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The present invention relates to a porous material and to a process for its
preparation. In particular the present invention relates to a porous
material whose total pore volume with respect to the overall volume of the
material is within the range 75 to 98% and to a process involving the
preparation of a high internal phase emulsion.
It has previously been proposed in U.S. Pat. No. 4,039,489 to prepare
relatively low density oil absorbent polymeric materials in the form of
polystyrene and polyurethane foams using various foaming agents. In
British Patent No. 1,291,649 proposals have been made to prepare a
relatively low density, oil absorbent, polymeric foam by the inclusion of
a volatile material into a pre-polymer and then rapidly reducing pressure
and permitting the volatile material to expand the polymeric material to
generate the foam.
In U.S. Pat. No. 3,988,508 Lissant has disclosed the production of
polymeric materials by polymerization of an oil-in-water emulsion system
having a high internal phase ratio of monomer to water, preferably 85-95%,
although the disclosure is of monomer water ratios in the range 20:80 to
95:5 without a cross-linking agent.
The study of high internal phase emulsions has been carried out for many
years and the basic theory behind their preparation and structure has been
discussed by K. J. Lissant in "Surfactant Science Series", Volume 6,
"Emulsion and Emulsion Technology", Part 1, edited by K. J. Lissant,
Marcel Dekker Inc., New York, 1974. In this work Lissant discusses the
geometrical packing of droplets in high internal phase emulsions and
suggests that especial care must be exercised in selecting emulsifying
agents for such compositions and that, in the region of 94-97% volume
percentage of internal phase, critical changes occur in the high internal
phase emulsion (HIPE). Beerbower, Nixon, Philippoff and Wallace of Esso
Research and Engineering Company have studied high internal phase
emulsions as safety fuels, such compositions containing at least 97% by
weight of hydrocarbon fuel (ref. American Chemicals Society,
Petro-chemical Pre-prints, 14, 79-59, 1969).
In U.S. Pat. No. 3,255,127, polymeric materials are disclosed which are
prepared by polymerization in reversed emulsion. In this specification a
relatively small proportion of water is emulsified into a mixture of
emulsifier, catalyst and monomer and the emulsion so produced is mixed
into a far larger proportion of water, usually containing a stabilizer
such as polyvinyl alcohol, which keeps the droplets of reversed emulsion
in a relatively stable form. Polymerization takes place in a period of the
order of 24 hours at 55.degree. C. to yield particulate polymer or polymer
block which can readily be broken down to give a particulate polymer.
In British Patent No. 1,576,228 AKZO disclosed the production of
thermoplastic microporous cellular structures comprising microcells having
an average diameter of 0.5-100 microns with smaller diameter pores
connecting the microcells. These structures are made by dissolving a
suitable thermoplastic polymer in a solvent at elevated temperature and
then cooling the solution to solidify the polymer and then removing the
liquid from the thermoplastic polymer structure. This process is clearly
limited in its application to polymers which can readily be dissolved in
appropriate solvents.
In British Patent No. 1,513,939, Ceskoslovenska Akademie Ved also disclosed
the production of porous polymers, but these are formed as porous beads
which may be coalesced to form a moulding which will clearly not be
homogeneous or uniform in its porosity. The porous beads are prepared by
dissolving the polymer to be used in a solvent and then dispersing the
solution into a compatible carrier liquid and this mixture is added to a
coagulating liquid such as water to precipitate the porous beads of
polymer. This process is also limited in that if cross-linked polymers are
desired they can only be produced by a random linking of pre-formed linear
polymer chains.
British Specification No. 2,000,150 discloses the production and use of
cross-linked polymeric porous beads. The beads may be used to extract
components from liquid mixtures and typically have a pore volume of 2.42
ml/g and are hard enough to be packed into absorbency columns.
British Specification No. 1,458,203 suggests the preparation of shaped
cellular articles by curing an emulsion containing up to 90 parts by
weight of water to 10 parts by weight of polymerizable mixture.
In British Patent No. 1,428,125, ICI commented on the desirability of
maximizing the water content of water extended polymers, but they suggest
that difficulty was experienced in obtaining water-in-oil emulsions with
water contents in excess of 88% by weight water.
Our earlier EP patent specification No. 0060138 suggests the preparation of
a porous homogeneous material from a high internal phase emulsion using a
cross-linked vinyl polymer material.
It is an object of the present invention to provide a novel highly porous
polymeric material. It is a further object of the present invention to
provide a novel highly porous polymeric material that can be made by a
process that can be readily adapted to continuous or semi-continuous
production methods.
According to a first aspect of the present invention there is provided a
porous cross-linked polymeric material having cell sizes within the range
100 to 0.5 .mu.m and total pore volume with respect to that of the overall
volume of the material in the range 75 to 98% wherein the polymeric
material includes cross-linked polycondensation polymeric material.
Thus the present invention provides a highly porous cross-linked
polycondensation material having cell sizes within the range 100 to 0.5
.mu.m. The present materials thus differ from conventional foamed for
example polyurethane materials whose cell volumes range from a minimum of
about 200 .mu.m to a selected higher value for example 500 .mu.m. The
present cross-linked materials also differ significantly from those
disclosed in GB No. 1576228 which by necessity are thermoplastic and
non-crosslinked.
The present materials preferably have a total pore volume with respect to
that of the overall volume of the material of at least 85%, more
preferably of at least 90%.
The present materials preferably comprise a structure of interconnecting
cells. The material can thus be very light and can for example have an
overall density of less than 0.25 g/cm.sup.3. A realistic minimum overall
density for a material of 98% overall porosity will be of the order of
0.02 g/cm.sup.3.
In principle there is no inherent restriction on the polycondensation
polymer comprising the present materials. The polycondensation polymer can
thus be chosen from a wide range of materials. For example the
polycondensation polymer can give either a hydrophilic or a hydrophobic
characteristic to the porous polymeric material, and if desired,
functional groups can be present in the polycondensation polymeric
material.
The present polymeric materials can thus have a high porosity and
permeability in combination with a resistance to chemical attack and
dissolution due to their cross-linked nature, the degree of cross-linking
being at least such that the materials retain an integral
three-dimensional matrix even in a solvent swollen state. A range of
mechanical characteristics e.g. tensile strengths, and thermal stability
can moreover be imparted to the material, depending primarily on the
particular polycondensation material selected. Such a combination of
properties at a cell size of 0.5 to 100 .mu.m provides a novel material
for which many advantageous uses can be envisaged.
Examples of such uses include use as a filter body in a wide variety of
environments, use as a carrier for example for a range of catalysts in a
wide variety of physical and chemical environments, and use as a
containment system for example a range of toxic materials in liquid form.
For use as a containment system the present porous materials can either be
prepared having open interconnected cells allowing the toxic or other
liquid to be absorbed to provide a non-spill container or, alternatively,
the porous materials can be prepared having a closed cell system with the
toxic or other liquid comprising the dispersed internal phase and thus
being immediately contained within the porous polymeric material as it is
formed providing a non-spill and non-evaporating containment system.
The present materials can moreover be substantially homogeneous and can be
present in a monolithic block form, particulate form or for instance an
extruded sheet or strand form. The integral nature of the material again
allows a wide variety of uses for the material to be contemplated.
The polycondensation polymeric material can be derived from a monomer
and/or pre-polymer or mixtures thereof having at least two different
reactive groups. In other words the polycondensation species formed can be
of the type --(X--Y).sub.n -- in which X and Y are derived from the
reactive groups. Alternatively the polycondensation polymeric material can
be derived from at least two types of monomers or pre-polymers. In other
words the polycondensation species formed is of the type --(--X--
X--Y--Y--).sub.n -- in which X and Y are derived from the respective
reactive groups on two types of monomer or pre-polymer X'--X' and Y'--Y'.
In some cases the polymeric material can be formed by ring-opening
reactions of cyclic molecules e.g. of the type
##STR1##
By pre-polymer we mean a pre-polymerized group of monomers which can be
chain extended by a polycondensation reaction to form the polycondensation
polymeric material. Cross-linking is inherent due to the number of
reactive groups on the monomer or prepolymer or can be introduced by
appropriate cross-linking agents. The monomers and/or pre-polymers can be
branched and/or straight chain.
Chain-extension or cross-linking can occur by the addition of other
reactive components. For example, poly-condensation cross-linking can
occur by the addition of formaldehyde to a pre-polymer or polymer such as
formed from phenol formaldehyde. Generally the pre-polymers employed will
have a molecular weight within the range 200 to 100,000 and/or chain
length of 2 to 1,000 units, preferably 200 to 20,000 molecular weight
and/or chain length of 2 to 200 units.
A great variety of polymers can be produced by the present process.
Suitable polycondensation reactions are exemplified by the descriptions in
"Condensation Polymers" P. W. Morgan Interscience New York 1965. The
present polymers are suitably derived from synthetic materials,
particularly those obtained from fossil sources e.g. coal or petrochemical
sources or inorganic sources. The present polymers can however be derived
from materials derived from natural sources, which can if desired by
modified e.g. cellulose acetate. Mixtures of sources can be employed.
Particular examples of polycondensation polymeric materials which can be
employed in the present invention include the polycondensation products
between urea and aldehydes, the polycondensation products between phenols
and aldehydes, the polycondensation products between resorcinols and
aldehydes, polyvinyl formals, polyesters, polyamides, polyacetals,
polyurethanes, polysiloxanes, polyimides, polybenzimidazoles, polyethers,
polythioethers, polyketals, polyether sulphones and polyether ketones and
mixtures thereof.
The present polymeric materials can have an overall density of less than
0.25 g/cm.sup.3. A minimum overall density will be of the order of 0.02
g/cm.sup.3. These figures as well as those relating to cell size and pore
volume relate to the initially formed polymeric material. On washing and
drying, the material may collapse resulting in a change in pore
dimensions. On placing in a solvent the material may swell, again
resulting in a change of pore dimensions.
Preferably, the cell sizes can be within the range of 50 to 5 .mu.m, more
preferably 20 to 0.5 .mu.m, even more preferably 10 to 0.5 .mu.m. The cell
sizes can be uniform and readily be of the order of 3.5 .mu.m. Although
some few cells may be present with a size below 0.5 .mu.m, the vast
majority will have diameters within the range 100 to 0.5 .mu.m. Preferably
the cells are interconnected by a plurality of holes in the walls of the
pores. The holes can be of the order of 8 to 16 per cell or the number of
holes per cell can be very much greater. The holes can be of a size in the
range of 0.2 to 0.05 cell diameter.
The present invention can thus provide a highly porous, adsorbent, and
light-weight material. The materials can be generally homogeneous.
Materials can be formed having a dry density of less than 0.25 g/cm.sup.3,
even less than 0.1 g/cm.sup.3, a pore volume of more than 3 cm.sup.3 /g
and an adsorbency for liquids defined in terms of oleic acid of at least
2.5 cm.sup.3 /g.
According to a second aspect of the present invention there is provided a
process for preparing a porous polymeric material comprising preparing an
emulsion whose internal phase comprises 75 to 98 volume % of the material
and consists of globules having dimensions in the range 100 to 0.5 .mu.m
and forming in the continuous phase a cross-linked polycondensation
polymer.
Preferably the internal phase is removed e.g. by washing and drying, the
latter if necessary vacuum assisted.
The formation of the polycondensation polymer can occur spontaneously or
can suitably be initiated by the addition of an acid or base, as
appropriate, and/or by heating the emulsion. Polycondensation reactions
can be relatively fast. Cooling can be employed to control the reaction
rate.
In one embodiment it is therefore necessary to form the emulsion first
having its internal phase of the desired dimensions and then for example
to stir acid or base into the emulsion and, if necessary, heat.
In another embodiment when the reaction is sufficiently slow the emulsion
can be formed containing all the necessary components and the reaction
allowed to proceed, if necessary by heating.
In another embodiment the already formed emulsion containing a reactant in
the continuous phase, and if necessary an acid or base as catalyst, can be
brought into contact with the other reactant which then diffuses into the
continuous phase and interacts with the first reactant to form the
cross-linked polycondensation polymeric material. Suitably the other
reactant is dissolved in an inert solvent and the prepared emulsion is
added to or extruded in sheet like form into the solution. Alternatively
the other reactant could be in gaseous form.
Where two or more reactants are present in the ready formed emulsion they
can each be in the continuous phase, or possibly they can be split between
the two phases. In the latter case one or more reactants can be initially
dissolved in one phase and other reactant in the other phase prior to
preparing the emulsion.
Cross-linking is present in the final product either inherently due to the
number of reactive groups on the monomer or prepolymer or by the presence
of appropriate cross-linking agents, for example polycondensation
cross-linking agents.
In order to prepare the emulsion generally an emulsifier can be present,
suitably in a concentration in the range 0.1 to 25% by weight with respect
to the continuous phase. Suitable emulsifiers include amphoteric
emulsifiers such as Miranol C2M-SF and Admol Wol, Span 80, Tween 20,
sucrose esters, and mono-oleate type emulsifiers. Either in the presence
or absence of emulsifiers the emulsion having appropriate size of its
internal phase can be achieved by stirring using for example a
conventional paddle stirrer.
The reactants are suitably present in the emulsion at a concentration of 2
to 100 wt % with respect to the continuous phase. The emulsion phases can
be derived from any two immiscible materials. The only requirement is that
the phase or phases carrying the reactant materials are able to dissolve
or disperse the reactant materials in question. The continuous phase can
for example be water or an organic solvent such as for example a
hydrocarbon or a chlorocarbon. Alternatively the continuous phase can
consist of one or more of the initial reactants.
The present process can be employed to prepare the present polymeric
products. The reaction times can be nearly instantaneous from for example
the point of the addition of the catalyst or the contacting of
spontaneously reactive components. In practice a minimum reaction time of
about 5 minutes has proved practical with a maximum time being about 6
hours. In some instances somewhat longer times may be required.
Nonetheless it can be seen that the present process can lend itself to
production on a continuous or semi-continuous process. It can moreover be
adept at allowing homogeneous products to be produced in a wide variety of
shapes or sizes. The products can for example be formed in integral blocks
in moulds or in sheet, strand or granule form by extrusion. Particulate
material can be formed by granulating for example blocks of the material.
Appropriate starting materials for the present process are those described
above. Similarly the preferred process conditions are those to provide the
preferred materials mentioned above. For example process conditions
preferably include an internal phase of at least 85% by volume, more
preferably at least 90% by volume, and having globule dimensions within
the range 20 to 0.5 .mu.m, more preferably 10 to 0.5 .mu.m.
The present invention can thus provide a highly porous cross-linked
polycondensation material having cell sizes within the 100 to 0.5 .mu.m
which is made from a high internal phase emulsion.
Embodiments of the present invention will now be described by way of
example only with reference to the following Examples.
EXAMPLE 1
Resorcinol (8.3 g; 0.075 mol) and formalin (40% aq; 12.2 g; 0.15 mol
formaldehyde) were added to a polyethylene jar and heated to 30.degree. C.
to form a homogeneous solution. After cooling to room temperature an
amphoteric emulsifier, MIRANOL C2M-SF. CONC (37% aq; 2.3 g) was added. The
resulting clear solution was stirred with a paddle stirrer while
cyclohexane (180 ml) was added dropwise over a period of 30 minutes to
form a thick high internal phase emulsion. An acidic catalyst, phosphoric
acid (50% aq; 3.0 g) was then stirred into the emulsion. An opaque rigid
polymer was formed after heating at 60.degree. C. for ten minutes. The
water and cyclohexane were removed at 75.degree. C. in a vacuum oven.
The resulting porous polymeric material was tough, hydrophobic and salmon
pink in colour. Examination of the material by scanning electron
microscopy showed it to have a structure comprising a matrix of
interconnecting cells having diameters within the range 1 to 15 .mu.m. The
material had an overall porosity of 90% by volume, a density of about 0.1
gcm.sup.-3, a compressive strength of about 9.times.10.sup.5 Nm.sup.-2 and
a permeability of about 0.1 Darcys.
EXAMPLE 2
The same procedure was used as described in Example 1. 3.0 g of resorcinol
and 4.1 g of formalin were employed. The emulsifier was hexadecylpropyl
sulphobetaine (nC.sub.16 H.sub.33 N.sup.+ (CH.sub.3).sub.2
(CH.sub.2).sub.3 SO.sub.3.sup.-) (0.14 g) and the emulsion dispersed phase
was heptane (100 ml). Addition of the catalyst p-toluenesulphonic acid
(70% aq; 1.0 g) produced a rigid polymer after 3 minutes at room
temperature, and polymerization was completed by heating to 60.degree. C.
for 30 minutes. Water and heptane were removed at 75.degree. C. under
vacuum.
The resulting porous polymeric material had similar physical properties to
the product of Example 1.
EXAMPLE 3
The same procedure was used as described in Example 1. 3.0 g of resorcinol
and 7.9 g of glyoxal (40% aq) were employed. The emulsifier was MIRANOL
C2M-SF. CONC (37% aq; 1.2 g) and the emulsion dispersed phase was
petroleum ether (60 ml, 100-120 B.Pt). Addition of the catalyst,
p-toluenesulphonic acid (70% aq; 1.0 g) followed by heating to 80.degree.
C. for 2 hours produced a rigid polymer. The water and petroleum ether
were removed at 100.degree. C. under vacuum.
The material had a porosity of about 90% by volume and cell sizes falling
within the range 1 to 15 .mu.m.
EXAMPLE 4
The procedure of Example 1 was followed with the exception that
5-methylresorcinol in place of resorcinol and the basic catalyst, sodium
carbonate (20% aq; 2.0 g), in place of the acidic catalyst, phosphoric
acid, were employed. A rigid polymer formed within 20 minutes at room
temperature. Polymerization was completed by heating for 30 minutes at
60.degree. C. Water and cyclohexane were removed in a vacuum oven.
The resulting polymeric material had a porosity and other physical
characteristics similar to the product of Example 1.
EXAMPLE 5
A two stage procedure was employed to produce a urea-formaldehyde based
porous polymer. A pre-polymer syrup was prepared initially. Formalin (40%
aq; 81 g 1.0 mol), sodium acetate (0.4 g) and concentrated ammonia (S.G.
0.88; 0.8 g) were mixed to form a homogeneous solution. Urea (30 g; 0.5
mol) was then added slowly, and the mixture heated and stirred slowly to
90.degree. C. for 30 minutes. This temperature was then maintained for 2
hours during which time the solution became cloudy. 35 ml of water was
then distilled out to yield a turbid pre-polymer syrup (70% solids). The
pH of the syrup was adjusted to 7.4 with a few drops of 0.5M NaOH to
stabilize the product. In the second step this syrup (12.3 g) was mixed
with a surfactant, MIRANOL C2M-SF. CONC (37% aq; 1.4 g), and cyclohexane
(160 ml) stirred into the mixture to form a high internal phase emulsion.
Curing of the pre-polymer was then induced by stirring in ammonium
chloride (40% aq; 1.0 g) and heating for 2 hours at 50.degree. C. The
rigid polymer thus formed was dried at 75.degree. C. in a vacuum oven.
The resulting urea-formaldehyde polycondensation material had an overall
porosity of 93% by volume and, as shown by scanning electron microscope
pictures, an interconnected cellular structure in which the cells had an
average diameter of approximately 12 .mu.m. The material was prepared in
block form, but could if desired be readily granulated.
EXAMPLE 6
An alternative one stage version of Example 5 is as follows. A solution of
formalin (40%; 16.2 g; 0.20 mol), urea (6.0 g; 0.10 mol) and MIRANOL
C2M-SF. CONC (2.5 g) was prepared and solid ammonium chloride (2.0 g)
added. Cyclohexane (197 ml) was stirred in slowly to form a high internal
phase emulsion. The emulsion was heated to 50.degree. C. for 30 minutes
then left overnight at room temperature to produce a rigid polymer. The
polymer was dried as in Example 5.
The resulting material had similar properties to the product of Example 5.
EXAMPLE 7
A phenol-formaldehyde porous polymeric material was prepared in a two-stage
process, the first involving the preparation of a pre-polymer.
A mixture of formalin (40% aq; 55 ml; 0.79 mol), phenol (30 g; 0.32 mol)
and sodium hydroxide (30% aq; 1.3 ml) was refluxed for one hour, followed
by cooling to room temperature. The pH of the resulting mixture was
adjusted to pH 7.4 with a few drops of molar lactic acid and the mixture
separated into two distinct phases. Water and excess formaldehyde were
removed by rotary evaporation to leave a clear pre-polymer syrup.
A high internal phase emulsion was produced by the dropwise addition, with
stirring, of heptane (170 ml) to a mixture of pre-polymer (15 g), water (8
ml) and Miranol C2M-SF. CONC surfactant (2.6 g). Curing was brought about
by the addition of toluene-4-sulphonic acid (70%aq; 4.0 g) followed by
heating for 2 hours at 70.degree. C. Drying of the resulting material was
carried cut by heating at 100.degree. C. in a vacuum oven.
The resulting phenol formaldehyde polycondensation polymer was recovered as
an opaque solid which was hydrophobic in nature. Mechanically the material
was very tough. Assessment of the material by scanning electron microscopy
showed it to consist of an open interconnecting cellular structure in
which the cells had a diameter within the range 0.2 to 7.0 .mu.m. The
material had an overall porosity of approximately 90% by volume.
EXAMPLE 8
The procedure of Example 7 was repeated employing 3-aminophenol in place of
phenol.
3-aminophenol (6.0 g; 0.055 mol) was dissolved in a solution of sodium
hydroxide (2.4 g; 0.060 mol) in water (1.0 g). The resulting phenoxide
solution was cooled to below 10.degree. C. and then formalin (40% aq; 8.3
g; 0.11 mol) was added incrementally to form a pre-polymer syrup. In order
to prevent premature resinification the temperature was kept below
15.degree. C.
An emulsifier, Miranol C2M-SF Conc (37% aq; 2.8 g) was stirred into the
pre-polymer syrup followed by petroleum ether (180 ml; 100-120.degree. C.
B.P.) to form a high internal phase emulsion. The emulsion was heated to
80.degree. C. for an hour. The resulting polymer was porous and rigid and
had cell sizes within the range of approximately 2 to 25 .mu.m and holes
interconnecting the cells having diameters within the range of
approximately 0.05 to 6 .mu.m.
EXAMPLE 9
A polyvinyl formal porous polymer was prepared by cross-linking a polyvinyl
alcohol. Polyvinyl alcohol (9.0 g), formalin (40% aq; 14 g), water (22.3
g) and Miranol C2M-SF. CONC (2.2 g) were mixed at 90.degree. C. to form a
viscous solution. Liquid paraffin (240 mls) was added with stirring to
form a high internal phase emulsion. An acid catalyst hydrochloric acid
(10M; 6.2 g) was slowly added with stirring and the resulting mixture was
incubated at 60.degree. C. for 8 hours. The resulting porous polymer was
washed free of liquid paraffin.
The resulting porous polymer was hydrophilic and in a hydrated state was
soft in texture with elastic properties. On drying the porous polymer
showed slight homogeneous shrinkage and an increase in rigidity.
The hydrated polymer material had cell diameters within the range 5 to 20
.mu.m and an overall porosity of approximately 90% by volume.
EXAMPLE 10
A mixed polycondensation polymeric material was prepared.
The first stage of Example 7 was followed to yield a clear pre-polymer
phenol formaldehyde syrup. 20 parts by weight of this syrup were admixed
with 80 parts by weight of a polyvinyl alcohol-formalin containing viscous
solution described in Example 9. A high internal phase emulsion was
prepared from this admixture by adding with stirring liquid paraffin. Acid
catalyst, toluene-4-sulphonic acid (70% aq), was added to the emulsion
which was then allowed to cure at 80.degree. C. for 8 hours.
After extracting the liquid paraffin the resulting porous polymeric
material was tough and rigid in the dry state. The hydrated polymer had
cells of a similar size to the product of Example 9, but was somewhat
firmer and less elastic.
EXAMPLE 11
A melamine-formaldehyde based porous polymer was prepared by a two step
method similar to Example 5. Melamine (63 g; 0.5 mol) was added to
neutralised (pH 7-7.5) formalin (40% aq; 113 g; 1.5 mol). Ammonia solution
(0.880; 1.3 ml) was added and the mixture stirred and heated to boiling.
The resulting homogeneous solution was refluxed for 40 minutes, then
concentrated under reduced pressure to give a clear, viscous syrup (70%
solids). An aliquot of this syrup (12.2 g) was diluted with glycerol (2.3
g) and Miranol C2M-SF.CONC (1.5 g). Heptane (100 ml) was stirred in slowly
to form a high internal phase emulsion. Phosphoric acid (50% aq; 1.0 g)
was mixed in and the catalyzed emulsion heated at 70.degree. C. for an
hour.
The resulting polymeric material was further heated at 150.degree. C. under
vacuum to dry it and complete the cure.
The final polycondensation material was rigid and comprised an open
cellular structure. The cells had a diameter within the range 1 to 12
.mu.m. The material had an overall porosity of approximately 88% by
volume.
EXAMPLE 12
A polycondensation polymeric porous material embodying the present
invention was prepared using as a starting material a commercially
available epoxy adhesive resin. A xylen solution of the epoxy resin and
hardener containing the water-in-oil emulsifier Span 80 was prepared.
Water was stirred into the xylene solution in a ratio of water to xylene
solution of 90:10 to form a high internal phase emulsion with water as the
dispersed phase. The emulsion set to a hard rigid porous polymer in about
12 hours at room temperature. The porous polymer had an overall porosity
of about 90% by volume and interconnecting cells having diameters within
the approximate range of 1 to 30 .mu.m.
EXAMPLE 13
A polyamide based porous cross-linked polymer was prepared by injecting a
high internal phase emulsion containing a diamine into an organic phase
containing a triacid chloride. Hexamethylene diamine (2.3 g),
triethylamine (4.4 g) and Miranol C2M-SF. CONC (37% aq; 1.2 g) were mixed
together. Cyclohexane (80 ml) was stirred into this mixture to form an
emulsion. A receiving phase consisting of 1,3,5-benzenetricarboxylic acid
chloride (3.5 g) in toluene (20 ml) was prepared. The emulsion was
introduced into a glass syringe, and thence extruded into the receiving
phase. Polymer was formed when the reagents were contacted and they were
allowed to react for a further hour at room temperature. The resulting
porous polymer was washed with water and ether, and dried under vacuum.
The polyamide (nylon 6,6) material recovered was in the form of threads and
granules as a result of the extrusion approach to its preparation.
Mechanically the polycondensation material was found to be tough, but also
rather brittle. Scanning electron microscopy analysis showed the material
to have an interconnected open cell structure, with the cells having a
diameter within the range 1 to 10 .mu.m. The dried material had an overall
porosity of approximately 90% by volume.
EXAMPLE 14
The procedure of Example 13 was repeated using in place of the
hexamethylene diamine, m-phenylene diamine (2.2 g).
The resulting porous polymer had similar physical properties to those of
Example 13.
EXAMPLE 15
A silicone based porous polymer was prepared by cross-linking a linear
siloxane pre-polymer. Silicone pre-polymer B (J-SIL Silicones (UK), 11.5
g) which is a room temperature vulcanizable silicone elastomer comprising
silanol capped polysiloxane, SILESTER OS (Monsanto, 8.0 g) which is a
polymeric alkyl silicate containing the equivalent of 40% SiO.sub.2, and
two surfactants, ARLACEL 987 (a sorbitan mono-oleate having an HLB of 4.3;
1.8 g) and SPAN 85 (a sorbitan monoisostearate having an HLB of 4.3; 1.8
g), were mixed together. The catalyst dibutyl tin dilaurate (0.5 g) was
added as the last component of this phase. Water (130 ml) was stirred in
by hand to form a high internal phase emulsion over a period of 15
minutes. The emulsion was then left to cure for a further 30 minutes at
room temperature before it became rigid, while remaining flexible. After
further curing at room temperature overnight, and drying at 60.degree. C.
in a vacuum oven, a soft porous silicone based polymer was obtained.
The resulting polysiloxane, silicone based, polymer had an open cellular
structure with the constituent cells having an average diameter of about
10 .mu.m. The material was opaque, soft and flexible in nature and
exhibited a snappy elastic return. The material had an overall porosity of
approximately 80% by volume.
EXAMPLE 16
A proteinaceous porous polymer was prepared by cross-linking a
macromolecular structured polyamide bovine serum albumin.
Bovine serum albumin was dissolved in an aqueous phase at a concentration
of 30 wt:%. An oil-in-water emulsion having an internal phase of 86% by
volume was formed by the addition with stirring of light liquid paraffin
in the presence of Miranol C2M-SF. CONC (2 g per 100 ml reaction mixture).
Aliquots of the high internal phase emulsion were dialysed against 50 wt %
gluteraldehyde solution.
The resulting cross-linked polymeric material had an open cellular
structure which allowed the internal oil phase to be removed and the
material to be washed and dried. On drying a small amount of homogeneous
shrinkage occurred. The dried material was self-supporting, hard and
brittle.
Prior to drying the porous material had an overall porosity of
approximately 86% by volume and comprises interconnected cells having
diameters within the range 1 to 20 .mu.m.
Tests were performed on each of the above products to show the cross-linked
nature of the polycondensation porous materials. Each product was
subjected to a series of tests in order to assess its solubility with
respect to a range of solvents. Each test was performed by covering
approximately 50mg of the product with 3 to 5 ml of the test solvent in a
test tube and leaving overnight. The effect of the solvent on the products
after the respective time was noted. Each product was subjected to a
dissolution test in each of: water, toluene, chloroform,
dimethylformamide; concentrated (98%) sulphuric acid (H.sub.2 SO.sub.4),
acetone, and in some cases m-cresol. The toluene and m-cresol tests
involved heating in a bath held at 80.degree. C. for 6 hours.
By way of comparison equivalent tests were performed on a range of porous
polycondensation materials that were known to be not cross-linked. These
materials were prepared by the method disclosed in GB No. 1576228 (AKZO)
in which it is an essential feature of the preparative method disclosed
that the resulting polymeric materials are thermoplastic and soluble. Two
of the comparative materials tested were examples of materials obtained
commercially from AKZO and thus made by AKZO.
The comparative materials employed and produced according to the method
disclosed in GB No. 1576228 were: A. polyethylene; B. polypropylene
(commercially available sample); C. polystyrene; D. synthetic butyl rubber
(70% butadiene content); E. ethylene/acrylic acid salt copolymer (>40%
CO.sub.2 Na); F. polycarbonate (from Bisphenol A); G. polyphenylene oxide;
H. nylon 6 (commercially available sample); I. nylon 66; J. nylon 11.
The results of the tests are given in the Table below.
__________________________________________________________________________
Product
Solvent Tested
Example
Toluene
Chloroform
Water
DMF H.sub.2 SO.sub.4
Acetone
m-Cresol
__________________________________________________________________________
1 I I I I I (sw)
I --
3 I I I I (sw)
I (sw)
I --
4 I I I I I (sw)
I --
5 I I I I I (p/d)
I --
7 I I I I I I --
8 I I I I I (sw)
I --
9 I I (sw)
I (sw)
I (sw)
I (sw)
I (sw)
--
10 I I (sw)
I (sw)
I (sw)
I I --
11 I I I I I (sw)
I --
12 I (sw)
I (sw)
I I (sw)
I (sw)
I --
13 I I I I I (sw)
I I
14 I I I I I (sw)
I I
15 I (sw)
I (sw)
I I I (d)
I --
16 I I (sw)
I I (sw)
I (sw)
I --
A S -- -- -- -- -- --
B S -- -- -- -- -- --
C S S -- -- -- S --
D -- S -- -- -- -- --
E -- -- S -- -- -- --
F -- S -- S -- -- --
G S -- -- S -- -- --
H -- -- -- -- S -- S
I -- -- -- -- S -- S
J -- -- -- -- S -- S
__________________________________________________________________________
I: Insoluble
S: Soluble
sw: swollen
p: partially soluble
d: chemically degraded
As can be seen from the results tabulated above all of the products
embodying the present invention are insoluble in a range of solvents. The
very aggressive solvent concentrated sulphuric acid caused in a number of
instances chemical degradation of the materials.
By contrast the range of non-cross-linked samples were readily soluble.
* * * * *
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