Process for the preparation of porous polymer beads

Isotropic porous polymer beads having controllable surface porosity and large pore diameters from about 0.002 to about 5 microns are produced from solutions of an acrylonitrile polymer or a copolymer by a thermally-induced phase separation process including intensively shearing the polymer solution into small droplets. The use of mixed solvent non-solvent combinations as solvents for the polymers, and preferably reducing the polymer content in solution to below 10 percent produces high pore content, substantially spherical beads having a morphology ideally suited to the chromatography of large molecules, such as proteins, and for enzyme-binding.

CROSS-REFERENCE TO RELATED APPLICATION 
This application is related to a commonly assigned, concurrently filed 
application of Michael Timothy Cooke, and Laura Jean Hiscock for Porous 
Polymer Beads and Process, Ser. No. 07/275,256, and Michael Timothy Cooke 
and Laura Jean Hiscock for Porous Polyacrylonitrile Beads and Process, 
Ser. No. 07/275,317. 
This invention relates to isotropic porous polymer beads of an 
acrylonitrile having controllable surface porosity pore diameters ranging 
from 0.002 to 5 microns and a pore volume of not substantially less than 
1.5 ml/g. The beads are made from acrylonitrile polymer solutions by a 
thermally-induced phase separation process. The morphology of the beads 
makes them ideally suitable for use in chromatography applications 
especially in biomolecular separation processes such as protein 
separations. 
BACKGROUND OF THE INVENTION 
Phase separation processes of polymer solutions, including those of 
acrylonitrile, have been very useful for the preparation of porous 
low-density microcellular plastic foams, primarily in the form of fibers, 
sheets and blocks or slabs. 
In U.K. Patent Specification No. 938,694, a microporous material is made by 
mixing a finely divided thermoplastic resin with a gel-forming solvent 
therefore, raising the temperature of the mixture above the gelling point 
thereof, decreasing the temperature to form a gel and removing the gel 
forming-solvent from the mixture by treatment with a solvent for the 
gel-forming solvent but not for the thermoplastic resin In the example of 
this U.K. patent, 35 percent by volume of polyethylene resin was heated 
with 65 percent by volume of xylene at 140.degree. C. and allowed to cool 
to room temperature, whereupon a gelled mass was formed The mass was cut 
into sheets and the xylene was extracted with ethanol. After removal of 
the ethanol with water, microporous foam sheets were obtained, which had a 
pore size of below about 1.0 micron and a total porosity of about 65 
percent, the sheets being useful as separators in a storage battery, for 
example. 
In Young, et al., U.S. Patent No. 4,430,451, such a process was used to 
produce low density foams from poly(4-methyl-lpentene) resin and a solvent 
comprising bibenzyl and using, for example, methanol, to remove the 
bibenzyl leaving the resin in the form of a fragile, microcellular, low 
density foam, having a broadly disclosed pore volume of from 90 to 99 
percent, and a specifically exemplified pore volume of about 94 percent. 
Such foams were machined into blocks for laser fusion targets. 
In Castro, U.S. Patent Nos. 4,247,498 and 4,519,909, the thermally-induced 
phase separation technology was employed to make microporous foams in 
forms ranging from films to blocks to intricate shapes. In the '909 
Patent, it is stated in Col. 6, lines 34-35, that "as the solution is 
cooled to the desired shape, no mixing or other shear force is applied 
while the solution is undergoing the cooling." This strongly suggests that 
beads were not contemplated. In the '909 Patent at Col. 27-28, microporous 
polymers containing functional liquids are disclosed. The polymers are 
said to have either a cellular or non-cellular structure in which the 
liquid is incorporated. A cellular structure is defined in Col. 7 as are 
having a series of enclosed cells having substantially spherical shapes 
with pores or passageways interconnecting adjacent cells, the diameter of 
said cells being at least twice the diameter of said pores. Such a 
morphology is not ideal for adsorbing large molecules because the 
passageways are not of uniform diameter and this represents a serious 
drawback for large molecule absorption and desportion. 
Stoy, U.S. Patent No. 4,110,529, disclosed spherical polyacrylonitrile 
beads formed by a process in which a polymer solution is dispersed in a 
"liquid dispersing medium that is a nonsolvent for the polymeric material 
and and is immiscible with the solvent." The emulsion is added "with 
stirring into an excess of a coagulating liquid that coagulates the 
polymer material . . . and that is a non-solvent for the polymer material, 
is miscible with the solvent, and is immiscible with the dispersing 
medium." In adopting the classical method to making beads, applicants 
herein can, for example, form a hot emulsion of a polymer solution in 
mineral oil and quench the same by adding it to mineral oil at a lower 
temperature. Therefore, applicants do not use a "coagulating" bath which 
is immiscible with the polymer solution and miscible with the dispersing 
medium. The main drawback with the Stoy process, however, is that, even 
though up to or greater than 95 percent void content is obtained, as set 
forth in Col. 3, lines 39-41, "a non-sticky skin is formed on the surface 
of the droplets at the very beginning of the coagulation." Such a skin 
cannot be controlled by such a process and is only partially permeable, 
thus substantially interfering with the absorption and desorption of large 
molecules, and making very desirable the production of non-skinned or 
controllably skinned microporous beads. Additionally, as will be shown in 
the comparative examples hereinafter, beads made using the process 
disclosed in Stoy possess nonisotropic pores, with large pores 
concentrated in the interior and thus further contributes chromographic 
applications and the desorption of large molecules. 
Matsumoto, in U.S. Patent No. 4,486,549 generally discloses porous fibers 
and filaments, but also teaches the formation of polyacrylonitrile 
particles having a porous structure by adding the polymer solution 
dropwise into an atomizer cup in Example 1 of the patent. However, beads 
produced in this method have low pore volume, 0.90 ml/g, as seen in 
Comparative Example 1A of this application, this is responsible for low 
capacity The particles tend to be flattened and non-spherical, as shown in 
FIG. 8, and this will cause excessive pressure drops. 
Of general interest is Josefiak et al., U.S. Pat. No. 4,594,207, in which 
the technology is used to produce porous bodies, such as fibers, hollow 
filaments, tubes, tubing, rods, blocks and powdery bodies from 
polyolefins, poly (vinyl esters), polyamides, polyurethanes, and 
polycarbonates. Polyacrylonitriles were not used. There were adjustments 
in total pore volume, pore size, and pore walls made by varying solvent 
ratios; the pore volumes exemplified are in the 75-77.5 percent range. 
Josefiak discloses shaping the viscous solution by methods requiring no 
shearing during cooling. Examples 1-5 in the Josefiak patent describe the 
shaping of hollow filaments by spinning the solution through a hollow 
filament nozzle and then cooling; and Examples 5-7 describe the forming of 
membranes by coating a plate glass with the solution and then cooling. It 
is also noticed in Josefiak, U.S. Pat. No. 4,666,607, Col. 2, line 43 to 
Col. 3, line 14 that he teaches away from using strong shear forces during 
cooling. At no point in the disclosures does Josefiak contemplate the use 
of turbulence during cooling, thus, strongly suggesting that beads were 
not contemplated. In contrast to the present invention, shear is used in 
the solution prior to and during cooling, so as to form droplets which 
cool into beads These beads surprisingly provide a high degree of 
separation capability in in chromatographic applications, low resistance 
to chromatographic flow rates and excellent morphological advantages for 
column packing applications, such as having good compressive strength and 
being substantially spherical. In Zwick, Applied Polymer Symposia, No. 6, 
109-149, 1967, a similar method was used to prepare microporous fibers 
using polymer concentrations in the wetspinning range, 10-25 percent, 
producing microporous structures with pore volumes in the 75-90 percent 
range. 
In Coupek et al., U.S. Pat. No. 3,983,001, is described a method of 
isolating biologically active compounds by affinity chromatography. The 
compounds isolated include enzymes, coenzymes, enzyme inhibitors, 
antibodies, antigens, hormones, carbohydrates, lipids, peptides and 
proteins as well as nucleotides, nucleic acids and vitamins, such as 
Vitamin B. Among the porous carriers are mentioned polyacrylonitrile 
particles, but these are macroporous, require secondary shaping processes 
to form particles from the gel obtained by practicing this invention, and 
are inferior in other chromatographic processes, particularly for size 
exclusion chromotography. 
The current state of the art of microporous beads for purification, 
chromatography, enzyme binding and the like, are represented by the highly 
porous hydrophylic resins for sale under the trademark SEPABEADS.sup..RTM. 
by Mitsubishi Chemical Industries Limited. These are said to comprise 
hard spherical gel beads composed of highly porous hydrophilic vinyl 
polymer. They have an average diameter of 120 microns and a pore volume of 
less than 1.6 ml/g. Also to be mentioned, the same company produces 
DIAION.sup..RTM. highly porous polymer beads comprised of styrene 
crosslinked with divinyl benzene. Such beads can have a narrow pore size 
distribution, their pore volume is less than 1.2 ml/g. 
It is thus apparent from the state of the art set forth above that a major 
drawback of many microporous polymer structures has been the pore volume 
being less than desired, typically from 20 to 75 percent of the polymer 
structure, or up to 90 percent, but, as seen in Castro, mechanical 
strength difficulties arise. Lower void volume enhances mechanical 
strength, but produces low capacity when used in structures such as 
chromatography adsorbants. Other prior art structures are in the shape of 
fibers, filaments or membranes and cannot be effectively used to pack 
chromatographic columns, thus requiring costly secondary shaping 
equipment. Many of the prior art structures are not rigid and can swell 
with changes in ionic strength or solvent making column packing and 
control difficult. 
It has now been discovered that microporous beads, substantially spherical 
in shape, having very high void volume, a surface of controlled porosity, 
large pore diameters and high mechanical strength can be produced in 
thermal-induced phase separation methods by judicious selection of process 
techniques. Such beads are novel and their valuable properties are 
entirely unexpected in view of the prior art and the best materials made 
commercially available to date. The non-skinned beads of this invention 
permit access of large molecules to their inner surface areas. They are 
made by a process which does not involve difficult to control chemical 
reactions, such as formation of beads from monomers. The morphology of the 
beads makes them ideally suited for most chromatography applications, 
especially for the chromatography of proteins. They can also be used for 
enzyme immobilization, hormone separations, and for many other 
applications.

SUMMARY OF THE INVENTION 
In accordance with the present invention there are provided highly porous 
beads with controlled surface porosity comprising a polymer or copolymer 
of an acrylonitrile, said bead being substantially non-swellable in water, 
and having substantially uniform pores of not substantially greater than 
about 5 microns in diameter and wherein the pore volume is not 
substantially less than about 1.5 ml/g. 
The invention also contemplates such porous polymer beads, the pores being 
at least partially filled with a high molecular size compound, and the 
beads being substantially spherical. 
In a preferred manner of making the beads, acrylonitrile polymer or 
copolymer is dissolved in a solvent mixture that can only solubilize the 
polymer at elevated temperatures. The solvent mixture contains a good 
solvent for the polymer mixed with at least one additive that decreases 
the solvating power of the solvent. This additive can be a non-solvent for 
the polymer. The homogeneous liquid solution is subjected to a shearing 
process to produce droplets of the polymer solution. Preferred methods of 
shearing the two phase liquid mixture to form droplets are homogenization, 
break up of laminar jets, atomization, static mixing, and 
ultrasonification. When using homogenization or static mixing, the 
homogeneous polymer solution is suspended in a hot inert dispersing liquid 
prior to shearing. Upon cooling the suspension, a phase separation occurs 
between the polymer and polymer solvent producing droplets of said polymer 
and polymer solvent. The droplets are introduced to a cool inert liquid 
with stirring. The droplets are then collected and the polymer solvent is 
extracted to produce the porous beads of this invention. The beads have 
uniform size pores (0.002-5 microns in diameter) and no cells connecting 
the pores are seen as described in much of the prior art. The cell 
diameter to pore diameter ratio C/P would be accordingly, 1.0, 
distinguishing them from the preferred embodiments of Castro. The uniform 
microporosity is believed to be due to selecting a proper 
solvent/non-solvent composition. Use of less than about 10 percent by 
weight of polymer in the solution is preferred to provide a substantially 
skinless bead with a pore volume of greater than 90 percent. The facts 
that the beads have controllable surface porosity that they do not stick 
together and that they possess good handling strength even at high pore 
volume are entirely unexpected. 
DETAILED DESCRIPTION OF THE INVENTION 
The porous beads of this invention are made from acrylonitrile polymers 
and/or copolymers. The acrylonitrile copolymers comprise polyacrylonitrile 
copolymerized with a (C.sub.2 -C.sub.6) mono-olefin, a vinylaromatic, a 
vinylamino aromatic, a vinyl halide, a (C.sub.1 
-C.sub.6)alkyl(meth)acrylate a (meth) acrylamide, a vinyl pyrrolidone, a 
vinylpyridine, a (C.sub.1 -C.sub.6) hydroxyalkyl(meth)acrylate, a 
(meth)acrylic acid, a (C.sub.1 -C.sub.6) alkyl (meth)acrylamide, an 
acrylamidomethylpropylsulfonic acid, an N-hydroxy-containing (C.sub.1 
-C.sub.6)alkyl (meth)acrylamide, or a mixture of any of the foregoing. 
As solvents for acrylonitrile polymers, any organic or inorganic liquid 
capable of dissolving them without permanent chemical transformation can 
be used. These include dimethyl sulfoxide, dimethyl formamide dimethyl 
sulfone, aqueous solutions of zinc chloride and sodium thiocyanate. 
Non-solvents can comprise any liquid medium which is immiscible with the 
polyacrylonitrile or copolymers. Non-solvents can comprise urea, water, 
glycerin, propylene glycol, ethylene glycol or mixtures thereof. 
Non-solvent dispersants can comprise any liquid medium which is immiscible 
with the acrylonitrile polymers or copolymers and the polymer solvent. 
Usually, they will comprise liquids of low polarity, such as aliphatic, 
aromatic or hydroaromatic hydrocarbons and their halogenated derivatives, 
low molecular weight polysiloxanes, olefins, ethers and similar such 
compounds. 
Preferred solvent-nonsolvent systems comprise a solvent mixture of dimethyl 
sulfone-urea-water or dimethyl sulfoxide or dimethylsulfone with water, 
ethylene glycol, or propylene glycol added and the hot inert liquids of 
choice are aliphatic, aromatic, or hydroaromatic hydrocarbons such as 
mineral oil, low odor petroleum solvents, or kerosene. As extraction 
solvents, preferred are lower alkanols, such as methanol, ethanol, or 
lower ketones, such as acetone, and water. 
Control of the external porosity and pore size distribution are both 
functions of the composition of the solution of polymer, solvent and 
non-solvent(s). The ability to control porosity and pore size by these 
parameters can bee seen from FIGS. 9, 10, 11, 12, 13, 14, 15, and 16. 
Table A, below, sets forth the ratios of raw materials used to prepare the 
homogeneous polymer solution use in the preparation of these beads. 
TABLE A 
______________________________________ 
PORE CONTROL 
DIMETHYL* POLYACRY- 
FIG. WATER* UREA* SULFONE LONITRILE* 
______________________________________ 
9 3 0 24 1 
10 3 0 24 1 
11 6 0 24 2 
12 6 0 24 2 
13 1 2 24 3 
14 1 2 24 3 
15 1 6 24 1 
16 3 6 24 1 
______________________________________ 
*Units are in parts by weight. 
The polymer concentration has a greater effect on the external porosity of 
the bead than on the interior, as shown in FIGS. 9, 19, 11, 12, 13 and 14. 
This allows flexibility for preparing morphologies useful for slow-release 
applications, where the rate of release can be controlled by the extent of 
bead "skin" while maintaining internal porosity. FIGS. 9 and 13 show how 
much control over the external porosity is available while maintaining 
uniform internal porosity. This is unexpected in light of prior art, 
wherein polymer concentration is claimed to change morphology throughout 
the structure. See W. C. Hiatt, et al. Materials Science of Synthetic 
Membranes, ACS Symposium Series 269, 1985, pp. 230-244, see pp. 239-243, 
type III and type IV membranes from PVDF. The morphology of the present 
invention is also very difficult to obtain by conventional solvent phase 
separation techniques. In those cases, the solvent diffusion either causes 
asymmetric morphologies to be formed or much smaller pores. See U.S. 
4,486,549, Example 1, wherein porous polyacrylonitrile particles formed 
from an atomizer cup and quenched in aqueous dimethyl formamide using a 
solvent phase inversion process, gave low pore volumes and non-spherical 
particles. 
The overall size of the pores can be controlled by choice of the proper 
non-solvent. Pore size is also effected by both the phase separation 
temperature of the system and solidification temperature of its 
components. A larger gap between the phase separation temperature and 
solidification temperature tends to produce beads having larger pores. 
In a convenient way of proceeding, a poly acrylonitrile copolymer (98/2 
acrylonitrile/methyl acrylate by weight) is dissolved in a hot 
(110.degree.-140.degree. C.) solvent/non-solvent mixture designed so that 
the copolymer is soluble only at elevated temperatures (50.degree. to 
110.degree. C.). The composition of the mixture required to meet this 
condition is determined by running cloud point experiments to determine 
the temperature where phase separation occurs. Preferably, the solvent 
will be either dimethylsulfoxide or dimethylsulfone and the non-solvent 
will be chosen from water, urea, glycerin, ethylene glycol, propylene 
glycol, or a combination thereof. Typical total solvent/non-solvent ratios 
will vary from 95/5 to 65/35 by weight. Polymer concentrations will range 
from 0.5 to less than 20 percent total polymer solids in the 
solvent/non-solvent solution with 0.5 to about 10 percent on the same 
basis being preferred. 
The hot polymer solution is dispersed with stirring in a liquid e.g., 
mineral oil, which is substantially immiscible with the solution. 
Typically 1 volume of polymer solution is dispersed in 4 volumes of the 
liquid. The dispersion is then pumped through a static mixer (such as the 
mixer manufactured by Kenics) at a rate sufficient to form small droplets. 
The droplet size distribution can be controlled by the rate of flow 
through the static mixer. Typical diameters of the droplets range from 20 
microns to 400 microns. After the droplets exit the static mixer they are 
diluted with additional cool mineral oil, typically 4 volumes, to cool the 
droplets below the phase separation temperature. The polymer phase 
separates from the solvent/non-solvent solution and then precipitates as 
droplets of solid polymer and solvent. The solid droplets are then removed 
from the mineral oil. 
Other methods for forming small droplets of polymer solution in the 
dispersion include the use of a homogenizer, laminar jets, atomization 
nozzle, and an ultrasonic mixer. It is essential to the practice of this 
invention that the dispersion be subjected to a high shear process, thus 
ensuring the formation of substantially spherical droplets of uniform size 
and thereby precluding the need for secondary shaping as required by much 
of the prior art processes for use of their products in chromatographic 
separation processes. 
The collected droplets are then extracted with a material which is miscible 
with the solvent/non-solvent mixture but not a solvent for 
polyacrylonitrile to produce porous beads. Acetone or water can be used. 
The extracted beads are dried to produce a micro-porous product. The pore 
size of the bead can be varied from 0.002 micron to 5 microns by varying 
the polymer or copolymer composition or the concentration and type of 
non-solvent used. The total pore volume is determined by the original 
concentration of the polymer or copolymer in the solvent/non-solvent 
solution. It is also contemplated by this invention to remove the solvent 
material from the solidified beads by any convenient method such as in the 
case of liquid solvent usage, by simple washing. 
Specific applications of this technique will be exemplified in detail 
hereinafter. 
When used herein and in the appended claims, the term "pore volume" means 
milliliters of void per gram of polyacrylonitrile. Pore volume is directly 
a function of the polymer concentration. Beads with pore volume greater 
than 1.5 ml/g are especially preferred. Pore volume is measured by 
conventional means, such as mercury porosimetry. 
The term "substantially non-swellable in water" means that in water, volume 
will increase through swelling by less than 5 percent. Non-swellable beads 
are preferred since the bulk volume remains essentially constant in column 
chromatographic applications thus resulting in consistent flow rates and 
negligible head pressure losses. The term "skinless" is intended to define 
porous particles which do not exhibit a surface skin and thereby are 
efficient for direct absorption of high molecular weight molecules. Bulk 
density of the polymer beads is measured in conventional ways, e.g., by 
tapping to constant volume. The beads of this invention will preferably 
have a bulk density of greater than about 5 ml/g. Lower bulk densities are 
not as desirable because they tend to have lower capacities. The upper 
limit of bulk density is about 15 ml/g. At levels above this no economic 
advantages are noted and mechanical strength is reduced. The average bead 
diameter can vary widely, depending on its use. Preferably it will be from 
about 5 microns to about 2 millimeters, more preferably from about 5 
microns to about 150 microns. Special mention is made of bead diameters of 
about 5 microns; these are uniquely suitable for analytical high pressure 
liquid chromatography. For other chromatography uses, in general, bead 
sizes of from about 5 to about 150 microns are preferred, especially from 
5 to 20 microns, and especially preferably from 20 to 100 microns. Bead 
sizes can be measured in conventional ways, for example, by use of a 
particle size analyzer. Although the pore sizes can vary widely, and are 
measured in conventional ways, for example by nitrogen adsorption or 
mercury intrusion, it is preferred that the average pore diameter be from 
about 0.002 to about 5 microns and, especially preferably, from about 0.1 
to about 1 microns. Also preferable are beads with an average pore 
diameter from about 0.002 to about 0.1 microns. When the beads are used to 
contain a compound, it is preferred that the compound comprise a protein, 
an enzyme, a hormone, a peptide, a nucleic acid, a polysaccharide, a dye, 
a pigment, or a mixture of any of the foregoing. Especially preferred for 
this are proteins. The beads may be filled with such a compound by any 
convenient means, for example, by physical entrapment, physical adsorption 
or chemical bonding depending on the compound. In any event, the porous 
beads used preferably will have pore diameters of at least about 3 times 
the diameter of the compound. 
Conventional techniques are employed to utilize the adsorptive capacity of 
the porous beads of this invention. The beads can be used, for example, to 
adsorb vitamins, antibiotics, enzymes, steroids and other bioactive 
substances from fermentation solutions. They can be used to decolorize 
various sugar solutions. They can be used to decolorize saccharified wood 
solutions. They can be used as column packing for gas chromatography, size 
exclusion chromatography, affinity chromatography, ion exchange 
chromatography, reverse phase of hydrophobic interaction applications. 
They are useful to remove phenol, and to remove various surface active 
agents. They can adsorb a variety of perfumes. They can decolorize waste 
effluents in paper pulp production, they decolorize and purify a variety 
of chemicals. The beads are also especially useful for slow release 
applications when they are made under such conditions as to cause partial 
skins on their surface. 
The beads of this invention are especially useful for protein separation. 
Proteins especially suitable for purification using the beads of this 
invention are alpha-lactoalbumin, albumin, gammaglobulin, albumin 
interferon, and the like. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The following examples illustrate the present invention. The claims are not 
to be construed as being limited thereto. 
COMATIVE EXAMPLE 1A 
Five grams of a wet copolymer containing 99 mole percent acrylonitrile and 
1 mole percent of methyl acrylate (1:1 copolymer:water by weight) were 
ground with 5 grams of urea and 30 grams of dimethylsulfone to form a 
powdered mixture. The mixture was placed in a 1 liter flask with 100 ml of 
mineral oil heated to 160.degree. C. The mixture was stirred until two 
liquid phases were present, one phase being a homogeneous polymer 
solution, the other mineral. Rapid stirring of the mixture with an 
overhead paddle stirrer gave a suspension consisting of droplets of the 
hot (about 120.degree. C.) polymer solution in mineral oil. The droplets 
were cooled by transferring the suspension via a canula to a second 
stirred mixture consisting of 500 ml of mineral oil, 6 grams of 
dimethylsulfone, and 1 grame of urea kept at 70.degree. C. The droplets 
solidified upon contacting the cooler mineral oil. The mixture was cooled 
with stirring to room temperature, then diluted with methylene chloride to 
reduce the viscosity of the oil. The droplets were collected on a Buchner 
funnel and washed with methylene chloride, then the solvent was extracted 
with 200 ml of acetone for 1.5 hours at room temperature. The resulting 
beads were examined by scanning electron microscopy and were seen to be 
highly porous, with relatively uniform pore diameters of about 0.5 
microns. The pores extended through the outer surfaces of the beads. The 
beads made by this process without high shear ranged in size from 10 
microns to a few millimeters. A SEM photograph of a cross-section of these 
beads appears as FIG. 2. 
COMATIVE EXAMPLE 1B 
Particles are made by the procedure taught in EXAMPLE 1 of Matsumoto, U.S. 
4,486,549. 120 Grams of polyacrylonitrile homopolymer is dissolved in 1800 
ml of dimethylformamide and the resultant solution is added dropwise by a 
rotational atomizer cup model PPH 306 00D (supplied by Sames Electrostatic 
Inc.) at a rate of 20 ml per minute into a 20% aqueous dimethylformamide 
solution whereby there were obtained particles of polacrylonitrile. 
An SEM photograph (FIG. 8) shows a different shape and morphology than 
obtained with the processes of the examples herein. 
COMATIVE EXAMPLES 1C AND 1D 
Beads were prepared following the teachings of Stoy, U.S. 4,110,529. 
Following the general procedure of Example 1 of the Stoy, 
polyacrylonitrile was dissolved in dimethyl sulfoxide, dispersed in 
paraffin oil, and poured in a thin stream into water at 15.degree. C. The 
procedure was repeated following Example 2 of Stoy (pouring the emulsion 
into water at 60.degree. C.). The spherical porous beads were separated 
and photographed with a scanning electron microscope. The photographs 
appear as FIGS. 5 and 6. The beads are seen to have a porous exterior and 
extremely large interconnected pores in the interior, unlike those of the 
present invention in which the beads were substantially isotropic. 
EXAMPLE 1 
Ten grams of dry copolymer consisting of 99 mole percent acrylonitrile and 
1 mole percent of methyl acrylate were ground with 10 grams of 
dimethylsulfone with a mortar and pestle. The mixture was then stirred and 
heated to 125.degree. C. to form a homogeneous polymer solution. Mineral 
oil, 600 ml, at 140.degree. C. was stirred using a Ross homogenizer, model 
LABME at a setting of 3. The hot polymer solution was slowly added to the 
mineral oil. Five minutes after all of the polymer solution was added, the 
suspension was diluted with a hot (140.degree. C.) mixture of 1800 ml of 
mineral oil, 24 grams of dimethylsulfone, and 4 grams of urea. After the 
mixture was uniformly homogeneous, the heat was removed and the flask 
placed in an ice water bath. When the suspension reached 110.degree. C., 
the homogenizer was turned off and the droplets were allowed to settle. 
After cooling the mixture to room temperature, methylene chloride was added 
to dilute the mineral oil, then the droplets were collected on a Buchner 
funnel. The droplets were washed with methylene chloride, then extracted 
with 600 ml of acetone at room temperature for 16 hours. The resulting 
beads were again collected, washed with methanol, then dried at room 
temperature under vacuum. The beads were examined by scanning electron 
microscopy. The majority of the beads ranged from 100-400 microns in 
diameter, with pore diameters of about 1 micron. The beads were skinless, 
surface porosity being as high as the interior porosity. Smaller beads 
(less than 200 microns) can be obtained by increasing the setting to 5 on 
the Ross homogenizer. 
EXAMPLE 2 
One gram of dry copolymer consisting of 99 mole percent acrylonitrile and 1 
mole percent methyl acrylate was ground with a mortar and pestle with 1 
gram of deionized water, 2 grams of urea, and 12 grams of dimethylsulfone. 
The mixture was heated to 125.degree. C. to form a homogeneous polymer 
solution. Hot mineral oil (60 ml, 150.degree. C.) was agitated in a 
Branson Sonifier Model S75 at setting 7 (tuned to 4 amps). The hot polymer 
solution was slowly added, which increased the current to 6 amps. The 
suspension was mixed for a few minutes, then diluted with 180 ml of 
mineral oil (120.degree. C.) containing 2.4 grams of dimethylsulfone and 
0.4 grams of urea. The flask was placed in a water bath to cool the 
suspension. When the suspension reached 110.degree. C. the Sonifier was 
turned off. After cooling to room temperature, the oil was diluted with 
methylene chloride and the droplets are collected on a Buchner funnel, 
then washed with methylene chloride. The droplets were extracted with 60 
ml of acetone for 16 hours at room temperature, then again collected, but 
this time washed with methanol. The resulting beads were dried at room 
temperature under vacuum. The beads were examined by scanning electron 
microscopy and were found have high pore volume, pore diameters about 1 
micron, and high surface porosity. The average bead diameter was about 50 
microns. 
EXAMPLE 3 
One hundred forty four grams of dimethylsulfone and 12 grams of urea were 
combined with 720 ml of mineral oil and heated to 130.degree. C. in a 
one-liter resin flask equipped with a stirrer, thermometer and dip leg. 
After the sulfone and urea melted, 6 grams of dry copolymer consisting of 
99:1 mole ratio acrylonitrile: methyl acrylate and 18 grams of water were 
added and dissolved to form a homogeneous solution of polymer, 
dimethylsulfone, urea and water dispersed in mineral oil. The dispersion 
was then pumped at the dip leg and through a hot 140.degree. C., 
Kenics.sup..RTM. static mixer (0.25 in. i.d., 6 in. length) at a rate 
sufficient to form droplets of polymer solution dispersed in mineral oil. 
The exit of the static mixer was placed three inches above a stirred 
quench bath of four liters of room temperature mineral oil in which the 
droplets solidified. The droplets were collected and washed with a low 
boiling hydrocarbon to remove the mineral oil and dried. Dimethylsulfone 
was extracted from the droplets by placing them overnight in either 900 ml 
of acetone or 900 ml of methanol. More preferably, the dimethylsulfone may 
be extracted by stirring the droplets in one liter of hot, 
80.degree.-95.degree. C., water for one hour. The stirrer cannot be 
allowed to contact the vessel walls or grinding of the droplets may occur. 
Beads formed in this manner were skinless, with pore diameters ranging 
from 0.1 to 1.5 microns with the majority of beads ranging from 25 to 425 
microns. 
EXAMPLE 4 
The procedure of Example 3 was repeated using 3 percent of a 99 mole 
percent acrylonitrile--1 percent methyl acrylate copolymer, and 11 percent 
water as a non-solvent. Skinless microporous polymer beads in accordance 
with this invention were obtained, as illustrated in FIG. 1. 
EXAMPLE 5 
The thermal phase separation technique of Example 3 can be repeated with 
polyacrylonitrile copolymers containing from 50 to 98 mole percent of 
acrylonitrile and using dimethyl sulfoxide, dimethyl sulfone, water, urea, 
ethylene glycol, glycerine, and propylene glycol as solvent mixture 
components to produce microporous beads in accordance with this invention. 
EXAMPLE 6 
The microporous beads of Example 4 (FIG. 1) are packed into chromatographic 
column. A buffered aqueous solution of albumin is passed through the 
column. Protein is adsorbed in the microporous beads. There is then passed 
through the column a desorbent comprising a buffered aqueous salt 
solution. A large part of the protein is recovered in a purified, 
undenatured state. 
EXAMPLES 7-8 
The procedure of Example 6 is repeated, substituting buffered aqueous 
solutions of alpha-lactoalbumin and gamma-globulin for the albumin. The 
beads take up the respective proteins from solution, and they can be 
displaced in an undenatured state by desorption with buffered aqueous 
solutions having a higher salt concentration. 
EXAMPLE 9 
A mixture of 3 parts of 99:1 mole ratio acrylonitrile: methyl acrylate, 25 
parts propylene glycol and 72 parts dimethylsulfone was heated to 
130.degree. C. to form a homogeneous solution. The solution was charged to 
a Parr reactor equipped with a magnetically driven stirrer and dip leg. 
The reactor was heated to 150.degree. C. and then the solution was forced 
through heated, 140.degree. C., lines into a heated ultra-sonic horn using 
pressurized, 35 psig, nitrogen. The flow was kept at a constant rate of 32 
ml/min. The ultrasonic nozzle operated at 35 kHz and was tuned at 
150.degree. C. (nozzle and power supply obtained from Sono-tek Corp.). The 
energy input on the nozzle was 22 watts. The liquid droplets were quenched 
in a mineral oil bath located three inches below the ultra-sonic horn. The 
oil was decanted and the solidified droplets washed with heptane and 
dried. The dimethylsulfone was extracted with hot water to provide 
microporous beads of from about 50 to 1000 micron in diameter. 
EXAMPLE 10 
Two hundred eighty-eight grams of dimethylsulfone, 12 grams of 
polyacrylonitrile copolymer consisting of 99:1 mole ratio acrylonitrile: 
methyl acrylate, and 100 ml of propylene glycol were combined and placed 
in a Parr reactor equipped with a magnetically driven stirrer and dip leg. 
The reactor was heated to 140.degree. C. to form a homogeneous solution. 
The solution was forced through heated, 140.degree. C., lines and an 
atomization nozzle (for example, Lechler Co. full cone "center jet" 
nozzle, 0.46 in. diameter orifice). using 150 psig nitrogen pressure. The 
nozzle was mounted 3 inches over 3 liters of stirred mineral oil or 4 
inches over 4 liters of stirred heptane to quench the liquid droplets. The 
solidified droplets were washed with heptane to remove mineral oil, dried 
and extracted for one hour with 3 liters of 85.degree.-90.degree. C. water 
to produce microporous beads. Pore sizes ranged from 0.5 to 1.5 microns 
with the majority of the beads between 25 and 150 microns. 
EXAMPLE 11 
A mixture of 6 grams of copolymer comprising 99:1 mole ratio acrylonitrile: 
methylacrylate, 54 grams propylene glycol and 140 grams dimethylsulfone 
was heated to 130.degree. C. to form a homogeneous solution. The solution 
was charged to a 500 ml Parr reactor equipped with a magnetically driven 
stirrer and dip leg. The solution was heated to 150.degree. C. and forced 
through heated, 150.degree. C., lines and out a heated, 150.degree. C., 
nozzle which consisted of seventy-five 50 micron diameter holes using 20 
psig nitrogen pressure. The solution was forced at a constant flow rate of 
75 ml/min. The laminar jets broke into liquid droplets which were quenched 
in a 750 ml heptane bath located 3-4 inches below the nozzle. The 
solidified droplets were collected and dried. The dimethylsufone was 
extracted with hot water to produce microporous beads with 80 percent of 
their volume ranging in size from 70 to 200 microns. 
EXAMPLE 12 
The procedure of Example 11 is followed except that the flow rate was kept 
at 30 ml/min and the solution vibrationally excited at the natural 
resonance frequency of the jet velocity (as per J. G. Wissema, G. A. 
Davies, Canadian Journal of Chemical Engineering, Volume 47, pp. 530-535 
(1969)) to form uniformly sized liquid droplets. 
The above-mentioned patents and publications are incorporated herein by 
reference. 
Many variations will suggest themselves to those skilled in this art in 
light of the above, detailed description. For example, glucose and sucrose 
solutions can be decolorized by contact with the microporous beads of this 
invention; fatty acids such as butanoic acid, propionic acid and acetic 
acid can be adsorbed from aqueous solutions with them. Soaps and 
detergents can be adsorbed from solutions using them. Enzymes can be 
adsorbed in them and then used to catalyze reactions in substrates such as 
fermentation broths passed through the beads containing such bound 
enzymes. All such obvious variations are within the full intended scope of 
the appended claims. 
EXAMPLE 13 
The procedure of Example 3 was repeated substituting 3 percent of a 99 mole 
percent acrylonitrile-1 mole percent methyl acrylate copolymer and 4 
percent of water and 13 percent of urea. Microporous beads in accordance 
with this invention were obtained, a typical cross-section of the beads 
being illustrated at 1,440.times. magnification in FIG. 3.