Method of making a coating and a permselective membrane, ionic polymer therefor, and products thereof

This invention relates to an ionic polymer, method for making a coating and a composite membrane therefrom and also relates to products derived from the disclosed methods and polymer. A new lipid-like permselective membrane is disclosed comprising an ultra-thin selective coating deposited on a non-selective but permeable substrate, which may be anionic or cationic, in hollow fiber, tubular or planar form. The method of preparation of the membrane comprises treating the permeable substrate with a solution of the ionic polymer. The polymer is the product of an aromatic monomer, acrylate and vinyl chloride quaternized with a tertiary amine in which at least one of the alkyl groups of the amine contain at least two carbon atoms. The polymer can also be the product of an aromatic monomer and acrylate and the polymer being partially sulfonated. The treatment produces an extremely thin coating that is held tenaciously by electrostatic forces and the hydrophobicity of the polymer determines its permeability. The membrane has improved flux and selectivity.

TECHNICAL FIELD 
This invention relates to a polymer for making anionic and cationic 
coatings for use on oppositely charged substrates. Not only is the 
invention directed to this polymer and method for making a coating and a 
membrane, but is also directed to a coating and membrane product. The 
membrane product is useful in the separation of ammonia from salts, 
alcohols from brines or iodine from salt. 
BACKGROUND 
The present invention is directed to a polymer containing ionic 
functionality which produces an extremely thin, that is, ultra thin, 
coating which is preferably a surface coating layer or film. The prior art 
has failed to teach or suggest such a polymer or polymer coating, in 
particular, on an oppositely charged substrate, which can be used as a 
membrane. We have discovered that improved flux and selectivity 
characteristics are obtained with our membrane compared to known 
membranes. Unlike known membranes, our membrane is formed by coating a 
charged substrate with an oppositely charged polymer coating to form a 
substantially neutral interface between coating and substrate. 
U.S. Pat. No. 3,083,118 to Bridgeford contains shot-gun teachings 
concerning a polymer-modified material with anion and cation-exchange 
sites. This material is used to form thick, charged films. Monomers that 
are polymerized are, for example, styrene butyl acrylate and vinyl 
chloride. A multi-component catalyst system is used: Fe.sup.++ /H.sub.2 
O.sub.2. The reference further generally relates to monomers containing 
tertiary alkyl groups and alkyl amines used to make polymers containing 
ion-exchange groups. However, our invention is directed to a membrane 
product having an ultra thin coating layer which obtains improved 
selectivity and flux. These improved characteristics are not obtained 
using thick, charged films. 
U.S. Pat. No. 3,647,086 contains disclosure relating to a cation-exchange 
membrane, where primary and secondary amines, including dodecylamine, are 
reacted with sulfonated polystyrene on a neutral substrate with subsequent 
conversion of free amine groups into acid amide bonds. However, this is 
not our invention. 
Quaternizing a halogenated polystyrene with tertiary amine containing alkyl 
groups with twelve or more carbon atoms to form microporous or 
ion-exchange membranes is known, by U.S. Pat. Nos. 3,852,224 and 
4,262,041, respectively. 
It is also known to form ion-exchange membranes having a thickness of as 
small as 0.5 microns by dipping, coating or spraying a polymer on a 
substrate, by U.S. Pat. Nos. 3,510,418; 3,945,927 and 4,360,434. However, 
our invention relates to an ultra-thin coating layer, having a thickness 
substantially less than 0.5 micron, on a substrate to form a membrane 
having a substantially neutral interface between coating and substrate. 
Composite membranes, formed by coating a porous substrate with a thin film, 
are known in the art by U.S. Pat. Nos. 3,808,305 and 4,125,462. Substrates 
include ultrafiltration, reverse osmosis or electrodialysis membranes or 
other conventional filtration materials. 
As mentioned, the present invention relates to a polymer containing ionic 
functionality useful in forming an ultra-thin lipid layer which can be 
used to constitute a membrane, having a substantially neutral interface 
between coating and substrate. The polymer, method of using the polymer, 
and the coating and the membrane product thereof, having improved 
selectivity and flux characteristics, distinguish from the background art. 
SUMMARY OF THE INVENTION 
The present invention relates to a method for making a permselective 
membrane comprising polymerizing a mixture selected from aromatic monomer, 
acrylate and vinylbenzyl chloride, which polymer being quaternized with a 
tertiary amine containing alkyl groups having C.sub.1 to C.sub.20 carbon 
atoms, in which at least one alkyl group has at least two carbon atoms, 
and from aromatic monomer and acrylate, which polymer being partially 
sulfonated, and depositing the polymer on an oppositely charged, permeable 
substrate to form an ultra-thin coating thereon forming a permselective 
membrane having high flux and high selectivity. 
The present invention relates to a method for making a permselective 
membrane comprising polymerizing a mixture of aromatic monomer, acrylate 
and vinylbenzyl chloride, quaternizing the polymer with a tertiary amine 
containing alkyl groups having C.sub.1 to C.sub.20 carbon atoms, in which 
at least one alkyl group has at least two carbon atoms, and depositing the 
quarternized polymer on an oppositely charged, permeable substrate to form 
an ultra-thin coating thereon forming a permselective membrane having high 
flux and high selectivity. 
The invention further relates to a method for making a permselective 
lipid-like membrane for separating ammonia from salt, alcohol from brine 
or iodine from salt comprising polymerizing a mixture of styrene, butyl 
acrylate and vinylbenzyl chloride with a quaternary ammonium salt and 
ferric halide/hydrogen peroxide catalyst in deionized water to form a 
water insoluble polymer, quaternizing the polymer with 
dimethyldodecylamine and electrostatically depositing the quaternized 
polymer on the surface of an anionic, permeable substrate forming an 
ultra-thin coating thereon forming a permselective lipid-like membrane 
having high flux and high selectivity. 
The invention further relates to a permselective membrane for fluid 
purification comprising a charged, ultra-thin coating of a polymer of 
aromatic monomer, acrylate and vinylbenzyl chloride quaternized with a 
tertiary amine containing alkyl groups having C.sub.1 to C.sub.20 carbon 
atoms, in which at least one alkyl group has at least two carbon atoms on 
an oppositely charged, permeable substrate forming a permselective 
membrane having high flux and high selectivity. 
The invention also relates to a method for making an ultra-thin lipid 
coating comprising polymerizing a mixture of aromatic monomer, acrylate 
and vinylbenzyl chloride, quaternizing the polymer with a tertiary amine 
containing alkyl groups having C.sub.1 to C.sub.20 carbon atoms, in which 
at least one alkyl group has at least two carbon atoms, and forming an 
ultra-thin lipid coating. 
The invention further relates to an ultra-thin lipid coating comprising a 
quaternized polymer of aromatic monomer, acrylate and vinylbenzyl chloride 
quaternized with a tertiary amine containing alkyl groups having C.sub.1 
to C.sub.20 carbon atoms, in which at least one alkyl group has at least 
two carbon atoms. 
The invention also relates to a polymer comprising aromatic monomer, 
acrylate and vinylbenzyl chloride quaternized with a tertiary amine 
containing alkyl groups having C.sub.1 to C.sub.20 carbon atoms, in which 
at least one alkyl group has at least two carbon atoms. 
The present invention relates to a method for making a permselective 
membrane comprising polymerizing a mixture of aromatic monomer and 
acrylate and partially sulfonating the polymer and depositing the polymer 
on an oppositely charged, permeable substrate to form an ultra-thin 
coating thereon forming a permselective membrane having high flux and high 
selectivity. 
The invention relates to a method for making a permselective lipid-like 
membrane for separating ammonia from salt, alcohol from brine or iodine 
from salt comprising polymerizing a mixture of styrene and butyl acrylate 
to form a water insoluble polymer, partially sulfonating the polymer and 
electrostatically depositing the polymer on the surface of a cationic, 
permeable substrate forming an ultra-thin film thereon forming a 
permselective lipid-like membrane having high flux and high selectivity. 
The invention further relates to a permselective membrane for fluid 
purification, comprising a charged, ultra-thin coating of a sulfonated 
polymer of aromatic monomer and acrylate and partially sulfonating the 
polymer on an oppositely charged, permeable substrate forming a 
permselective membrane having high flux and high selectivity. 
The invention also relates to a method for making an ultra-thin lipid 
coating comprising polymerizing a mixture of aromatic monomer and acrylate 
and partially sulfonating the polymer forming an ultra-thin lipid coating. 
The invention further relates to an ultra-thin lipid coating comprising a 
sulfonated polymer of aromatic monomer and acrylate. 
The invention relates to a polymer comprising aromatic monomer and acrylate 
and partially sulfonating the polymer. 
DETAILED DISCLOSURE OF THE INVENTION 
The invention relates to a new polymer, method for making an ultra-thin 
polymer coating and product thereof and also relates to a method for 
making a composite membrane and composite membrane product thereof. Thus, 
an ultra-thin, lipid-like fluid purification membrane can be fabricated 
utilizing the teachings of this invention. These membranes are prepared by 
treating an anionic or cationic substrate with an ionic polymer containing 
cation or anion functionality, respectively. 
Cationic polymer is prepared by polymerizing the following reactants: 
Aromatic monomer 
Acrylate 
Aromatic vinyl chloride 
Quaternary ammonium salt 
Ferric solution 
Hydrogen chloride 
Hydrogen peroxide 
Mercaptoethanol 
Water 
The reaction product of this polymerization is quaternized with a tertiary 
amine, for example, dimethyldodecyl amine. The resulting quaternized 
polymer can be used to form ultra-thin coatings to be coated on anionic 
substrates. The product can be used in fluid purification, for example, 
desalination and separation of ammonia from salt, alcohol from brine and 
iodine from salt. 
The aromatic monomer can include styrene, vinyl toluene, t-butyl styrene 
and equivalent compounds known to those skilled in the art. 
The acrylate reactant can include butyl, methyl, ethyl, ethyl hexyl 
acrylates, methylmethacrylate and other acrylates known to those skilled 
in the art. 
The aromatic vinyl chloride reactant can include vinylbenzylchloride or 
other known vinyl chlorides. 
The other reactants are conventional and optional. Equivalent reactants are 
known to those skilled in the art. 
The amine reactant includes (CH.sub.3).sub.2 R.sub.1 N; CH.sub.3 R.sub.1 
R.sub.2 N; R.sub.1 R.sub.2 R.sub.3 N; where R.sub.1, R.sub.2, R.sub.3 
=C.sub.1 to C.sub.20, except where R.sub.1 =R.sub.2 =R.sub.3 =C.sub.1, 
which is a methyl group. Thus, the amine compound can include, for 
example, dimethyldodecyl, dimethyldohexyl, triethyl and similar compounds. 
All parts and percentages are by weight unless otherwise indicated. 
Regarding the concentration of aromatic monomer in the reactant, the 
operating range is between about 0 and 99%, the preferred operating range 
being between about 0 and 95%. Regarding the concentration of the acrylate 
reactant, the operating range is between about 0 and 99%, the preferred 
operating range being between about 0 and 95%. Concerning the 
concentration of quaternary amine, the operating range is between about 1 
and 50%, the preferred operating range being between about 5 and 40%. 
The concentration of other components included in the reaction mixture used 
in the polymerization are conventional and known to those skilled in the 
art. 
The polymerization reaction conditions are conventional to those skilled in 
the art, as well as the conditions for quaternization of the polymer. 
Techniques for depositing the quaternized polymer as an ultra-thin coating 
layer on an anionic substrate are also conventional to those skilled in 
the art and include dipping, coating and spraying. 
Anionic polymer is prepared by polymerizing the following reactants: 
Acrylate 
Aromatic vinyl chloride 
Anionic catalyst 
Anionic surfactant 
Mercaptaethanol 
Water 
Polymerization is performed utilizing the above reactants in a conventional 
manner. Thereafter the polymer is coagulated, separated and dried. The 
polymer is then dissolved in a conventional solvent and partially 
sulfonated by adding a sulfonating agent. 
The anionic coating is formed as described above for the cationic coating. 
Also, the cationic substrate is coated in the manner described above for 
the anionic substrates. Overall, this description is similar to and 
reference is made to the description of preparation of the cationic 
polymer for additional details about preparation of anionic polymer 
coating on a cationic substrate. There are, however, additional details. 
The anionic catalyst can be sodium persulfate, potassium persulfate, 
ammonium persulfate or other equivalent catalysts. 
The anionic surfactant can be sodium lauryl sulfate, dihexyl sodium 
sulfonate or other equivalent surfactants. 
The concentrations of the catalyst and surfactant are conventional to those 
skilled in the art. The concentration of the sulfonating agent is between 
1 and 25% and preferably between 5 and 20%. 
Polymer useful in forming thin lipid coatings have an important biological 
function in controlling flux of water, salts and non-electrolytes into and 
out of cells. Ultra-thin lipid coatings are useful in a variety of 
engineering applications. The above-described polymer is useful in the 
preparation of a new type of lipid-like membrane. These new permselective 
membrane structures are prepared by depositing an ultra-thin selective 
layer on a relatively non-selective but permeable substrate. The substrate 
is anionic or cationic in preferably a hollow fiber or tubular form. 
Although, the form also can be planar. Treatment of at least one of the 
surfaces of the substrate with a solution of an ionic polymer containing 
anionic or cationic functionality produces a composite membrane with 
selective permeability. This treatment produces an extremely thin surface 
coating that is unexpectedly tenaciously held by electrostatic forces. The 
hydrophobicity of the polymer, which is controlled by its composition, 
determines the permeability of the composite membrane. While an unmodified 
membrane shows high permeability to hydrophilic ions such as Na.sup.+, 
Li.sup.+, Ca.sup.2+, H.sup.+ and the like, the new composite membrane is, 
in general, much less permeable to such ions. More particularly, such 
membranes show over three orders of magnitude less permeability. On the 
other hand, the thin barrier coating is still quite permeable to such less 
polar species as ammonia, alcohols and iodine. Therefore, the composite 
membranes of the present invention are able to make clean separations of, 
for example: 
Ammonia from salt, 
Alcohol from brine, and 
Iodine from salt. 
Other uses include separation of metal ions, organics from water, 
inorganics from water and salts, inorganics from organics, gases and the 
like. The present invention is advantageous over the prior art. The 
present technology provides an ultra-thin lipid coating easily. This 
coating has good flux, permeation and selectivity characteristics. 
Furthermore, the lipid-like surfaces can be easily rejuvenated. 
Rejuvenation can be accomplished by cleaning with water and contacting 
with polymer solution. 
The substrate can be an anionic or cationic charged substrate. Anionic 
substrates can be, for example, sulfonated polyethylene, ion-exchange 
beads and the like. Conventional cationic substrates are used within the 
purview of this disclosure. Other equivalent substrates known to those 
skilled in the art can be conveniently utilized. 
The ionic polymer coating of the present invention is deposited as an 
ultra-thin layer having a thickness from about 20 to about 300 A, 
preferably about 20 to about 100 A. One or more surfaces of the substrate 
can be coated or the entire substrate impregnated with the coating polymer 
of the present invention. 
The membrane of this invention is advantageously formed into desired shapes 
by casting planar film of the membrane onto a suitable surface and 
removing solvent therefrom. The film may be, for example, flat, concave, 
convex, or in the form of hollow fibers, as previously mentioned. 
The membrane has a minimum thickness such that it is essentially 
continuous, that is, there are essentially no pinholes or other leakages 
in it. It is preferable to prepare a membrane as thin as possible in order 
to maximize the permeation rate while insuring the integrity of the 
membrane. The thickness of the membrane is advantageously in the range 
from about 0.1 to about 250 microns, preferably from about 10 to about 50 
microns. Mechanical strength can be imparted to the membrane by affixing 
the membrane to a porous supporting material. 
Organic polymer coatings have been used to separate polar from non-polar 
species out of water. The separation derives from the preferential 
solubility of the non-polar species in the coating. However, the coatings 
are often times thick and flux rates are low. According to the present 
invention, the selective coating is extremely thin. The composite membrane 
shows high flux as well as high selectivity. The new technology provides 
an ultra-thin coating easily. It can be easily rejuvenated.

The following experiments illustrate the polymer, methods and products 
described above, and also illustrate the ease of formation of the 
ultra-thin lipid coatings, their good flux, permeation and selectivity and 
ease of rejuvenation. These experiments are merely illustrative and are 
not considered to limit the present invention. 
PREATION OF POLYMERS 
Example 1 
Polymerization is carried out in a one liter, 5-necked flask fitted with a 
stirrer, N.sub.2 inlet tube and a condenser. The following reaction 
mixture is used: 
______________________________________ 
Parts/ To be Charged 
100 Parts Monomer 
Material (g) 
______________________________________ 
363.5 Deionized H.sub.2 O 
290.8 
14.0 Trialkyl Quatenary 
11.2 
ammonium salt (5% 
solution) 
50.0 Butyl acrylate 40.0 
(50 mole %) 
23.2 Styrene (28 mole %) 
18.6 
26.8 Vinylbenzyl chloride 
21.4 
(22 mole %) 
5.0 Fe.sup.3+ solution 
4.0 
(0.05%) 
5.0 N/10 HC1 4.0 
10.0 H.sub.2 O.sub.2 (30% solution) 
8.0 
2.5 Mercaptoethanol 
2.0 
______________________________________ 
All the ingredients, with the exception of H.sub.2 O.sub.2 and 
mercaptoethanol, are loaded in the flask and stirred at 200 rpm while 
N.sub.2 is bubbled into the mixture for 20 minutes. Heating is started, 
keeping a positive pressure of N.sub.2 throughout the polymerization. When 
the temperature levels off at 65.degree. C., the polymerization is 
continued for two hours. The latex is, then, cooled and filtered through a 
325 mesh screen. 
The above latex is then quaternized as follows: in a 32 oz. glass bottle, 
100 g latex, 8 g dimethyldodecylamine and 172 g water are combined and 
agitated in a shaker for 4 hours and then kept overnight. After the 
reaction is complete, water is evaporated and final drying carried out in 
an oven at 105.degree. C. The dried resin is dissolved in 50/50 
toluene/t-butanol mixture to get a 3% solution. 
Example 2 
The polymer solution of Example 1 is then used to demonstrate its 
usefulness in making anionic surfaces hydrophobic. The hydrogen form of 
DOWEX 50W.times.8 (30-50 mesh) is washed with deionized water several 
times in a Buchner funnel and the moist resin stored in a bottle. DOWEX is 
a trademark for a series of synthetic ion-exchange resins made from 
styrene-divinylbenzene copolymers, having a large number of ionizable or 
functional groups attached to this hydrocarbon matrix. One gram of this 
resin is contacted with a dilute solution of the polymer in an organic 
solvent, sucked dry and washed several times with distilled water. The 
coated beads are then put in a beaker containing 100 g deionized water and 
stirred with a magnetic stirring bar. Ten grams of 1M NaCl are added and a 
stopwatch started simultaneously. An exchange reaction between Na.sup.+ 
(derived from NaCl) and H.sup.+ (derived from the resin) takes place. This 
fractional Na.sup.+ -H.sup.+ exchange is determined as a function of time 
by titrating the released H.sup.+ with 0.1 M NaOH. Half-time (t1/2) for 
the exchange reaction is determined by plotting milliequivalents (meq) of 
NaOH versus time in minutes. The half time is determined to be 900 
minutes. In a control experiment, uncoated beads give a half time of only 
0.7 minutes. Thus, the ultra-thin layer is several orders of magnitude 
effective in slowing down Na.sup.+ -H.sup.+ exchange. 
Example 3 
In the manner of Example 1, several quaternary polymers are prepared and 
tested as in Example 2. Polystyrene is also included as a control. 
______________________________________ 
Styrene Butylacrylate 
Quaternary t 1/2, 
(mole %) (%) Amine (%) (minutes) 
______________________________________ 
Control 0.7 
(uncoated beads) 
100 0 0 1.5 
70 0 30.0 80-100 
80 0 20.0 80-100 
90 0 10.0 80-100 
16.5 60.8 22.7 1400-1600 
30 60 10.0 500-600 
______________________________________ 
Example 4 
Several quaternary polymers are prepared, but quaternized with 
triethylamine and tested. 
______________________________________ 
Styrene (mole %) 
Quaternary Amine (%) 
t 1/2 (minutes) 
______________________________________ 
Control (uncoated 0.7 
beads) 
95 5 11.0 
90 10 22.0 
80 20 38.0 
______________________________________ 
PREATION AND TESTING OF COMPOSITE MEMBRANE UTILIZING IONIC POLYMERS 
Demonstrating Effect of Surface Modification 
About 50" of polyethylene intramedic tubing PE 50 (0.023" ID; 0.038 OD) is 
wound onto a spindle and sulfonated in a solution of chlorosulfonic acid 
in methylene chloride to a capacity of about 1.5 meq/g. 
The membrane is then placed in a stirred bath of N/10 HCl and N/10 NaCl 
pumped down the fiber, thus causing Na.sup.+ to exchange for H.sup.+ 
across the membrane. The effluent is collected and the hydrogen ion 
content measured by filtration. At a flow rate of 0.46 mls/min, the 
[H.sup.+ ] in the effluent is 0.055N. 
The inside of the tubing is then treated with a solution of a 
styrene/vinylbenzyl quaternary (90:10) and the Na.sup.+ /H.sup.+ exchange 
experiment is repeated. The [H.sup.+ ] in the effluent is only 0.004N, 
indicating the marked effectiveness of the surface treatment. 
Composite Membrane as a Means of Separating Na.sup.+ and NH.sub.4.sup.+ 
A sulfonated coil is pumped with a mixture of NaOH and NH.sub.4 OH with HCl 
in the external bath. The concentrations of Na.sup.+ and NH.sub.4.sup.+ in 
the effluent as a function of flow rate are determined (FIG. 1). The 
membrane passes Na.sup.+ preferentially. The inner surface of the membrane 
is then treated with styrene/vinylbenzyl quaternary.sup.+ (90:10) polymer, 
as previously described, and the membrane exchange experiment repeated. 
The results are illustrated in FIG. 2, where it is clear that the membrane 
is now allowing ammonia to pass while very effectively blocking the flux 
of sodium. 
Extraction of Iodine 
A composite membrane prepared by treating the inner surface of a coil of 
NAFION, a trademark for a perfluorosulfonic acid membrane, with a 
styrene/butylacrylate/vinylbenzl quaternary polymer is fed with a solution 
of molecular iodine while the coil is immersed in a bath of 1N NaOH. The 
treated coil effectively blocked both the leakage of salts into the 
caustic bath and of NaOH into the iodine feed while permitting extraction 
of iodine into the bath (FIG. 3). 
An untreated coil, however, is ineffective in transporting I.sub.2 into the 
bath. Rather, sodium hydroxide leaks into the feed side, causing the 
I.sub.2 to disproportionate to anionic species I.sup.- and IO.sub.3.sup.- 
which are effectively blocked by the cation-exchange membrane. 
This experiment demonstrates the utility of these composite membranes as a 
means of extracting and concentrating iodine. They are superior in flux, 
compared to a totally organic membrane such as polyethylene. 
Example 5 
The preceding experiments were repeated utilizing a polyvinylbenzyl 
trimethyl ammonium chloride cationic polymer. The result shows that this 
polymer did not possess the required high flux rates nor high selectivity 
characteristics of the amphiphilic polymer of the present invention. 
It is not intended to limit the present invention to specific embodiments 
described above. It is recognized that other changes may be made in the 
formulation and methods of application and product thereof specifically 
described herein without deviating from the scope and teachings of the 
present invention. It is intended to encompass all other embodiments, 
alternatives and modifications consistent with the present invention.