Aqueous phase separation method

Abstract

The invention is in the field of methods for preparing polymer films, and of such polymer films. The method involves phase separation and requires only aqueous solution, eliminating the need for organic solvents. The aqueous phase separation involves contacting a polymer solution comprising a trigger-responsive polymer with an aqueous coagulation solution in which the trigger-responsive polymer is not soluble.

Claims

1. A method for creating a porous film through aqueous phase separation, the method comprising the steps of: I) providing an aqueous polymer solution comprising a dissolved trigger-responsive polymer wherein the trigger-responsive polymer is responsive to a change in pH, and wherein at least 80% of the solvent is water; II) contacting the aqueous polymer solution with an aqueous coagulation solution in which the trigger-responsive polymer is not soluble, and wherein at least 80% of the solvent of the aqueous coagulation solution is water, and wherein the aqueous coagulation solution has a suitable pH difference from the aqueous polymer solution to cause a transition from soluble to insoluble for the trigger-responsive polymer, allowing an entirely aqueous phase separation process; and III) allowing solvent exchange between the aqueous polymer solution and the coagulation solution to form a porous film.

2. The method according to claim 1, wherein the trigger-responsive polymer is selected from the group consisting of poly(2-diethylaminoethylmethacrylate) (PDEA), poly(N-isopropyl-acrylamide) (PNIPAM), poly(methacrylic acid)-co-(methyl methacrylate) (PMAA-co-PMMA), poly(4-vinylpyridinium) (P4VP), poly(methacrylic acid) (PMAA), poly(acrylic acid) (PAA), poly(styrene sulfonic acid) (PS S), polyaminostyrene (PAS), poly(styrene)-co-(maleic acid) (PS-co-PMA), poly(maleic acid) (PMA), poly(vinyl sulfonic acid) (PVS), sulfonated 30 polyethersulfone (sPES), sulfonated polysulfone (sPSU), poly(ethylene imine) (PEI), poly(allylamine) (PAH), elastin-like polypeptide (ELP), poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA), poly(diallyl-dimethyl-ammonium chloride) (PDADMAC), poly(oligoethylene glycol)acrylate (pOEA), poly(oligoethylene glycol)acrylamide (pOEAAm), poly(oligoethylene glycol)methacrylate (pOEMA), poly(oligoethylene glycol)acrylamide (pOEMAAm), sulphonated poly(ether ether ketone) (SPEEK), chitosan, and polysulfobetaine (PSBMA), or a copolymer thereof.

3. The method according to claim 2, wherein the trigger-responsive polymer is a polycationic polyelectrolyte or a polyanionic polyelectrolyte, wherein the polycationic polyelectrolyte is selected from the group consisting of poly(2-diethylaminoethylmethacrylate) (PDEA), poly(4-vinylpyridinium) (P4VP), polyaminostyrene (PAS), poly(ethylene imine) (PEI), poly(allylamine) (PAH), poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA), chitosan, and poly(diallyl-dimethyl-ammonium chloride) (PDADMAC), or a copolymer thereof, and wherein the polyanionic polyelectrolyte is selected from the group consisting of poly(methacrylic acid)-co-(methyl methacrylate) (PMAA-co-PMMA), poly(methacrylic acid) (PMAA), poly(acrylic acid) (PAA), poly(styrene sulfonic acid) (PSS), poly(vinyl sulfonic acid) (PVS), sulfonated polyethersulfone (sPES), sulfonated polysulfone (sPSU), poly(styrene)-co-(maleic acid) (PS-co-PMA), sulphonated poly(ether ether ketone) (SPEEK), and poly(maleic acid) (PMA), or a copolymer thereof.

4. The method according to claim 3, wherein the aqueous polymer solution comprises both a polycationic polyelectrolyte and a polyanionic polyelectrolyte.

5. The method according to claim 4, wherein the aqueous polymer solution comprises equal amounts of the polycationic polyelectrolyte and of the polyanionic polyelectrolyte, determined by monomeric ratio.

6. The method according to claim 4, wherein the aqueous polymer solution comprises an excess of the polycationic polyelectrolyte or of the polyanionic polyelectrolyte, determined by monomeric ratio.

7. The method according to claim 1, further comprising the step of: IV) crosslinking the porous film.

8. The method according to claim 7, wherein the crosslinking is via dihaloalkanes, diamines, via heating of the porous film, or via radiation.

9. The method according to claim 7, wherein the aqueous polymer solution comprises equal amounts of a polycationic polyelectrolyte and of a polyanionic polyelectrolyte, determined by monomeric ratio, and wherein the crosslinking reduces the amount of anionic groups in the polyanionic polyelectrolye, or reduces the amount of cationic groups in the polycationic polyelectrolyte.

10. The method according to claim 1, wherein the aqueous polymer solution comprises further additives, wherein the further additives are selected from the group consisting of a polypeptide, a nanoparticle, and a macromolecule.

11. The method according to claim 10, wherein the porous film is a catalytic film, wherein the further additive is an enzyme, a small molecule catalyst, a macromolecule, or a nanoparticle.

12. The method according to claim 1, wherein the porous film is an anti-viral film or anti-microbial film, wherein the aqueous polymer solution comprises further additives selected from the group consisting of anti-microbial nanoparticles, anti-microbial polypeptides, and anti-microbial macromolecules.

13. The method according to claim 1, wherein the porous film is an asymmetric porous film, wherein the method comprises the additional steps of: selecting a suitable concentration for the trigger-responsive polymer, or selecting a suitable temperature for step II), or selecting a suitable temperature for step III), or selecting a suitable coagulation solution.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1—schematic illustration of the aqueous phase separation (APS) process, in this case using a pH-based trigger to create a porous film. A) an aqueous polymer solution is applied on a surface to create a coated surface. The polymers in the coating are in solution in the low pH of the coating. B) the coated surface, which is coated with an aqueous polymer solution coating, is immersed in a coagulation bath. The bath comprises an aqueous coagulation solution in which the trigger-responsive polymer is not soluble. Equilibration of the overall pH to the value of the coagulation solution leads to phase change of the previously dissolved trigger-responsive polymer. C) based on the kinetics of the solvent exchange, the porous membrane can be symmetric (fast, near-simultaneous exchange throughout the entire coating) or asymmetric (fast exchange at one surface of the coating, slower exchange deeper within the coating).

(2) FIG. 2—schematic illustration of polymer blending and their outcomes. A) Blending two uncharged polymers often results in phase separation due to polymer incompatibility. B) For a charged and a neutral polymer, mixing is favoured as it maximizes the distance between the charged (self-repelling) polymers. C) This principle also holds when a third component with a higher or lower charge density is added, for example an enzyme. Full mixing remains the most favourable option to achieve distance between charges.

(3) FIG. 3—scanning electron micrographs of P4VP porous films. Scale bars represent 10 μm. A) 17% by weight P4VP. B) 25% by weight P4VP.

(4) FIG. 4—scanning electron micrographs of polyelectrolyte porous films based on PSS and a weak polycation (either PAH or PEI). Scale bars represent 10 μm. A) PSS and PEI; the top of the membrane is on the left of the image. B) PSS and PAH; the top of the membrane is at the top of the image.

(5) FIG. 5—pure water permeabilities of the porous films as prepared by the method according to the invention, as a function of pressure applied to the water as a driving force for transport. A) permeability for a P4VP porous film with and without crosslinking. B) permeability for a PAH/PSS based membrane crosslinked with glutaraldehyde; a non-crosslinked film was also prepared but it tore during the measurement due to a lack of mechanical stability.

EXAMPLES

Example 1

Polymer Film Comprising a Single Type of Polymer

(6) An aqueous polymer solution comprising a trigger-responsive polymer (17% by weight P4VP, pH 1) was cast on a glass surface at 200 μm thickness and immersed in a coagulation bath (pH 12). Within 40 seconds the polymeric film turned white, indicating phase separation with a resultant porous structure. SEM investigations (FIG. 3a) show a clear interconnected porous structure, symmetrical throughout the film. Repeating this experiment at a higher polymer concentration (25%, FIG. 3b) led to a similarly porous film but with smaller pores. Also, some first hints of a more asymmetric structure are observed with small pores on top and a more open structure deeper down. The membrane material itself was strong but brittle, although when it is immersed in water it swelled slightly making it more flexible.

Example 2

Polymer Film Comprising Two Polyelectrolytes

(7) The polyelectrolyte Poly(styrene sulfonic acid) (PSS, strong polyanion) was mixed with either poly(ethylene imine) (PEI) or poly(alylamine) (PAH) (both weak polycations) in a one to one monomeric ratio (20% by weight polyelectrolyte) at pH 13. At this pH, PEI and PAH are uncharged and mix easily and without complexation with the anionic PSS. A film was cast and immediately immersed in a coagulation bath at pH 2. As shown in FIG. 4, phase separation led to porous materials in both cases, albeit with different structures. The PEI/PSS film has quite open pores and cavities, but the top layer seems relatively dense. For PAH/PSS the pores are smaller and the layer is more uniform. Another porous films (not shown) was successfully prepared with the use of the polyelectrolytes poly(acrylic acid) (PAA) and poly(diallyl-dimethyl-ammonium chloride) (PDADMAC). The mechanical strength of the membrane materials varied depending on the used polyelectrolytes, from soft and flexible to hard an brittle. The materials swell somewhat in water and were found to be stable in organic solvents including THF, hexane, and acetone.

Example 3

Crosslinking of Polymer Films

(8) The pure water permeability of porous films prepared by the method according to the invention was compared for crosslinked and non-crosslinked films. As shown in FIG. 5, for a non-crosslinked porous film of P4VP a decrease in permeability as a function of applied pressure was observed. The non-crosslinked film was prepared as described in example 1. This result indicates that the porous film becomes compacted under pressure, lowering its permeability at higher pressures. For a crosslinked film crosslinked with 1,6-dibromohexane (2% (vol.) for 2 hours), however, the mechanical properties are improved and a completely stable permeability is observed, indicating a stable structure. Similar results were observed for PAH/PSS crosslinked with glutaraldehyde (0.05% (wt.) for 4 hours). For the PAH/PSS porous film the retention of a fluorescent dye (calcein, a small water soluble organic molecule of 623 g/mol) was measured and was observed to be 98%, demonstrating that these porous films can be used as membranes to retain, for example, small organic molecules. The non-crosslinked film, prepared as described in example 2, tore under the pressure applied during the comparative experiment.

REFERENCES CITED

(9) U.S. Pat. No. 2,958,682 U.S. Pat. No. 3,819,589 WO2017043233 De Grooth, J.; Oborny, R.; et al., J. Membrane Science, 2014, 475, 311. Loeb, S.; ACS Symposium Series, Vol. 153, DOI: 10.1021/bk-1981-0153.ch001 Rankin and Lowe; Macromolecules 2008, 41, 614-622; DOI: 10.1021/ma701952c Reuvers, A. J.; van den Berg, J. W. A.; Smolders, C. A. J. Membrane Science, 1987, 34, 45. Wandera, D.; Wickramasinghe, S. R.; Husson, S. M. Journal of Membrane Science, 2010, 357, 6.