN was washed in water to remove DMF and then centrifuged to remove 
excess water. Next, it was dispersed in NaOH solution (3% by weight) to 
hydrolyze the acrylonitrile units. Hydrolysis was carried out at 
22.degree. C. and monitored by measuring the concentration of NaOH in the 
liquid phase using titration. When 50% of the nitrile groups had been 
converted to carboxyl groups, hydrolysis was terminated by neutralizing 
residual NaOH with dilute sulfuric acid (pH=3.5). The copolymer was then 
centrifuged and washed in water, neutralized with a slight excess of 
ammonium bicarbonate, and finally dried at 60.degree. C. 
The resulting copolymer contained about 40 wt. % of starch and about 60 wt. 
% of graft. The graft consisted of about 50 mol % ammonium acrylate, 25 
mol % acrylamide, and 25 mol % acrylonitrile. NMR analysis indicated that 
the concentration of nitrile groups contained in sequences of at least 5 
or more was at least 10 mol % based on the graft fraction. This copolymer 
is further referred to as Sample A. 
For comparative purposes, S-PAN was also hydrolyzed at 80.degree. C. using 
8.5% NaOH to hydrolyze all nitrile groups as described, e.g., in Weaver et 
al., J. Appl. Polym. Sci. 15:3015 (1971). This fully hydrolyzed S-PAN, now 
referred to as Sample B, was processed in the same fashion as Sample A. 
Five grams of Sample A were dispersed in 995 grams of water, allowed to 
swell for 2 hours at ambient temperature, and then run through a colloid 
mill to get a slurry of fine uniform swollen particles. The slurry behaved 
as a viscous, thixotropic solution (Slurry A). Slurry B was prepared in an 
identical manner. Next, 50 grams of pure corn oil was mixed with 100 grams 
of Slurry A in a high speed blender, and the emulsion thus formed 
(Emulsion A) passed through the colloid mill. It was then stored in a 
closed bottle. Emulsion B was then prepared from Slurry B in an identical 
manner. Although Slurry A and Slurry B looked rather similar, Emulsions A 
and B showed marked differences: 
a. Emulsion A had a higher viscosity than Slurry A, with pronounced 
thixotropic character. Emulsion B had a viscosity similar to that of 
Slurry B. 
b. If left still at an ambient temperature in a closed container, Emulsion 
A was stable over a period of several months. Emulsion B showed signs of 
separation after several hours, and in two days the major part of oil was 
separated in continuous layers. This shows that Emulsion A is a true 
emulsion while Emulsion B is merely a dispersion of oil phase in viscous 
aqueous phase, so that phase separation is merely slowed down. 
c. When heated to 90.degree. C. in a closed bottle, Emulsion A melted into 
a thin, milk-like liquid, but no phase separation could be observed even 
after several hours. When cooled down, the emulsion regained its original 
gel consistency. When Emulsion B was heated, its viscosity was reduced 
just slightly and phase separation accelerated. After 1 hour Emulsion B 
was broken into two immiscible layers which stayed separated after 
cooling. This confirms the observation made above that Emulsion B is not 
thermodynamically stable. 
Because Sample A and Sample B differed only in the presence or absence of 
nitrile sequences, this example illustrates the essential role of the 
nitrile sequences for stability of the emulsions according to our 
invention.