r
INTERFACIAL POLYMERIZATION IN A POROUS SUBSTRATE AND
SUBSTRATES FUNCTIONALIZED WITH PHOTOCHEMICAL GROUPS
The invention relates to methods of interfacial
polymerization and to novel products made possible by such methods,
such as membranes.
Membranes are used, for instance, in separation processes
as selective barriers that allow certain chemical species to pass,
i.e., the permeate, while retaining other chemical species, i.e.,
the retentate. Membranes are used in many applications, for
example as inorganic semiconductors, biosensors, heparinized
surfaces, facilitated transport membranes utilizing crown ethers
and other carriers, targeted drug delivery systems including
membrane-bound antigens, catalyst-containing membranes, treated
surfaces, sharpened resolution chromatographic packing materials,
narrow band optical absorbers, and in various water treatments
which involve removal of a solute or contaminant, for example
dialysis, electrolysis, microfiltration, ultrafiltration and
reverse osmosis.
There is a myriad of supports or substrates for
membranes. Specific physical and chemical characteristics to be
considered when selecting a substrate include: porosity, surface
area, permeability, solvent resistance, hydrophilicity,flexibility
and mechanical integrity. Other characteristics may be important
in certain applications.
As 'the use of porous membranes increases, so does the
need to find new ways to modify, or functionalize, the membrane or
~~~~ ~~~
2
membrane substrate. Without modification, effectiveness of the
membrane is restricted by the nature of the membrane or membrane
substrate material itself. Conversely, modification or
functionalization of the surfaces of the membrane substrate can
increase the usefulness of the substrate and can open up new areas
of application.
There are already known methods of functionalizing the
internal pore surfaces of a porous substrate. One method is
radiation grafting, which has the advantage that a wide variety of
monomers can be used which permit further modification.
Disadvantages with this method are that the radiation may degrade
the substrate itself and the method requires expensive equipment.
Another method of functionalizing is 'the coating method which has
the advantage of being a simple procedure and is available for a
variety of polymers. However, the coating method often results in
blocking of the pores of the substrate and generally it is
necessary to post crosslink in order to anchor the polymer to the
substrate, otherwise the finished membrane may be unsuitable for
use with some solvents as the solvents may remove the coating of
the membrane from the membrane substrate. Another method involves
the use of pre-functional resin to make the substrate which is then
converted into some desirable end product substrate. This is a
simple method but functionality is wasted throughout the bulk of
the membrane. Further, post crosslinking may be needed if the
membrane is to be used with solvents. Yet another method is
oxidative derivatlzation which is simple but is limited in the
2~~~'~~'~
3
choice of substrate. Further, the substrate may be degraded and
there is insufficient control of the functionality.
There is no single method of functionalizing internal
pore surfaces that is ideal for every situation. There is always
a need for additional methods to modify, functionalize or form
active surfaces for membrane applications.
Interfacial polymerization has been used to prepare thin
film composite membranes. Interfacial polymerization is a process
in which a very thin film can be made by reacting two, or more,
monomers at an interface between two immiscible phases. It is best
described by example. "Nylons" belong to a class of polymer
referred to as polyamides. One such polyamide is made, for
example, by reacting a diacid chloride, such as adipoyl chloride,
with a diamine, such as hexamethylene diamine. That reaction can
be carried out in a solution to produce the polymer in resin form.
Alternatively, the reaction can be carried out at an interface by
dissolving the diamine in water and floating a hexane solution of
the diacid chloride on top of the water phase. The diamine reacts
with the diacid chloride at the interface between these two
immiscible solvents, forming a polyamide film at the interface
which is rather impermeable to the reactants. Thus, once the film
forms, the reaction slows down drastically, so that the film
remains very thin. In fact, if the film is removed from the
interface by mechanical means, fresh film forms almost instantly
at the interface, because the reactants are so highly reactive with
one another.
2~J~~1~~
The discovery of interfacial polymerization in the late
fifties provoked interest from the textile industry. Natural fiber
textile manufacturers, particularly wool manufacturers, were
looking for ways to make their textiles shrinkproof. In early
experiments wool swatches were soaked in a diamine, excess diamine
was squeezed out by passing the fabric through nip rollers, and
the fabric was soaked in an acid chloride polymerizable with the
diamine.
Numerous condensation reactions that can be used to make
polymers interfacially have been described. Among the products of
these condensation reactions are polyamides, polyureas,
polyurethanes, polysulfonamides and polyesters. Factors af:~ecting
the making of continuous, thin interfacial films include
temperature, the nature of the solvents and co-solvents, and the
concentration and the reactivity of the monomers. Refinements
which have been developed include the use of "blocked" or protected
monomers that can be later unblocked to alter the chemistry of the
finished film or membrane, the use of post-treatment of the films
to alter their chemistry, and the use of heteroatoms in the
monomers to alter the properties of the final film or membrane.
In the classical organic chemistry sense, these alterations or
modifications can be referred to as changes in the functionality,
i.e., in the available functional groups of the monomers and/or
polymers, hence functionalization.
5
The use of interfacial polymerization to produce
extremely thin film on a support is known. Such polymerization can
be carried out by dissolving one monomer in a solvent and then
using that solution to saturate the substrate. The outer surface
of the substrate, saturated with the first solution, is then
exposed to a second solution, immiscible with the first solution,
containing a second monomer. A very thin film of polymer is formed
at the interface of these two solutions on the outside surface of
the substrate.
In the above process, the substrate serves as a
mechanical support for the thin film formed by interfacial
polymerization. The thin film itself extends across and blocks
any pores present in the substrate. Thus this use of interfacial
polymerization does not take advantage of the great surface area
available within a porous substrate.
According to one aspect of the present invention there
is provided a method of preparing a porous article, which method
comprises:
contacting a porous substrate with a first reactant that
enters pores of the substrate; and
contacting the porous substrate bearing the first
reactant with a second reactant that is capable of reacting with
the first reactant in an interfacial polymerization reaction;
the amounts of first and second reactant being selected
such that there occurs no, or substantially no, closing of pores
of the substrate.
According to another aspect of the present invention
there is provided a porous article bearing a compound which is
photochemically reactive and capable of undergoing a substantially
non-reversible chemical transformation upon exposure to ultra-
violet, visible or near infra-red irradiation.
According to a further aspect of the present invention
there is provided a method of functionalizing a substrate which
comprises contacting the substrate with, or forming thereon, a
polymer which is photochemically reactive and capable of undergoing
a substantially non-reversible chemical transformation upon
exposure to ultra-violet, visible or near infra-red irradiation.
According to a further aspect of the present invention,
there is provided a derivatized porous article and a product of a
photochemically reactive moiety on surfaces of said porous
substrate.
According to another aspect of the present invention
there is provided a method of derivatizing a porous substrate which
comprises irradiating an article bearing a compound which is
photochemically reactive as defined above wherein the irradiation
is at a wavelength within the range from ultraviolet to near infra-
red.
According to a further aspect of the present invention
there is provided a method of separation comprising passing a fluid
comprising a compound to be separated through a porous article
bearing a compound which is photochemically derivatized as defined
CA 02099727 2002-O1-24
60557-4437
7
above.
According to ;mother aspect. of the present
invention there is provided a met=hod of conducting a
chemical reaction which comprises pa~;sing a fluid through a
derivatized porous art.i~~le as defined above wherein the
fluid comprises a compound to be reacted and the article
comprises a catalyst fo:r the reaction of the compound to be
reacted.
According to ~~till another aspect of the present
invention, there is provided a porou~~ article comprising a
porous substz,ate havir~.g a polymer deposited on the pore-
defining surf: aces thezve«f, the de~~osi.ted polymer leaving the
pores unblocl~:ed and having photocreemi.c:ally reactive groups
capable of undergoing a substantially nonreversible chemical
transformation to proz~i~~e functional groups on the pore
surfaces upon exposure tc> ultra-violet, visible and near
infrared irradiation at wavelengths which avoid light-
induced detez-ioration of the substrate.
The substrate can take many forms. Examples
include fibex-s, hollow fibers, films, beads, woven and non-
woven webs, spun thre~ids and microcapsules. Suitable
substrates may be pol~.emeric, ceramic:, cellulosic (such as
paper), glassy, metallic or carbonaceous. Eor instance a
suitable sub~~trate may :oe a monolithic substance that is
penetrated by pores. Such a monolitruic substrate may be
formed, for example, x~y extraction of phase--separated
polymers, by extractic:n of soluble particles from a
polymeric matrix or bar sintering f ine particles of a
suitable mate rial.
Alt:ernativel.y, the substrate may be formed from
fibers, for instance in woven form or in non-woven felted
CA 02099727 2002-O1-24
60557-4437
7a
form. Woven and non-wc>v~=n webs may have either regular or
irregular physical corifiguration:~ and provide large surface
areas. Non-woven fibrous webs are easy t:o manufacture,
inexpensive and allow f«r variation i.n fibre density and
texture. A wide variet:~ of fibre diameters, e.g., 0.05 to
50 microns, c:an be used. Web thic.kne~ss can vary widely to
fit the application, E~.~~. , 1 omicron t.c> 1000 microns or more.
Maor surface; o.f a substrate may be planar or
curved,
8
whereas complex surfaces may be tentacular, jagged, uneven,
undulating, irregular or asymmetrical. For example, a porous
planar object or porous bead appears to have outer surfaces which
are planar or spherical, respectively, as their major surfaces.
But on a microscopic scale, the porous planar object or porous bead
has a complex three dimensional geometric configuration. In another
example, a non-woven web or matrix may appear to be flat and to
have a planar major configuration. But on a microscapiC scale, the
surfaces of the web are an unpatterned layering of strands which
give the non-woven web a complex geometric configuration. The
poxes of the web, membrane or bead are uneven, irregular, and
unpatterned in all 'three dimensions.
The pores of the porous substrate are the spaces, voids '
or interstices, provided by the microscopic complex three-
dimensional configuration, 'that provide channels, paths or passages
through which a fluid can flow.
The polymer formed by the interfacial polymerization of
the present invention is located on such surfaces defining such
pores but does not cover, block, clog or fill such pores to any
substantial extent.
The effective sizes of pores may be at least several
times the mean free path of flowing molecules or particles. A wide
range of pore sizes can be accommodated, e.g., from about one
manometer to about several hundred microns.
For macrofiltration, effective pore sizes of the
substrate may range from about 2 to about 200 microns, more
9
preferably 2 to about 50 microns.
For microfiltration, the pore diameters of the porous
substrate can vary widely but preferably range from 0.01 to 2.0
microns, more preferably from 0.1 to 1.0 microns and particularly
from 0.2 to 1.0 microns. Pore diameters for microfilters are
measured by the bubble-point method according to ASTM F-316.
The porosity or pore volume of a polymeric porous
substrate is preferably from 30 to 950, more preferably from 45 to
85% and particularly from 60 to 80~. Porosity can be derived from
the value of the bulk density of the porous substrate and the
polymer density of substrate polymer according to ASTM D-792.
The thickness of substrate will depend on the intended
use of the membrane product. For many uses, for example
microfiltration, thicknesses ranging from 1 to 1000 microns, more
preferably 10 to 240 microns and particularly 20 to 100 microns,
would be suitable.
Pore size will also affect the use for which the membrane
is suitable. The pore size distribution through the substrate
cross-section may be symmetric or asymmetric. Asymmetric membranes
typically have a higher permeability 'than symmetrical membranes
having similar particle retention characteristics.
The porous substrate may have either a reticulated or a
granular structure. A reticulated structure generally has a higher
porosity than a granular one. A reticulated sub strate has a network
of open interstitial flow channels around fibrous strands. A
cJranular structure is a porous network formed around coalesced
20~J'~~"l
solid particles.
Although we do not wish to be bound by this hypothesis,
our hypothesis is that the method of the present invention enables
positioning of a polymer on the internal pore surfaces of a porous
substrate so that the porous substrate bearing the polymer can
function as a membrane for filtration ar other purposes. The pores
remain substantially free, i.e., unblocked and unclogged by the
deposited polymer. Thus the polymer deposited on the inner pore
surfaces of the substrate is free to assist filtration of a feed
stream, or to interact with species in a feed stream, as the feed
stream passes through or past the membrane.
A substantial portion, preferably all, of the surface
pores of a substrate/membrane formed by the method of the invention
remain open. Ideally, no continuous film or layer is formed over
major outer surfaces of the substrate so that the pores of the
substrate are not blocked.
One aspect of the invention is directed to membranes
composed of porous substrates bearing compounds which are
photachemically reactive. This aspect includes thin-film composite
membranes in which a polymer, for example, comprising the
photochemically reactive group is present in a layer on the surface
of a substrate. In this aspect, it is not always essential that the
deposited polymer does not block pores of the substrate. The
invention does extend, of course, to membranes in which a polymer
comprising a photochemically reactive group is located on the inner
pore surfaces of the membrane and the pores are not blocked.
20~9'~~"~
11
The amount of polymeric coating on the substrate can be
measured by the mass gain, i.e., the increase in weight caused by
the presence of the polymer on the substrate, expressed as a
percentage of the weight of the polymer-free substrate. It is found
that, in general, for a material having a density of 1 gm/cc, a
mass gain of about 500 or more will provide sufficient polymer to
affect the properties of the substrate. It is not usually
necessary, for a material having a density of 1 gm/cc, that the
mass gain exceed about 500. As the mass gain increases there is
an increasing risk of closing of pores of the microporous
substrate, which is undesirable. Usually it is preferred, for a
material having a density of 1 gm/cc, that the mass gain is in the
range of about 10 to 50a, more preferably 12 to 170, but this may
vary depending upon the intended application of the membrane, the
internal surface area and the porosity of the substrate.
The choice of substrate will depend at least partly on
the use. Depending on the use, the substrate may be continuous or
non-continuous, flexible or rigid. An example of a non-continuous
and rigid substrate is a microporous chromatography bead. As an
example of a continuous and flexible substrate there may be
mentioned a microporous polyolefin microfiltration membrane or
paper. Substrates intended for use with photochemically reactive
groups should be sufficiently transparent at the wavelength at
which they are to be irradiated, i.e., the wavelength at which
photochemical transformation of the photochemically reactive groups
is to occur, that the photochemical reaction can be carried out.
2fl99'~2"~
12
For example, polyethylene or polypropylene is sufficiently
transparent at a wavelength of about 350 nm at which photochemical
reaction of a diazoketone group occurs for them to be suitable as
a substrate for the diazoketone group. Non-limiting examples of
polymeric materials suitable as substrate are: polyolefins, such
as polyethylene and polypropylene; polyhalo-olefins; polyurethanes;
polycarbonates; polysulfenes; polyethersulfones; polyamides, such
as nylons; polyimides; polyetherimides; and polydialkenylphenylene
oxides.
Interfacial polymerization may be used to form a variety
of polymers, for example: polyamides, polyureas, polyurethanes,
polysulfonamides, and polyesters, as determined by the monomers or
reactants used, i.e., the first and second reactants. Since the
first and second reactants are usually monomers, they will
sometimes be referred to hereinafter as monomers but it should be
understood that in some instances the first or second reactants
may be di-, tri- or oligameric, rather than monomerlc. Also, the
first reactant may be a mixture of two or more reactants and,
likewise, the second reactant may be a mixture of two or more
reactants.
When the first reactant is in solution the concentration
can vary widely. For example, immediately before contact w:Lth the
second reactant, the concentration of the first reactant may be as
low as 5% (w/v) or as high as 100 % (w/v). Similarly the
concentration of the second reactant can range from 5% to 100%
(w/v). Specific concentrations used can be adjusted depending on
~o~~°~rz~
13
the desired quantity of polymer to be formed.
Polyamides are formed by having a di- or mufti-acid
preferably in the form of its acid halide) in one phase and a di-
or mufti-amine in the other phase. Similarly, polyurPas are formed
from di- or mufti-isocyanates and di- or mufti-amines;
polyurethanes, from di- or mufti-isocyanates and di- or mufti-ols;
polyesters from di- or mufti-acids (preferably in the form of their
acid halides) and di- or mufti--ols; and polysulfonamides from di-
or mufti-sulfonic acids (preferably in the form of sulfonyl
halides) and di- or mufti-amines. These and other suitable
reactants for interfacial polymerization are known and the present
invention will be illustrated by discussion of polysulfonamides
formed from di- or mufti-amines and di-or mufti-sulfonyl chloride
as examples of such reactants.
The presence of mufti-amine or mufti-sulfonyl chloride
will result in cross-linking. Thus, where cross-linking is
desirable and when a diamine is referred to, it is to be understood
that a di-and/or a mufti-amine may be used. Similarly, when a
disulfonyl chloride is referred to, it is to be understood that a
di- and/or mufti-sulfonyl chloride may be used.
As suitable diamines there are mentioned di-terminal
diamines containing from 2 to 22 carbon atoms in a chain, for
example ethylene diamine, 1,8-octanediarnine,1,12-dodecane-diamine
and the like. The carbon chain can be straight or branched and
can contain other functional groups, provided that those functional
groups do not interfere with the required polymerization reaction.
1~
As examples of such other functional groups which do not interfere
with the polymerization there may be mentioned ethers, ketones and
esters. After polymerization, the functional groups may be used
to attach other species to the formed polymer. For example, a
tertiary amine can be converted to a quaternary ammonium salt by
reaction with an alkyl halide. If necessary, functional groups can
be protected during the polymerization reaction and the protective
group subsequently removed. For example, a carboxylic acid can be
protected in the form of one of its esters by reaction with the
appropriate alcohol and, conversely, an alcohol can be protected
in the form of an ester by reaction with a carboxylic acid.
Examples of diamines containing additional functional groups
include secondary amine-group-containing compounds such as
diethylene triamine, triethylene tetramine and the like. It is of
course possible to use mixtures of amines.
Sulfonyl halides, rather than sulfonic acids, are
preferred for reaction with the diamines. Although free acids and
derivatives such as anhydrides and esters can also form amides with
amines, in practice their reaction time in interfacial
polymerization reactions is usually too slow for them to be useful.
Again, 'the disulfonyl halides can contain additional functional
groups provided that they do not interfere with the polymerization
reaction, or provided that the functional groups are present in
protected form during the polymerization reaction. Examples of
suitable di- or trl-sulfonyl halides, include:
2~9J'~~'~
3-diazo-4-oxo-3,4-dihydro-1,6-naphthalene disulfonyl chloride
(DKDSC)
1,3,6-naphthalene trisulfonyl chloride (NTSC)
1,5-naphthalene disulfonyl chloride (NDSC).
When a tribasic acid, such as NTSC, is used, the polymer
formed will include some cross-links. Mufti-amines, such as
triamines or tetramines, will also form cross-links. It is of
course possible to use mixtures of acids or, as mentioned above,
mixtures of amines.
When using an amine and a sulfonyl chloride to form a
polysulfonamide it is preferred that the first reactant is the
amine or a solution of the amine and the second reactant is the
sulfonyl chloride or a solution of the sulfonyl chloride.
Suitable solvents for the amine include water or polar,
preferably highly polar, organic solvents.
Suitable solvents for the sulfonyl chloride include non-
polar solvents such as hydrocarbons or halogenated hydrocarbons,
for example, carbon tetrachloride. The choice of solvent is
limited only by its ability to dissolve the monomers and to form
a sharp phase boundary. A mixture of solvents can be used. If a
mixture is used, one of the solvents may be present, for example,
to enhance polymer deposition e.g. chloroform can enhance
deposition of polysuTfonamide.
Solvents completely or relatively inert toward the
particular porous substrate are naturally preferred.
It is possible to apply some reactants, for example
16
volatile acid halides, in the vapor phase, without solvent.
The reactants can be selected so that the formed polymer
contains functional groups. Examples of such groups include
chemically reactive groups, e.g. amino, hydroxy, carboxy and the
like; and those that impart hydrophilicity, e.g. a polyethylene
glycol; hydrophobicity, e.g, a long chain alcohol such as dodecyl
alcohol; oleophobicity, e.g. perfluorododecyl alcohol; ionic
character, e.g. a quaternary ammonium salt, or a Carboxylate or
sulfonate; catalytic activity, a.g. an enzyme; and photoreactivity,
e.g. a diazoketone.
Of importance axe compounds containing photochemically
reactive groups. Such photochemically reactive functional groups
may conveniently be illustrated by the types of reaction they
undergo. These reactions include: (a) photochemical fragmentation;
(b) photochemically induced isomerization; (c) photochemical
generation of acidic species; and (d) photochromiC reactions.
Photochemical fragmentation reactions yield Chemical
intermediates such as ketenes or free radicals.
A ketene, formed by photolysis of a diazoketone, can
undergo subsequent addition to a nucleophil.e. For example, when
the nucleophile is an amine, a thiol, an alcohol or water, the
addition yields an amide, a thioester, an ester or a carboxylic
acid respectively. Such nucleophiliC addition is illustrated by
2-diazonaphthalenone and its derivatives:
<IMG>
18
Free radicals may be formed by alpha-cleavage of an
aldehyde or ketone or by photofragmentation of a peroxide or azo
compound. These free radicals can, for example, initiate
polymerization of a vinyl monamer. An example of a compound that
will undergo free radical photochemical fragmentation is 2-hydroxy-
2-phenylacetophenone (benzoin):
( H by IS
o ~-C o -~ o
H H
2~9~~2~
19
Photochemically induced isomerization leads to a
conformational change, for example in a polymer chain. Such a
conformational change may be a change in geometric structure, a
change in dipole moment, or the generation of a charge.
Photochemically induced isomerizations include: cis-traps
isomerization; ring-formation or ring cleavage; ionic dissociation;
and hydrogen transfer tautomerism.
An example of cis-traps isomerization is the photolysis
of azobenzene:
N N h--~ N N
20
Ring-formation or ring-cleavage is illustrated with 1,3-
dime-4-methyl-1-(2,4,6-trimethylphenyl)-2,3-pentanedioic acid
anhydrides
H3C CH3 O
CH
CH3
\O by i
\ /
CH ~ CH3
3
Ionic dissociation is illustrated with Malachite Green
leucocyanides
CH3
~ C ~ ~ N~ H3 h~ c~ ~ ~ ~ ~ ~ ~, N~ H3
\ "~ /
CH CN CH3 CH3 CN~ ~ CH3
3
zo~s7z~
Hydrogen transfer tautomerism is illustrated with: 1,4-
dihydroxyanthraquinone:
by
and with the 2-(4-nitrobenzylybenzoate ion:
CH2 ~ ~ N02 f---~ ~ ~ CH ~NOO
COO COON
slow
0
CH NOo+I-~
COO
Photochemical generation of acidic species such as UV-
deb2ockable acid-releasing systems is illustrated with 2,2-
dimethyl-2-~[(9-methylphenyl}sulfonyl]oxy}-1-phenyl-1-ethanone:
H3 iIH2
C C O /f\\ ~ CH ~ C-C + HO j \\ o CH3
3
CH3 O O ~ ~e CH3 O O
An example of a photochromic system is 1',3'-dihydro-
1',3',3'-trimethyl-&-nitrospiro[2H-1-benzopyran-2,2(2H)-indole]s
23
light
(fasi:)~
N02 d~ ask ~ / ~~OQ ~NO
(slow) 2
Cti3 Cit3
colourless blue
All the above groups are contemplated as functional
groups in the first or second reactant and thus can form part of
the polymer formed on the porous substrate. Naturally, the
intermediates and other species formed by the above photochemical
reactions can undergo further nonphotochemical reaction to yield
a wide variety of compounds.
Photochemlcally reactive groups are transformed to their
photochemical products by irradiation at wavelengths between ultra-
violet and near infra-red. The reactions are irreversible in the
sense that the products of reaction do not readily revert to their
starting structure when irradiation ceases. The products axe
transformed to relatively stable products of different
configuration or composition, or they are transformed to unstable
intermediates which spontaneously decompose or react with reactive
compounds in their environment.
In the choice of a ph otochemically reactive group, the
following are desirable featuresr photochemistry which permits
introduction of a range of functional groups from a single
precursor; a photochemical reaction which proceeds efficiently to
give a single product; absorption of light at wavelengths which
avoid light-induced deterioration of the substrate; and absorption
of visible light to minimize the cost of the irradiation source.
24
Functionalization of a membrane by means of photo-
chemically reactive groups is an effective method to improve
membrane performance, as it permits a variety of functional groups
to be introduced into or onto the surfaces of the membrane. The
photochemically reactive group can be converted to other groups of
useful chemical functionality. For example, as mentioned above, a
photochemically reactive diazoketone group can be concerted to: an
ester by irradiation when in contact with an alcohol; an amide by
irradiation when in contact with an amine; and a carboxylic acid
by irradiation when in contact with water. These groups can be
further converted. For example, if 'the diazoketone is irradiated
in contact with a tertiary amine having a terminal hydroxy group,
the resulting ester has the tertiary amine group, which can be
quaternized to form a positively charged, quaternary ammonium,
ionic species. Photochemically reactive groups thus offer the
possibility of conversion to compounds having a specific ionic
charge or specific ionic species. This is useful since some
separations of charged particles are enhanced by the presence of
ionic species in a membrane.
The conversion of photochemically reactive groups to a
variety of chemically useful functional groups offers the
possibility of an "off-the-shelf" membrane versatility allows the
membrane user to adapt the membrane for use with a specific enzyme,
without risking revealing proprietary information to an outside
sauce, such as the membrane manufacturer.
In a preferred embodiment, a porous substrate having
25
pores formed by fibrils and a photochemically reactive compound
which forms a substantially photochemically reactivecontinuous
coating encapsulating the fibrils. Such a substantially continuous
coating is formed when the polymer exists on the pore surfaces of
the substrate as a connected network. The coating is thus linked
to itself about and around structural elements defining the pores
of the substrate,
With regard to the method, the substrate is first
contacted with the first reactant or monomer, which is conveniently
dissolved in a solvent. Tt is a feature of the invention that pores
in the porous substrate remain open. Hence, the amounts of
reactant used to form the polymer in situ must not be so large that
there is formed a continuous film of polymer over major surfaces
of substrate; the polymer is formed on the inner surfaces of the
pores which remain open after removal of solvent. To ensure that
a continuous film does not form over major surfaces, it is
necessary to control the amounts of the fluids or solutions
containing the reactants used to form the polymer, This can be
done, for example, by limiting the amount of the first reactant
that is applied to the porous substrate. Alternatively, excess
first reactant can be applied to the porous substrate and some of
the first reactant, or some of the solvent for the first reactant,
then removed, for instance in a drying step, before the second
reactant is fed to the substrate, to reduce the volume of the first
reactant or first reactant solution to less than that of the pore
volume. Conveniently, an excess can be applied by soaking the
~~99~~°~
2&
substrate in a solution of the first reactant, which may be, for
example, an aqueous solution of the amine.
Evaporation is the preferred way of removing excess fluid
or solvent. With small pore sizes, mechanically squeezing out
excess would be inadequate since capillary forces would tend to
recapture liquid squeezed out of the pores. Mechanically squeezing
may also damage some substrates, and is impossible with rigid
substrates.
The rate of reaction between, for example, a diamine and
a disulfonyl chloride is diffusion controlled, and does not
normally go to 1000 completion. E'urthermore, the reaction between
a diamine and a disulfonyl chloride will lead to release of
hydrogen chloride. Hydrogen chloride will react with amine groups,
creating an acid addition salt and interfering with reaction
between amine groups and acid chloride groups. In some instances
a basic compound, for example pyridine or other non-nucleophilic
base, is added as a scavenger for hydrogen chloride. By routine
experimentation it is possible to determine how much diamine to
load, and subsequently how long to immerse the diamine-loaded
substrate in sulfonyl chloride solution of a particular
concentration to obtain a specified mass gain.
Surface active agents can be added to enhance wetting of
the substrate. Other possible additives include acid acceptors or
scavengers such as bases as are well known in the art. These are
commonly added to the aqueous solution in polyamide-forming
interfacial reactions. Among the commonly used acid acceptors are
27
sodium phosphate, sodium hydroxide, and N,N-dimethylpiperazine,
with or without the addition of surface active agents such as
dodecyl sodium sulfate. Alternatively, an excess of the diamine
can be used to scavenge the acid by-product.
The strength of attachment can be increased with
crosslin~cing by way of some tri-functional monomer in place of
difunctional monomer. Thus the polymer, once formed, is not readily
removed and the membrane product can be used with solvents.
One preferred method for applying a coating to a
substrate by interfacial polymerization is to apply the second
reactant to a substantially solvent-free first reactant. This
method can be called the "dry method". In 'the dry method, a
diamine, for example, is dissolved in a suitable volatile solvent,
for example, methanol. The methanolic solution of diamine is
applied to the substrate. The methanol is then removed by
evaporation. This can be achieved by evaporating the methanol at
room temperature, or the substrate bearing the methanolic solution
can be subjected to reduced pressure, or it can be heated to speed
the evaporation. Of course, if heat is used it should be
sufficiently mild that it does not adversely affect properties of
the substrate which, in some cases, may be heat-sensitive.
When the methanol has been removed there is left on the
substrate the diamine. The diamine-bearing substrate is then
Immersed in a solution of the second reactant, for example, a
dlsulfonyl chloride. When the d:lamlne and the disulfonyl chloride
encounter each other they react to farm, initially, an oligomer
28
that forms an interface. Further reaction is believed to occur as
diamine diffuses through the interface, forming polymer on the
substrate. Normally, in the method of the present invention,
interfacial polymerization would occur, and polymer would be
located, throughout the substrate. The polymer is believed not to
be chemically bound to the substrate, but it does s'arround or
enclose regions of the complex surface of the substrata,
especially in those cases where the amine or the sulfonyl chloride
or both, axe more than difunctional, so that crosslinking occurs.
For the purpose of the present invention, permanent attachment
would be indicated by the inability of aqueous systems or solvents
to remove the formed polymer.
The substrate may be wetted before contact with the first
reactant solution, conveniently with a solvent which is miscible
with the solvent to be used for the first reactant, to assist
uptake of the reactant by the substrate, For example, in the
method using an aqueous solution of diamine, as first reactant,
with a hydrophobic porous substrate, the substrate can be wetted
with methanol before contact with the diamine solution. Another
way to assist reactant uptake by the substrate is to use .reduced
pressure. For example, if the substrate is planar, the reactant
solution is applied to one side of the planar substrate and the
pressure is reduced on the other side, to draw the reactant
solution into the substrate,
Tf the diamine has a short chain, it may have high
surface energy and consequently, may form a ball or bead on the
20~~~~~
29
internal pore surfaces, rather than spread evenly when deposited
on the substrate. When reacting with sulfonyl chloride, there may
be formed a polymer film enclosing unreacted amine which is later
washed out. The resulting polymer film, in this case, may be a
quite rough and irregular coating. This is advantageous when high
surface area or tortuosity in the resulting substrate is desired.
Fox example, when a reactive functionality is incorporated into
the coating. When desired, to avoid this rough coating, a wetting
agent or a surfactant can be incorporated in the solution of
diamine to reduce the surface energy of the diamine and cause it
to spread. Longer chain diamines have lower surface energy and will
therefore spread naturally, not requiring the assistance of a
wetting agent.
EXAMPLES
In the examples, unless stated otherwise, all rinses with
solvent were for 3 minutes with a 50 mL portion of solvent for each
rinse. The porous substrate was a polypropylene suitable for
microfiltration and having the following characteristics: a pore
size of 1.10 microns; a porosity or a void volume of 82.90; and a
thickness of 83.9 microns. Mass gain was calculated as the
difference in weight between the dry untreated substrate and the
dry treated, or polymer-bearing, substrate. The composition of the
polymer-bearing substrate was verified using transmission Fourier
transform infra-red spectroscopy with the substrate compressed at
a pressure of 138 MPa (20,000 psig). Where appropriate, the spectra
were compared with spectra of the untreated substrate. The presence
~o9~~z~
of sulfur and chlorine in the polymer-bearing substrates was
verified by energy dispersive X-ray analysis. Blockage of the pores
was checked with scanning electron microscopy.
Care was taken to avoid contact with light of any monomer
or polymer containing the photochemically reactive 3-diazo-4-oxa
moiety.
Example 1
A 7.6 cm (3 inch} diameter disk was cut from the
polypropylene substrate. The disk was rinsed three times with
acetone. After drying at room temperature, the disk was weighed.
The disk was rinsed with methanol for five minutes to
wet it. After rinsing, the disk was left for thirty minutes in 50
mL of a 10 g/L 1,6-hexanediamine solution in water. The disk was
removed from the diamine solution and its surface was patted to
dry the surface of the disk. The disk was weighed to determine the
diamine solution uptake.
The disk was left at room temperature, allowing water to
evaporate. Evaporation was allowed to proceed until 90o by weight
of the water had evaporated, based on the total weight of diamine
solution taken up by the disk. The disk was then immersed for
sixty minutes at room temperature in 100 mLs of a solution of
sulphonylchlorides dissolved in carbon tetrachloride. The solution
contained 2.5 g/L of a mixture of 3-diazo-4-oxo-3,4-dihydro-1,6-
naphthalene disulfonylchloride (DKDSC} and, to provide cross-
linking, 9.,3,6-naphthalene trisulphonyl-chloride in a weight ratio
of 95s5. Polysulfonamide was formed at the aqueous diamine
31
interface.
The polymer-bearing disk was then rinsed twice with
chloroform and then twice with absolute ethanol to remove residual
unreacted monomer.
The disk was dried at room temperature and weighed.
The mass gain was 15.20. This gain was attributed solely
to polysulfonamide having photochemically reactive groups. Analysis
showed the presence of diazo and sulfonamide groups, indicating
diazo-containing polymer, and an absence of chlorine groups,
indicating absence of unreacted sulfonylchloride monomer.
Polysulfonamide was found to be distributed throughaut
the internal surfaces of the substrate. The pores were essentially
unblocked. Thus the substrate essentially retained its complex
geometric configuration.
Example 2
A disk prepared according to Example 1 was irradiated at
350 nm for thirty minutes (15 minutes per side} while immersed in
20 mL of absolute ethanol to convert the 3-diazo-4-oxo- moiety
first to an intermediate ketene and then, by reaction with the
ethanol, to the corresponding ethyl ester.
The disk was dried at room temperature and weighed.
The mass gain was 5.40. Analysis showed the presence of
carbonyl and sulfonamide groups but showed no diazo groups. This
indicated that the mass gain is attributable to the polymer
resu:Lting from the chemical transformation of the photochemically
reactive polysulfonam:lde to the corresponding ethyl ester.
32
Polysulfonamide ethyl ester was found to be distributed
throughout the pores of the substrate. The pores were essentially
unblocked.
Example 3
A disk of 8.5 cm. (3.4 inch) diameter was cut from the
polypropylene substrate. The disk was rinsed in acetone, dried and
weighed as in Example 1. The disk was immersed for 30 minutes in
50 mL of a 20 g/L solution of 1,8-octanediamine in methanol. The
disk was then removed and left to stand for 30 minutes to evaporate
essentially all the methanol and re-open the pores.
The disk was immersed for 2 hours at 50 C in a solution
of sulfonylchlorides. The solution contained 10 g!L of a mixture
of 3-diazo-4-oxo-3,4-dihydro-1,6-naphthalene disulfonyl-chloride
arid, to provide cross-linking, 1,3,6-naphthalene
trisulfonylchloride in a weight ratio of 95:5. The solvent was a
binary mixture of 40% (vfv) chloroform in carbon tetrachloride. The
purpose of the chloroform was to enhance deposition of polymer.
Polysulfonamide was formed at the interface between the diamine
located on the internal surfaces of the substrate and the
sulfonylchloride solution.
The polymer-bearing disk was rinsed twice each with
chloroform, methanol and de-ionized water to remove monomer,
oligomer and any removable polymer.
The disk was dried and weighed.
The mass gain was 31.4%. This gain was attributed solely
to polysulfonamide having photochemically reactive groups. Analysis
2o~~~z~
33
showed the presence of diazo and sulfonamide groups, indicating
diazo-containing polymer, and an absence of chlorine grougs,
indicating absence of unreacted sulfonylChloride monomer.
Polysulfonamide was found to be distributed 'throughout
the pores of the substrate. The pores were essentially unblocked.
The void volume was found to be 75.6%.
Example 4
A disk was prepared according to Example 3. After polymer
formation, rinsing and drying, the disk was immersed in 20 mL of
de-ionized water and irradiated at 350 nm for 30 minutes {15
minutes each side). The irradiation in water converted the 3-diazo-
4-oxo- moieties to carboxylic acid groups by way of the ketene
intermediate.
The mass gain was 17.1%. Analysis showed the presence of
carbonyl and sulfonamide groups but showed no diaZO Or Chlorine
groups. This indicated that the mass gain is attributable to the
polymer resulting from the chemical transformation of the
intermediate ketene groups of the photochemically reactive
polysulfonamide to the corresponding Carboxylic acid.
Polysulfonamide was found to be distributed throughout
the pores of the substrate. The pores were essentially unblocked.
The void volume was found to be 77.8x.
Examgle 5
A disk was prepared according to Example 3 except that
1,5-naphthalene disulfonylchloride was used instead of the 3-diazo-
4-oxo-3,4-dihydro-1,6-naphthalene disulfonylchloride. The
_.
34
polysulfonamide-bearing substrate thus had no photochemically
reactive groups.
After drying and weighing, 'the mass gain was found to be
l7.Oo.
Polysulfonamide was found to be distributed throughout
the pores of the substrate. The pores were essentially unblocked.
The void volume was found to be 78.40.
Example 6
Particle challenge tests were used to determine the
effect of substrate treatment on the filtration properties of the
porous substrate by comparing a disk of untreated substrate with
disks prepared according to Examples 3, 4 and 5. The tests were
conducted in a dead end stirred cell at a pressure of 13.8 kPa
(2 psig) and a stirring speed of 450 rpm. The particles used for
the test were spheres of polystyrene and of carboxylate modified
polystyrene (obtained from Seradyn Inc., Indianapolis, Indiana).
Samples of spheres had well-defined diameters. Particular diameters
evaluated were in the range of 200 to 500 nm. The particles were
dispersed at a concentration of 100 ppm in a buffer solution of pH
9. The aqueous buffer solution contained: 1.6 g/L ammonium
chloride; 2.0 mL/L ammonium hydroxide (30% aqueous) and 0.05% (m/v)
TritonTHX-100. Scanning electron microscopy was used to examine
the presence of spheres in the pores of 'the substrate.
Scanning electron microscopy revealed considerable
fouling of the untreated control substrate. The substrates prepared
according to Examples 3, 4 and 5 showed substantially no fouling.
2fl9fl"~~'~
The fouling was least when using carboxylate modified polystyrene
spheres with the substrate of Example 4. The absence of fouling
was believed to be the result of the repulsion of the negatively
charged spheres by the negatively charged acid groups of the
polysulfonamide. These results show that functionali.zing a
substrate can significantly alter the properties of the sub~ttrnte.
Examples 7-11
The following examples, although using only model
compounds 111ustrate the products formed on photolysis of
photochemically reactive groups in contact with various
nucleophiles. These examples use the reactive ketene intermediate
formed by photolysis of a diazoketone.
Example 7
R photochemical compound, 5-diazo-5,6-dihydro-6-oxo-t.-
naphthalene-N,N-diethylsulfonamide (I) (0.2 g) and 3-diazo-3,4-
dihydro-4-oxo-1-naphthalene-N,N-diethylsulfonamide (II) (0.2 g)
NEtz SO2NEt2
O ~ \N
2
N2 O
(Il
(zx)
_ ~0~~'~2'~
36
were separately photochemically irradiated at 350 nm for 2 hours
in 120 mL of diethyl ether saturated with water. The solvent was
removed under vacuum. The photochemical products were, as expected,
the corresponding indene-carboxylic acids. The products were
purified from choloroform and n-hexane. The product compounds were
verified and characterized using infra-red, 13C and 1H NMR, and
mass spectral analyses.
Example 8
A photochemical compound, 5-diazo-5,6-dihydro-6-oxo-1-
naphthalene-N,N-diethylsulfonamide (0.2 g) was photo-chemically
irradiated at 350 nm for 2 hours in a solution of 2-bromoethanol
(1 mL; 14 mmol) and 100 mL of diethyl ether. The solution was
washed with 4 x 50 mL of water and dried over anhydrous sodium
sulfate. The ether was removed in vacuum. The photochemical
product was, as expected, the corresponding bromo-ethyl ester of
the indene-carboxylic acid, The product was verified and
characterized using infra-red, 13C and 1H NMR, and mass spectral
analyses.
Example 9
A photochemical compound, 5-diazo-5,6-dihydro-6-oxo-1-
naphthalene-N,N-diethylsulfonamide (0.1 g) was photochemically
irradiated at 350 nm for 2 hours in a solution of ethylene glycol
(15 mL; 0.27 mol) and 85 mL of diethyl ether. The solution was
washed with 3 x 100 mL of water and dried over anhydrous sodium
sulfate. The ether was removed in vacuum. The photochemical
product was, as expected, the corresponding hydroxyethyl ester of
~o~~~z~
37
the indene-carboxylic acid. The product was verified and
characterized using infra-red, 13C and 1H NN~R, and mass spectral
analyses.
Example 10
A photochemical compound, 5-diazo-5,6-dihydro-6-oxo-1-
naphthalene-N,N-diethylsulfonamide (0.1 g) was photochemically
irradiated at 350 nm for 45 min. in a solution of diethylamine (0.1
mL; 0.97 mmol), glacial acetic acid (1 mL; 17.5 mmol), and 100 mL
of methylene chloride. The solution was washed with 3 x 100 mL of
water and dried over anhydrous magnesium sulfate. The ether was
removed in vacuum. The photochemical product was, as expected,
the corresponding N,N-diethyl amide of the indene-carboxylic acid.
The product was verified and characterized using infra-red, 13C and
1H NMR, and mass spectral analyses.
Example 11
A photochemical compound, 5-diazo-5,6-dihydro-6-oxo-1-
naphthalene-N,N-diethylsulfonamide (0.1 g) was photochemically
irradiated at 350 nm for 1.5 hours in a solution of methyl
piperazine (0.1 g), glacial acetic acid (2 mL), and 200 mL of
diethyl ether. The solution was washed with water (3 x 50 mL,
acidic, basic, and neutral) and dried over anhydrous sodium
sulfate. The volume of ether was reduced to 10 mL and impurities
removed by filtration. The ether was removed in vacuum. The
photochemical product was, as expected, the corresponding N'-methyl
piperazine amide of the indene-carboxylic acid. The product was
verified and characterized using infra-red, 13C and 1H NMR, and
20~9'~2'~
38
mass spectral analyses.
Examples 12-27
The effect of the polymer, formed by interfacial
polymerization, on the porosity of the porous substrate was
investigated. The procedure of Example 3 was followed for a number
of control samples using two different concentrations of
octanediamine in the amine solution and varying proportions of di-
arid tri-sulfonyl chloride. The concentration of diamine is
reflected by the mass gain of the final polymer-bearing disk; at
the higher concentration of diamine, more diamine is available for
polymerization with the sulfonyl chloride solution and thus, more
polymer can be formed. The mass gain and the porosity were
determined. In the above range of mass gains, the decrease in
porosity of the porous substrate showed surprisingly little
dependence on the mass gain. That is, a larger mass gain (more
polymer) did not significantly decrease porosity (more blocked
pores). For most samples the porosity was not reduced more than
about 11s and for some samples, not more than about 80. Tha
results are shown in the following table:
20~~7~'~
39
MASS GAIN VS. POROSITY
[1~g_
Octanediamine] [NDSC+NTSC] % NTSC MASS GAIN POROSITY
~J/L) ~g/L)
Example
Untreated 0.0 82.9
12 20 10 10 13.9 80.2
13 20 20 5 14.0 79.7
14 20 10 10 15.2 74.0
15 20 10 5 16.2 78.8
16 20 10 5 17.0 77.1
17 20 20 10 17.4 78.4
18 20 20 5 17.6 73.7
19 20 20 10 17.9 82.9
20 40 20 10 22.3 77.7
21 40 20 10 26.4 77.9
22 40 10 5 35.8 78.0
23 40 10 10 36.0 74.6
24 40 20 5 38.0 76.7
25 40 10 5 38.7 75.5
26 40 ZO 5 38.9 74.9
27 40 10 10 42.9 73.8
2~99~r2'~
The various modifications and alterations of this
invention will be apparent to those skilled in the art without
departing from the scope and spirit of this invention and this
invention should not be restricted to that set forth herein for
illustrative purposes.
