WO2024253581A1 - A polymer, a method of making the polymer and uses thereof - Google Patents

Abstract

The present disclosure relates to a brush-like polymer having a network of polymeric units, where each polymeric unit comprises a polymerized backbone with a plurality of hydrophilic polymeric side chains, a plurality of amphipathic polymeric side chains, and at least one amphipathic polymeric crosslinking side chain that extends from the polymerized backbone of one polymeric unit to crosslink with the polymerized backbone of an adjacent polymeric unit. The present disclosure relates to a method of preparing a brush-like polymer as defined herein, a method of forming a layer comprising a brush-like polymer as defined herein on an article, a layer comprising a brush-like polymer as defined herein, an article coated with a layer comprising a brush-like polymer as defined herein, method of using an article and use of an article thereof. In a preferred embodiment, the brush-like polymer is prepared by polymerizing acryloxy-terminated ethyleneoxide dimethylsiloxane-ethyleneoxide ABA block copolymer (PEODMS) and polyethylene glycol) methyl ether methacrylate (PEGMEMA).

Description

A POLYMER, A METHOD OF MAKING THE POLYMER AND USES THEREOF

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Singapore application number 10202301586R filed with the Intellectual Property Office of Singapore on 5 June 2023, the contents of which is hereby incorporated by reference in its entirety for all purposes.

TECHNICAL FIELD

The present invention relates to a brush-like polymer as defined herein. The present invention also relates to a method of preparing a brush-like polymer as defined herein, a method of forming a layer comprising a brush-likc polymer as defined herein on an article, a layer comprising a brush-like polymer as defined herein, an article coated with the layer comprising a brush-like polymer as defined herein, method of using the article and use of the article thereof.

BACKGROUND ART

Fossil fuel remains the greatest source to generate electricity worldwide. The combustion of fossil fuel with air in power plants emits flue gas consisting mainly of carbon dioxide (CO₂), water, and nitrogen. While both water and nitrogen arc benign to the environment, the increase of CO₂ concentration has been associated with climate change that culminated in unprecedented natural disasters globally. Reducing CO₂ generation is impractical considering the growth of global population that continuously demands higher energy consumption. Therefore, it is critical to capture CO₂ to mitigate any further unwanted effect from climate change, which can be effectively done through flue gas post-combustion carbon capture.

Since the commercialization of membranes in the early 1980s, membrane gas separation processes have rapidly grown as a competitive separation technology with advantages such as high energy efficiency, low footprint, and simple processes. However, post-combustion carbon capture by membrane remains a great challenge. For example, the typical exhaust pressure of these flue gas is relatively low (less than 1 barg). Therefore, to be commercially attractive, the membranes -p cked modules need to produce high flux. The first commercial membrane developed specifically for CO₂ capture is called Polaris ^1M. Computational studies using novel multi-stage membrane processes for power plant post-combustion CO₂ capture demonstrated the potential capture cost of less than $30 per metric ton of CO₂, which is below the target set by the US Department of Energy. Using the Polaris™ membranes packed into spiral-wound modules (flat sheet geometry), the total cost of the process was estimated to be about $23/ton of CO₂ using approximately 1.3 MM m² of membrane surface area to process the average-sized coal-fired power plant ~ 600 MWe. It has previously been estimated that approximately 50,000 spiral-wound modules (20.3 cm inner diameter, 100 cm long, 600 m²/m³) will be required to achieve this size of membrane process for each power plant. To lower the footprint, membranes can also be fabricated in hollow fibre configuration with much higher surface area-to-volume ratios approaching 10,000 m²/m³, which increases the module productivity per unit volume by more than an order of magnitude. Minimizing the footprint of the modules can further reduce the cost of carbon capture, which has become the most important factors in determining the feasibility of membrane processes in flue gas carbon capture.

Another strategy to further improve the flux of the modules is to increase the permeation rate through the membrane itself, which can be achieved by developing a highly permeable material or reducing the thickness of the membrane. While many advanced materials (e.g. zeolites, metal organic frameworks, carbon molecular sieves, graphene oxides) have been explored in the lab-bench scale showing great CO₂ permeability and perm selectivity, they tend to suffer in reproducibility and processability, and thus impractical for commercialization. Commonly available polymeric material is still the first pick for industrial membrane separation because of its affordability, ease of handling, and fabrication. However, the performance of polymeric membrane is known to be limited by the trade-off effect between its permeability and selectivity. Therefore, to improve the permeance of these sufficiently high selectivity but relatively low permeability polymeric membrane materials, they need to be fabricated into a very thin film (< 100 nm). To achieve this, many have adopted a thin-film composite (TFC) design consisting of a multilayer structure such as a substrate, a gutter, a selective, and a protective layer, respectively. In short, the substrate layer acts as the mechanical support; the gutter layer prevents the penetration of selective layer during the coating process; the selective layer is for the main separation; and the protective layer seals any defects and protects the selective layer.

Polymers containing ethylene oxide groups have been extensively investigated for the CO₂/N₂ separation as a selective layer. The ethylene oxide units interact with the CO₂ molecules through the dipole-quadrupole forces, which provides the high CO₂/N₂ solubility selectivity. One way to form a very thin cthylcnc-oxidc based polymer film is to dilute the coating concentration for the TFC fabrication. However, too diluted concentration can lead to penetration of coating solution on the subsequent substrate layer forming a defective and non- uniform film. A gutter layer was introduced as an intermediate between the substrate and selective layer to act as a foundation and prevent the coating penetration. As the selectivity performance of TFC does not rely on the gutter layer, it can be made of low selective but highly permeable material, such as polydimethylsiloxane (PDMS). PDMS has become the most commonly used gutter layer material to date because of its cheap cost, good stability, workability, and strong adhesion to many conventional membrane supports (e.g. polysulfone, polyacrylonitrile, cellulose acetate, etc.). However, one main issue arising from the use of PDMS is the low surface energy of PDMS, making it difficult to coat additional layers on top of the gutter layer. Furthermore, its strong hydrophobicity exhibits poor compatibility with the hydrophilic ethylene-oxide based materials, leading to ineffective formation of ultrathin selective layer on the PDMS gutter layer.

Researchers have reported various strategies to improve hydrophilicity, liquid affinity, and surface free energy of PDMS layer by plasma pre-treatment, grafting hydrophilic dendrimer on the surface, coating an additional polydopamine layer, and introducing bifunctional aminosilane. However, these modifications add an additional time-consuming and complex step to the fabrication of TFC. Furthermore, coating or grafting additional layers or functional groups can reduce the permeability performance of the TFC. Plasma pre-treatment forming SiOx layer can also act as strong gas barrier that leads to permeability drop as well. Additionally, the effect brought by air plasma-induced surface hydrophilicity is not permanent and will change according to storage condition and time. Thus, the selective layer needs to be coated immediately on the plasma treated PDMS, which may not be practical to be adopted for commercial processes.

Therefore, there is a need to develop a layer that can be used as a selective layer that can overcome, or at least ameliorates the disadvantages described above.

There is also a need to provide a method for forming the layer that can overcome, or at least ameliorates the disadvantages described above. SUMMARY

In one aspect, there is provided a brush-like polymer having a network of polymeric units, where each polymeric unit comprises a polymerized backbone with a plurality of hydrophilic polymeric side chains, a plurality of amphipathic polymeric side chains, and at least one amphipathic polymeric crosslinking side chain that extends from the polymerized backbone of one polymeric unit to crosslink with the polymerized backbone of an adjacent polymeric unit.

The polymeric side chains (such as the hydrophilic polymeric side chains and/or the amphipathic polymeric side chains) may be termed as the brushes. Advantageously, the “brushlike” structure allows the brush-like polymer to have high mobility, allowing the hydrophobic functional groups in the amphipathic polymeric (crosslinking) side chains to interact easily with other hydrophobic functional groups (eg. hydrophobic layer like gutter layer externally to the brush-like polymer) and the hydrophilic functional groups to interact with other hydrophilic groups (such as polar gas molecules in the external environment).

In another aspect, there is provided a method of preparing a brush-like polymer as defined herein comprising: a) dissolving at least one homopolymer comprising at least one hydrophilic polymeric side chain and at least one amphipathic co-polymer in a solvent to form a mixture; b) adding an initiator to the mixture formed in step a) to form a solution; c) polymerizing the solution formed in step b) at an elevated temperature for a duration of time to form the brushlike polymer.

As the method of preparing the brush-like polymer involves thermal polymerization, the initiator used in the reaction allows the generation of radicals which is essential for formation of the “brush-like” structure and therefore, the method as described will not lead to the formation of a non-brush structure. The polymerization as defined herein may result in the formation of a brush-like polymer having a network of polymeric units, where each polymeric unit comprises a polymerized backbone with a plurality of hydrophilic polymeric side chains, a plurality of amphipathic polymeric side chains, and at least one amphipathic polymeric crosslinking side chain that extends from the polymerized backbone of one polymeric unit to crosslink with the polymerized backbone of an adjacent polymeric unit.

In another aspect, there is provided a brush-like polymer obtained from or obtainable from a method as defined herein. In another aspect, there is provided a method of forming a layer comprising a brush-like polymer as defined herein on an article comprising: a) dissolving the brush-like polymer in a solvent to form a brush-like polymer coating solution; b) dipping the article into the brush-like polymer coating solution formed in step a) for a duration of time to form the layer on the article; and c) removing the layered article from the brush-like polymer coating solution.

In another aspect, there is provided a layer comprising a brush-like polymer as defined herein.

Advantageously, the hydrophobic groups on the amphipathic polymeric side chains can interact with the hydrophobic surface of the article that the layer is being coated on, which allows a uniform and ultrathin coating of the layer on top of the hydrophobic surface of the article. Where the layer is a selective layer in, for example, a hollow fiber membrane, the selective layer can form a uniform and ultrathin coating on top of a gutter layer, resulting in high permeance of gas when the hollow fiber membrane is used in gas separation. Furthermore, the hydrophilic polymeric side chains can interact with the gas molecules to provide high gas solubility selectivity. The selective layer can be used as part of a multilayer thin-film composite (TFC) design in membrane gas separation of gas molecules such as CO₂ or N₂, leading to high energy efficiency, low footprint, and ease of simplicity.

In another aspect, there is provided an article coated with a layer comprising a brush-like polymer as defined herein.

In another aspect, there is provided a method of using an article coated with a layer comprising a brush-like polymer as defined herein, the method comprising passing a mixture for separation across the article.

In another aspect, there is provided use of an article coated with a layer comprising a brushlike polymer as defined herein for separation.

DEFINITIONS

The following words and terms used herein shall have the meaning indicated:

The term “selective layer” as defined herein refers to a polymer layer having a suitable degree of selectivity for target species during separation.

The term “polymer” as used herein refers to a network of polymeric units, each polymeric unit having a polymeric backbone, side chains and crosslinking side chain(s), where the polymeric backbones of the polymeric units are cross-linked together via covalent bonds formed between the polymeric backbones and the crosslinking side chains.

The term “side chain” as used herein is not one that is used to crosslink one polymerized backbone of one polymeric unit with an adjacent polymerized backbone of another polymeric unit.

The term “crosslinking side chain” as used herein is one that is used to crosslink one polymerized backbone of one polymeric unit with an adjacent polymerized backbone of another polymeric unit.

The term “brush-like” as used herein refers to a polymeric unit having a plurality of hydrophilic polymeric side chains and/or a plurality of amphipathic polymeric side chains that extend from the polymerized backbone of the polymeric unit to form a “brush-like” structure. The “side chain” here is not one that is used to crosslink one polymerized backbone of one polymeric unit with an adjacent polymerized backbone of another polymeric unit. The side chains can be regarded as “brushes” that “dangle” off their respective polymerized backbone, and which are free to interact with external hydrophobic or hydrophilic groups.

Unless specified otherwise, the terms “comprising” and “comprise”, and grammatical variants thereof, are intended to represent “open” or “inclusive” language such that they include recited elements but also permit inclusion of additional, unrccitcd elements.

As used herein, the term “about”, in the context of concentrations of components of the formulations, typically means +/- 5% of the stated value, more typically +/- 4% of the stated value, more typically +/- 3% of the stated value, more typically, +/- 2% of the stated value, even more typically +/- 1% of the stated value, and even more typically +/- 0.5% of the stated value.

Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

Certain embodiments may also be described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of the embodiments with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

DETAILED DESCRIPTION OF OPTIONAL EMBODIMENTS

Exemplary, non-limiting embodiments of a brush-like polymer comprising a network of polymeric units, where each polymeric unit comprises a polymerized backbone with a plurality of hydrophilic polymeric side chains, a plurality of amphipathic polymeric side chains, and at least one amphipathic polymeric crosslinking side chain that extends from the polymerized backbone of one polymeric unit to crosslink with the polymerized backbone of an adjacent polymeric unit will now be disclosed.

The brush-like polymer as defined herein is not formed by physical blending of hydrophilic and/or hydrophobic polymers. Advantageously, the “brush-like” structure allows the brushlike polymer to have high mobility, allowing the functional groups to interact easily with other hydrophobic functional groups and the hydrophilic functional groups to interact with other hydrophilic groups (such as polar gas molecules). The polymeric side chains (such as the hydrophilic polymeric side chains and/or the amphipathic polymeric side chains) may be termed as the brushes.

The plurality of hydrophilic polymeric side chains may comprise hydrophilic functional groups selected from ethylene oxide, ethylene glycol, ethylenimine, acrylic acid, vinyl alcohol, vinyl amine or sodium 4-styrcncsulfonatc. Accordingly, the plurality of hydrophilic polymeric side chains may comprise hydrophilic polymers selected from poly(ethylene oxide), poly(ethylene glycol), poly(ethylenimine), poly(acrylic acid), poly(vinyl alcohol), poly(vinyl amine) or poly(sodium 4-styrenesulfonate). The plurality of hydrophilic polymeric side chains may comprise the hydrophilic functional group ethylene oxide. The plurality of hydrophilic polymeric side chains may comprise the hydrophilic polymer poly (ethylene oxide). The plurality of amphipathic polymeric side chains may comprise hydrophilic functional groups and hydrophobic functional groups. The hydrophilic functional groups may be selected from ethylene oxide, ethylene glycol, ethylenimine, acrylic acid, vinyl alcohol, vinyl amine or sodium 4-styrenesulfonate. Accordingly, the plurality of amphipathic polymeric side chains may comprise hydrophilic polymers selected from polyfethylene oxide), poly(ethylene glycol), poly(ethylenimine), poly(acrylic acid), poly(vinyl alcohol), poly(vinyl amine) or poly(sodium 4-styrenesulfonate). The hydrophilic functional group may be ethylene oxide. The plurality of amphipathic polymeric side chains may comprise the hydrophilic polymer poly(ethylene oxide). The hydrophilic functional groups may form repeating units in the plurality of amphipathic polymeric side chains or may be alternating with the hydrophobic functional groups. The hydrophobic functional groups may be selected from dimcthylsiloxanc, 1- trimethylsilyl-1 -propyne, propylene glycol, vinylpyrrolidone, ethylene, 2,3,5,6- tetrafhrorophthalonitrile-3,3,3 ',3 '-tetramethyl- l,l'-spirobisin dane-5,5',6,6'-tetrol or styrene. Accordingly, the amphipathic polymeric side chains may comprise hydrophobic polymers selected from poly(dimethylsiloxane), poly(l -trimethylsilyl- 1 -propyne), poly(propylene glycol), poly (vinylpyrrolidone), poly(ethylene, 2,3,5,6-tetrafluorophthalonitrile-3,3,3',3'- tetramethy 1-1,1 '-spirobisin dane-5,5',6,6'-tetrol) or poly (styrene). Tire hydrophobic functional group may be dimethylsiloxane. The plurality of amphipathic polymeric side chains may comprise the hydrophobic polymer poly(dimethylsiloxane). The hydrophobic functional groups may form repeating units in the amphipathic polymeric side chains or may be alternating with the hydrophilic functional groups. Advantageously, the hydrophobic functional groups in the amphipathic polymeric side chains can interact with the hydrophobic surface of an article that the brush-like polymer is coated on or forms a layer on, which allows a uniform and ultrathin coating of the layer on top of the hydrophobic surface of the article. Where the layer is a selective layer in, for example, a hollow fiber membrane, the selective layer can form the uniform and ultrathin coating on top of a gutter layer, resulting in high permeance of gas when the hollow fiber membrane is used in gas separation. Furthermore, the hydrophilic polymeric side chains can interact with the gas molecules to provide high gas solubility selectivity.

The at least one amphipathic polymeric crosslinking side chain may comprise hydrophilic functional groups and hydrophobic functional groups. The hydrophilic functional groups may be selected from ethylene oxide, ethylene glycol, ethylenimine, acrylic acid, vinyl alcohol, vinyl amine or sodium 4-styrenesulfonate. Accordingly, the amphipathic polymeric side chains may comprise hydrophilic polymers selected from poly(ethylene oxide), poly(ethylene glycol), poly(ethylenimine), poly(acrylic acid), poly(vinyl alcohol), poly(vinyl amine) or poly(sodium 4-styrenesulfonate). The hydrophilic functional group may be ethylene oxide. The amphipathic polymeric side chains may comprise the hydrophilic polymer poly(ethylene oxide). The hydrophilic functional groups may form repeating units in the amphipathic polymeric side chain or may be alternating with the hydrophobic functional groups. The hydrophobic functional groups may be selected from dimethylsiloxane, 1 -trimethylsilyl- 1 -propyne, 2, 3, 5, 6- tetrafluorophthalonitrile-3,3,3 ',3 '-tetramethyl- 1,1'- spirobisin dane-5,5',6,6'-tetrol, propylene glycol, vinylpyrrolidonc, ethylene or styrene. Accordingly, the amphipathic polymeric side chains may comprise hydrophobic polymers selected from poly(dimethylsiloxane), poly(l- trimcthylsilyl-l-propync), poly(propylcnc glycol), poly (vinylpyrrolidonc), poly(cthylcnc, 2,3 ,5,6-tetrafhiorophthalonitrile-3 ,3 , ',3 '-tetramethyl- 1 , 1 '-spirobisin dane-5 , 5 ',6, 6'-tetrol) or poly (styrene). The hydrophobic functional group may be dimethylsiloxane. The amphipathic polymeric side chains may comprise the hydrophobic polymer poly (dimethylsiloxane). The hydrophobic functional groups may form repeating units in the amphipathic polymeric side chain or may be alternating with the hydrophilic functional groups. The at least one amphipathic polymeric crosslinking side chain may comprise the same repeating units or polymers as the amphipathic polymeric side chain mentioned above. The at least one amphipathic polymeric crosslinking side chain may comprise different repeating units or polymers as the amphipathic polymeric side chain mentioned above.

The plurality of hydrophilic polymeric side chains and the amphipathic polymeric chains (as side chains and as the at least one crosslinking side chain) may be present in the brash-like polymer in a ratio in a range of about 10:1 to about 2:1. The hydrophilic polymeric side chains and the amphipathic polymeric chains (as side chains and as the at least one crosslinking side chain) may be present in the brush-like polymer in a ratio of about 5.3:1. When made into a layer and the amount of the amphipathic polymeric side chains or the amphipathic polymeric crosslinking side chains is higher, this results in a higher amount of the hydrophobic functional groups present in the layer, which causes the layer comprising the brush-like polymer to exhibit more hydrophobic characteristic. Conversely, when the amount of the hydrophilic polymeric side chains is higher, the layer comprising the brush-like polymer exhibits more hydrophilic characteristic. The brush-like polymer may comprise polymers such as poly(dimethylsiloxane) and polyethylene glycol). The brush-like polymer may be poly(dimethylsiloxane) - poly(ethylene glycol) (PDMS-PEG).

The polymerized backbone may be formed through a chain-growth polymerization. Exemplary polymerized backbone formed may include, but are not limited to, polyolefins such as polyethylene ((CH₂CH₂)_n), poly(thiol-PDMS) or poly acrylates [(-CH₂CHCO₂R) _n]. The polymerized backbone may be formed through acrylate polymerization.

As mentioned above, the brush-like polymer is made up of a network of polymeric units. The polymeric unit may be of the general formula (1):

Formula (I) wherein: n is an integer in the range between 1 to 100, all inclusive; x is an integer in the range between 1 to 100, all inclusive; z is an integer in the range between 0 to 100, all inclusive;

R is independently H or an alkyl group;

Ri is independently a hydrophilic polymeric side chain or an amphipathic polymeric side chain as defined herein;

R2 is an amphipathic polymeric crosslinking side chain that is capable of forming a crosslink with another polymeric unit of formula (I); and

R3 is an alkyl group. with the proviso that when n is 1, z is an integer in the range between 1 to 100, all inclusive.

The polymeric unit may be of the formula (I’):

Formula (I’) wherein: n is an integer in the range between 1 to 100, all inclusive; x is an integer in the range between 1 to 100, all inclusive; z is an integer in the range between 1 to 100, ah inclusive; R is independently H or an alkyl group;

Ri is independently a hydrophilic polymeric side chain as defined herein;

Rj is an amphipathic polymeric side chain that is capable of forming a crosslink with another polymeric unit of formula (I’);

Rs is an alkyl group; and R4 is independently an amphipathic polymeric side chain as defined herein.

In Formula (I), and (I’) above, the term “alkyl” denotes a monovalent straight chain or branched chain saturated aliphatic groups having from 1 to 10 carbon atoms, eg, 1 , 2, 3, 4, 5, 6, 7, 8, 9, or 10 carbon atoms. For example, the term alkyl includes, but is not limited to, methyl, ethyl, 1-propyl, isopropyl, 1-butyl, 2-butyl, isobutyl, tert-butyl, amyl, 1,2-dimethylpropyl, 1,1- dimethylpropyl, pentyl, isopentyl, hexyl, 4-methylpentyl, 1-methylpentyl, 2-methylpentyl, 3- methylpentyl, 2,2-dimethylbutyl, 3, 3 -dimethylbutyl, 1,2 -dimethylbutyl, 1,3 -dimethylbutyl, 1,2,2-trimethylpropyl, 1,1,2-trimethylpropyl, 2-ethylpentyl, 3-ethylpentyl, heptyl, 1- methylhexyl, 2,2-dimethylpentyl, 3,3-dimethylpentyl, 4,4-dimethylpentyl, 1,2-dimethylpentyl, 1,3-dimethylpentyl, 1 ,4-dimethylpentyl, 1,2,3-trimethylbutyl, 1 ,1,2-trimethylbutyl, 1 ,1 ,3- trimethylbutyl, 5-methylheptyl, 1 -methylheptyl, octyl, nonyl, decyl, and the like.

In Formula (I), and (!’) above, R3 may be a methyl group.

In Formula (I), and (I’) above, the integer n may be in the range of between 1 to 90, 1 to 85, 1 to 80, 1 to 75 or 1 to 70. In Formula (I), and (I’) above, the integer x may be in the range of between 1 to 90, 1 to 85, 1 to 80, 1 to 75 or 1 to 70. In Formula (I), and (I’) above, the integer z may be in the range of between 0 to 90, 0 to 85, 0 to 80, 0 to 75 or 0 to 70.

There is provided a brush-like polymer of the formula (II):

Formula (II) wherein:

i where — denote points of attachment of R² to respective polymeric backbones of adjacent polymeric units, each polymeric unit being of formula (II),

Wi, W2, Xi, X2, Yi, Y2, Zi, Z2, m and n are independently an integer in the range between 1 to 100, all inclusive.

In Formula (II) above, the integer Wi may be in the range of between 1 to 90, 1 to 85, 1 to 80, 1 to 75 or 1 to 70. In Formula (II) above, the integer W2 may be in the range of between 1 to 90, 1 to 85, 1 to 80, 1 to 75 or 1 to 70. In Formula (II) above, the integer Xi may be in the range of between 1 to 90, 1 to 85, 1 to 80, 1 to 75 or 1 to 70. In Formula (II) above, the integer X2 may be in the range of between 1 to 90, 1 to 85, 1 to 80, 1 to 75 or 1 to 70. In Formula (II) above, the integer Yi may be in the range of between 1 to 90, 1 to 85, 1 to 80, 1 to 75 or 1 to 70. In Formula (11) above, the integer Y2 may be in the range of between 1 to 90, 1 to 85, 1 to 80, 1 to 75 or 1 to 70. In Formula (II) above, the integer Zi may be in the range of between 1 to 90, 1 to 85, 1 to 80, 1 to 75 or 1 to 70. In Formula (II) above, the integer Z2 may be in the range of between 1 to 90, 1 to 85, 1 to 80, 1 to 75 or 1 to 70. In Formula (II) above, the integer m may be in the range of between 1 to 90, 1 to 85, 1 to 80, 1 to 75 or 1 to 70. In Formula (II) above, the integer n may be in the range of between 1 to 90, 1 to 85, 1 to 80, 1 to 75 or 1 to 70.

Exemplary, non-limiting embodiments of a method of preparing a brush-like polymer comprising a network of polymeric units will now be disclosed.

The method of preparing a brush-like polymer comprises: a) dissolving at least one homopolymcr comprising at least one hydrophilic polymeric side chain and at least one amphipathic co-polymer in a solvent to form a mixture; b) adding an initiator to the mixture formed in step a) to form a solution; and c) polymerizing the solution formed in step b) at an elevated temperature for a duration of time to form a brush-like polymer. The brush-like polymer formed may be as disclosed above.

The homopolymer or co-polymer as defined herein may be functionalized at the terminal ends. The functionalization may be acrylate functionalization. The functionalized groups may be acrylate, thiol-dimethylsiloxane or alkylene functional groups. The functionalized groups may be involved in forming the polymerized backbone of the polymeric unit through a chain-growth polymerization (such as acrylate polymerization). Exemplary polymerized backbone may include, but are not limited to, polyolefins such as polyethylene ((CEfcCEhln), poly(thiol- PDMS) or polyacrylates [(-CH₂CHCO₂R)n] . The at least one homopolymer comprising at least one hydrophilic polymeric side chain may be selected from poly(ethylene glycol) methyl ether acrylate (PEGMEMA), poly(ethylene glycol) diacrylate (PEGDA), poly(ethylene glycol) dimethacrylate (PEGDMA), poly(ethylene oxide), poly(ethylenimine), poly(acrylic acid), poly(vinyl alcohol), poly(vinyl amine) or poly(sodium 4- styrenesulfonate). The at least one homopolymer comprising at least one hydrophilic polymeric side chain may be poly(ethylene glycol) methyl ether methacrylate (PEGMEMA).

The at least one amphipathic co-polymer may comprise at least one hydrophobic polymer and at least one hydrophilic polymer. The at least one hydrophobic polymer may be selected from poly(dimethylsiloxane), poly(l-trimethylsilyl-l-propyne), polypropylene glycol), poly(vinylpyrrolidonc), poly(cthylcnc, 2,3,5,6-tctrafluorophthalonitrilc-3,3,3 ',3 '-tctramcthyl- 1,1 '-spirobi sin dane-5,5',6,6'-tetrol) or poly (styrene). The at least one hydrophilic polymer may be selected from poly(ethylene oxide), poly(ethylene glycol), poly(ethylenimine), poly(acrylic acid), poly(vinyl alcohol), poly(vinyl amine) or poly(sodium 4-styrenesulfonate). The at least one amphipathic co-polymer may comprise polymers such as poly(ethylene oxide) and poly(dimethylsiloxane). The at least one amphipathic co-polymer be the co-polymer poly (ethylene oxide dimethyl siloxane) (PEODMS).

The brush-like polymer formed may comprise polymers such as poly(dimcthylsiloxanc) and poly(ethylene glycol). The brush-like polymer formed may be poly(dimethylsiloxane) - polyethylene glycol) (PDMS-PEG).

The hydrophobic functional groups in the at least one amphipathic co-polymer may be repeating units or alternating with the hydrophilic functional groups in the respective copolymer. The hydrophilic functional groups in the at least one amphipathic co-polymer may be repeating units or alternating with the hydrophobic functional groups in the respective copolymer.

The at least one amphipathic co-polymer may form the amphipathic polymeric side chains and the amphipathic polymeric crosslinking side chain of the resultant brush-like polymer. The amphipathic polymeric side chains and the amphipathic polymeric crosslinking side chain may have the same functional groups/polymers or different functional groups/polymers . Where both are the same, the same amphipathic co-polymer is used to form both the amphipathic polymeric side chains and the amphipathic polymeric crosslinking side chain. Where both axe different, the amphipathic co-polymer is independently selected to form each of the amphipathic polymeric side chains and each of the amphipathic polymeric crosslinking side chain or the entirety of the amphipathic polymeric side chains is different from that of the amphipathic polymeric crosslinking side chain.

The method of preparing the brush-like polymer may further comprise a step of b! ) purging the solution formed in the adding step b) before the polymerizing step c). The purging step bl) may involve a gas. The gas may be argon. The purging step bl) may be undertaken at a duration in the range of about 30 minutes to about 45 minutes, about 35 minutes to about 45 minutes, or about 40 minutes to about 45 minutes.

The method of preparing the brush-like polymer may further comprise a step d) of drying the brush-like polymer formed in the polymerizing step c). The drying step d) may be undertaken at a temperature in a range of about 80 °C to about 95 °C, about 80 °C to about 90 °C or about 80 °C to about 85 °C. The drying step d) may be conducted under high vacuum. The drying step d) may be undertaken for a duration in a range of about 2 days to about 5 days, about 3 days to about 5 days.

The at least one homopolymer comprising at least one hydrophilic polymeric side chain and the at least one amphipathic co-polymer may be present in the dissolving step a) in a ratio in a range of about 1:100 to about 1:0.01.

The solvent in the dissolving step a) may be an organic solvent. The organic solvent may be selected from toluene, benzene, acetonitrile, chloroform, acetone, ethyl acetate or combinations thereof. The organic solvent may be toluene.

The at least one homopolymer comprising at least one hydrophilic polymeric side chain and the at least one amphipathic co-polymer may be present in the brush-like polymer in a ratio in a range of about 10:1 to about 2:1. The ratio of the hydrophilic and hydrophobic functional groups present in the amphipathic co-polymcr may be the same during the dissolving step a) and the resulting brush-like polymer. When made into a layer and the amount of the at least one amphipathic co-polymcr is higher, this results in a higher amount of the hydrophobic functional groups present in the layer, which causes the layer comprising the brush-like polymer as defined herein to exhibit more hydrophobic characteristic. Conversely, when the amount of the at least one homopolymer comprising at least one hydrophilic polymeric side chain is higher, the layer comprising a brush-like polymer as defined herein exhibits more hydrophilic characteristic.

The initiator in the adding step b) may be selected from benzoyl peroxide (BPO), potassium persulfate or 2,2’-Azobis(2-methylpropionitrile) (AIBN). The initiator in the adding step b) may be 2,2’-Azobis(2-methylpropionitrile) (AIBN).

The elevated temperature in the polymerizing step c) may be in the range of about 65 °C to about 85 °C, about 65 °C to about 80 °C, about 65 °C to about 75 °C, or about 65 °C to about 70 °C.

The duration of time in the polymerizing step c) may be in the range of about 30 minutes to about 60 minutes, about 35 minutes to about 60 minutes, about 40 minutes to about 60 minutes, or about 50 minutes to about 60 minutes.

The polymerizing step c) may result in the formation of a brush-like polymer having a network of polymeric units, where each polymeric unit comprises a polymerized backbone with a plurality of hydrophilic polymeric side chains, a plurality of amphipathic polymeric side chains and at least one amphipathic polymeric crosslinking side chain that extends from the polymerized backbone and where the amphipathic polymeric crosslinking side chain crosslinks between a polymerized backbone of one polymeric unit and that of an adjacent polymeric unit.

Exemplary, non-limiting embodiments of a brush-like polymer obtained from or obtainable from a method as defined herein will now be disclosed. The brush-like polymer may be as defined herein. The method may be as defined herein.

Exemplary, non-limiting embodiments of a method of forming a layer comprising a brush-like polymer as defined herein on an article will now be disclosed.

There is provided a method of forming a layer comprising a brush-like polymer as defined herein on an article comprising: a) dissolving the brush-like polymer in a solvent to form a brush-like polymer coating solution; b) dipping the article into the brush-like polymer coating solution formed in step a) for a duration of time to form the layer on the article; and c) removing the layered article from the brush-like polymer coating solution. The solvent used in the dissolving step a) may be selected from water, ethyl acetate, toluene, dimethylformamide, acetone, isopropyl alcohol, methanol, ethanol, isobutanol, and combinations thereof. The solvent used in the dissolving step a) may be ethanol.

The article, before being coated, may have an outer surface coated with a homopolymer comprising the same hydrophobic polymeric side chain as the amphipathic co-polymer used in the brush-like polymer. The homopolymer comprising the same hydrophobic polymeric side chain may be PDMS. The article may be a polyacrylonitrile-based (PAN) hollow fiber membrane. After coating, the layer comprising the brash-like polymer may comprise polymers such as poly(dimcthylsiloxanc) and poly (ethylene glycol). The brash-like polymer may be poly(dimethylsiloxane) - poly(ethylene glycol) (PDMS-PEG).

The duration of time in the dipping step b) may be in a range of about 5 seconds to about 20 seconds, about 5 seconds to about 15 second or about 5 seconds to about 10 seconds.

The concentration of the brush-like polymer coating solution formed in step a) may be in the range of about 0.01 wt% to about 10 wt%. Advantageously, the concentration of the brush-like polymer coating solution will inevitably affect the thickness of the layer being formed, and hence the gas separation performance. Accordingly, at diluted coating concentrations of the brush-like polymer coating solution, the thickness of the film is thinner, and vice versa for high coating concentration of the brush-like polymer coating solution.

The method of forming a layer comprising a brush-like polymer as defined herein on an article may further comprise a drying step d) which may be undertaken for a period of time in a range of about 18 hours to about 60 hours, about 18 hours to about 55 hours, or about 18 hours to about 50 hours. The drying step d) may be simply air-drying at room temperature or air-drying at an elevated temperature. The air-drying at room temperature may be undertaken at a temperature in the range of about 22 °C to about 25°C. The air-drying at elevated temperature may be undertaken at a temperature in the range of about 25 °C to about 35 °C or about 25 °C to about 30 °C.

Exemplary, non-limiting embodiments of a layer comprising a brush-like polymer as defined herein will now be disclosed.

Advantageously, the hydrophobic groups on the amphipathic polymeric side chain can interact with the hydrophobic surface that it is being coated on, which allows a uniform and ultrathin coating of the layer on top of the hydrophobic surface of the article. Where the layer is a selective layer in, for example, a hollow fiber membrane, the selective layer can form the uniform and ultrathin coating on top of a gutter layer, resulting in high permeance of gas when the hollow fiber membrane is used in gas separation. Furthermore, the hydrophilic polymeric side chains can interact with the gas molecules to provide high gas solubility selectivity.

The layer as defined herein may be in the form of a film. The thickness of the layer may be in the range of about 1 nm to about 350 nm, about 1 nm to about 250 nm, about 1 nm to about 150 nm, or about 1 nm to about 100 nm. After coating, the layer comprising the brush-like polymer may comprise polymers such as poly (dimethylsiloxane) and poly (ethylene glycol). The brush-like polymer may be PDMS-PEG.

Exemplary, non-limiting embodiments of an article coated with the layer comprising a brushlike polymer as defined herein will now be disclosed. The layer may be formed on the article using the method of forming a layer comprising a brush-like polymer as defined herein. The article, before being coated, may have an outer surface coated with a homopolymer comprising the same hydrophobic polymeric side chain as the amphipathic co-polymer used in the brushlike polymer. The homopolymer comprising the same hydrophobic polymeric side chain may be PDMS. The article may be a polyacrylonitrile- based (PAN) hollow fiber membrane. After coating, the layer comprising the brush-like polymer may comprise polymers such as poly(dimcthylsiloxanc) and poly(cthylcnc glycol). The brush-like polymer may be PDMS- PEG.

As an example, the article may be coated with the PDMS as a gutter layer in CO₂ gas separation to minimize intrusion. Advantageously, the dimethylsiloxane group in the PDMS-PEG brushlike polymer layer can interact with the PDMS gutter layer, which allows a uniform and ultrathin coating of the PDMS-PEG brush-like polymer layer on top of the PDMS gutter layer providing high CO₂ permeance. This interaction also allows the coating to be undertaken through the simple method of forming a layer comprising a brush-like polymer as defined herein. Furthermore, the ethylene oxide group in the PDMS-PEG brush-like polymer layer can interact with the CO₂ molecule to provide high CO₂ solubility selectivity.

Exemplary, non-limiting embodiments of a method of using an article coated with a layer comprising a brush-like polymer as defined herein, the method comprising passing a mixture for separation across the article. The article may be as defined herein. The layer comprising the brush-like polymer may be as defined herein. The mixture may be a mixture of gases. The separation may be for gas separation.

The method of using the article coated with the layer comprising the brush-like polymer as defined herein for gas separation may be for separating gas mixtures containing carbon dioxide with concentration of about 1 % to about 95%, about 1 % to about 80%>, about 1 % to about 70%, about 1% to about 60%, about 1% to about 50%, or about 1% to about 40%.

Exemplary, non-limiting embodiments of use of an article coated with a layer comprising a brush-like polymer as defined herein for separation will now be disclosed.

The article may be as defined herein. The layer comprising the brush-like polymer may be as defined herein. The separation may be gas separation. The separation may be CO₂ gas separation. As an example, in CO₂ gas separation, when the layer comprising the brush-like polymer is or comprises PDMS-PEG, it has hydrophilic and hydrophobic properties like surfactants. Advantageously, the PDMS-PEG brush-like polymer layer provides dual functionality as a superior selective layer as the dimethylsiloxane group can interact with the PDMS gutter layer, which allows a uniform and ultrathin coating of PDMS-PEG brush-like polymer layer on top of the PDMS gutter layer providing high CO₂ permeance. Furthermore, the ethylene oxide group can interact with the CO₂ molecule to provide high CO₂ solubility selectivity.

The use of the article coated with the selective layer comprising the brush-like polymer composition as defined herein for gas separation may be for separating gas mixtures containing carbon dioxide with concentration of about 1 % to about 95%, about 1 % to about 80%, about 1% to about 70%, about 1% to about 60%, about 1% to about 50%, or about 1% to about 40%.

In the present disclosure, a layer (ultra-thin film) comprising a brush-like polymer comprising a plurality of hydrophilic polymeric side chains, a plurality of amphipathic polymeric side chains and at least one amphipathic polymeric crosslinking side chain was formed by utilization of surfactant-like material with brush structures consisting of both hydrophobic and hydrophilic functional groups, thus providing dual functionalities. It is a bio-inspired strategy to fabricate TFC hollow fiber membranes via a tree-mimicking polymer network, with amphipathic components featuring multi-functionalities. The hydrophobic group of the amphipathic polymeric side chain (such as poly dimethylsiloxane (PDMS) brushes) act as the roots that can strongly cling on the gutter layer, the amphipathic polymeric side chains (such as PDMS-PEO crosslinkers) function as the xylems to enable fast gas transport, and the hydrophilic polymeric side chains (such as ethylene-oxide moieties (brushes and mobile molecules)) resemble tree leaves that selectively attract CO₂ molecules. The presence of hydrophobic functional groups (such as dimethylsiloxane) in the brushes (the polymeric side chains) provide strong interaction with gutter layer made of PDMS, which enables the formation of ultrathin film (PDMS -PEG film). Unlike many other reported strategies in surface modification of PDMS gutter layer, the present disclosure allows a direct coating of the selective layer through simple dip-coating method that can be easily adopted for commercial processes. Secondly, the presence of hydrophilic functional groups (such as ethylene oxide) in the brushes attract the gas molecules (such as CO₂ molecule) and improve their solubilities on the separation membrane. As an example, combining these two functionalities led to formation of an ultrathin thin film composite (TFC) hollow fiber membrane with a selective layer (such as PDMS-PEG selective layer). As a result, an ultrathin, at the scale of less than 100 nm and even about 26 nm, and defect-free selective layer was coated directly onto the gutter layer via a simple dip coating process, without the need of any pre-modification. A CO₂ permeance of - 2667 ± 193 GPU and a CO₂/N₂ selectivity of ~ 21 ± 0.9 that is beyond the permeanceselectivity upper bound for hollow fiber membranes has been achieved, potentially opening the possibility of scalable membrane production for commercially attractive post-combustion carbon capture and beyond. The layer (ultra-thin film) in the present disclosure using surfactant-like material is not limited for use in gas separation but may also be applicable for other membrane configuration and coating technique.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with reference to the detailed description when considered in conjunction with the non-limiting examples and the accompanying drawings, in which:

Fig i

Fig. 1 is an illustration of the synthesis of the brush-like polymer as defined herein with tree- mimicking/brush structure.

Fig, 2

Fig. 2 is an illustration of the tree-mimicking structure of PDMS-PEG through thermal-initiated radical polymerization. Fig. 3a

Fig. 3a is a series of photographs showing physical appearance of the PDMS-PEG polymers with various feed ratios of PEODMS and PEGMEMA (PDMS_0.3PEG0.7. PDMS0.5PEG_0.5, and PDMS0.7PEG0.3)

Fig. 3b

Fig. 3b shows a graph comparing the FT-IR spectra of the PDMS-PEG with various ratios of dimethylsiloxane and ethylene oxide functional groups, compared with the monomers PEODMS and PEGMEMA.

Fig. 3c

Fig. 3c shows a ¹H NMR spectra for the PDMS_0.5PEG_0.5.

Fig. 4a

Fig. 4a shows a ¹H -NMR spectra of PDMS0.3PEG0.7-

Fig. 4b

Fig. 4b shows a ¹H -NMR spectra of PDMS0.7PEG0.3-

Fig. 5

Fig. 5 is an illustration of synthesizing regular PDMS-PEG with non-brush structure, as a comparative example.

Fig. 6a

Fig. 6a is a scanning electron microscopy image showing the cross section of a PAN substrate coated with the thin film composite membrane at a scale of 100 pm.

Fig. 6b

Fig. 6b is the boxed-up portion of Fig. 6a, at a higher magnification with a scale of 100 nm.

Fig. 6c

Fig. 6c is a scanning electron microscopy image showing the magnification of PDMS layer coated on the PAN substrate at a scale of 100 nm. Fig. 6d

Fig. 6d is a scanning electron microscopy image showing the magnification of PDMS03PEG07 layer at a scale of 100 nm.

Fig. 6e

Fig. 6e is a scanning electron microscopy image showing the magnification of PDMS0.5PEG_0.5 layer at a scale of 100 nm.

Fig. 6f

Fig. 6f is a scanning electron microscopy image showing the magnification of PDMS0.7PEG0.3 layer at a scale of 100 nm.

Fig. 6g is a graph showing the time-of-flight secondary ion mass spectrometry depth profile analysis on the PDMS0.5PEG_0.5 film.

Fig. 7a

Fig. 7a is a scanning electron microscopy image showing the cross section of the thin film composite membrane formed with PDMS03PEG07 as a selective layer at high coating concentration of 1 %.

Fig. 7b

Fig. 7b is a scanning electron microscopy image showing the cross section of the thin film composite membrane formed with PDMS0.3PEG0.7 as a selective layer at medium coating concentration of 0.67%.

Fig. 7c

Fig. 7c is a scanning electron microscopy image showing the cross section of the thin film composite membrane formed with PDMS0.3PEG0.7 as a selective layer at low coating concentration of 0.44%.

Fig. 7d

Fig. 7d is a scanning electron microscopy image showing the cross section of the thin film composite membrane formed with PDMS05PEG05 as a selective layer at high coating concentration of 0.83%. Fig. 7e

Fig. 7e is a scanning electron microscopy image showing the cross section of the thin film composite membrane formed with PDMS0.5PEG_0.5 as a selective layer at medium coating concentration of 0.62%.

Fig. 7f

Fig. 7f is a scanning electron microscopy image showing the cross section of the thin film composite membrane formed with PDMS0.5PEG_0.5 as a selective layer at low coating concentration of 0.33%.

Fig. 7g is a scanning electron microscopy image showing the cross section of the thin film composite membrane formed with PDMS07PEG03 as a selective layer at high coating concentration of 8.3%.

Fig. 7h

Fig. 7h is a scanning electron microscopy image showing the cross section of the thin film composite membrane formed with PDMS07PEG03 as a selective layer at medium coating concentration of 3.7%.

Fig. 7i

Fig. 7i is a scanning electron microscopy image showing the cross section of the thin film composite membrane formed with PDMS0.7PEG0.3 as a selective layer at low coating concentration of 1.5%.

Fig. 8a

Fig. 8a is a scanning electron microscopy image showing the cross section of PAN substrate coated with PDMS.

Fig. 8b

Fig. 8b is a scanning electron microscopy image showing the cross section of Pebax 2533 coating on top of PDMS gutter layer.

Fig. 8c

Fig. 8c is a scanning electron microscopy image showing the cross section of Polyactive 4.0k coating on top of PDMS gutter layer. ig. 9a

Fig. 9a shows a graph comparing time sensitive water contact angle measurement on the PDMS-PEG and pure PDMS.

Fig. 9b

Fig. 9b shows a photograph comparing the physical appearance of PDMS-PEG dense films displaying transparency for PDMSosPEGo 7. A square was drawn as a guide on the location of the films.

Fig. 9c

Fig. 9c shows a photograph comparing the physical appearance of PDMS-PEG dense films displaying transparency for PDMS0.5PEG_0.5-

Fig. 9d

Fig. 9d shows a photograph comparing the physical appearance of PDMS-PEG dense films displaying some degree of opacity for PDMSo 7PEG03 film.

Fig. 10a

Fig. 10a shows a graph showing pure gas (CO₂ and N₂) permeance and selectivity at 3 Barg and room temperature on the TFC membranes with PDMS-PEG as a selective layer with various coating concentrations.

Fig. 10b

Fig. 10b shows a graph comparing the performance of CO₂/N₂ separation by hollow fiber membranes of the present disclosure with reported literatures. The patterned area indicates the commercially attractive membrane performance region as set by the DOE to capture at least 90% of the flue gas CO₂.

Fig. 10c

Fig. 10c shows a graph showing permeation testing of CO₂ and N₂ at various transmembrane pressure and room temperature.

Fig. lOd

Fig. lOd shows a graph comparing single gas and mixed gas testing with CO₂/N₂ at 50/50 and 15/85 mol ratio for the PDMS0.5PEG_0.5 membrane. 12. 11

Fig. 11 shows a bar chart showing the long-term stability testing for TFC hollow fiber membrane with PDMS0.5PEG_0.5 selective layer.

Fig. 12

Fig. 12 shows a bar chart showing a comparison of intrinsic CO₂ permeabilities and CO₂/N₂ selectivities of various commercial PEG-based polymers and the PEG-PDMS samples.

EXAMPLES

Non-limiting examples of the invention will be further described in greater detail by reference to specific examples, which should not be construed as in any way limiting the scope of the invention. and characterization of PDMS-PEG -like solution

Preparation of PDMS-PEG (brush-like polymer) coating solution

For the synthesis of PDMS-PEG with brush structure, in a typical process, acryloxy-terminated ethyleneoxide dimethylsiloxane-ethyleneoxide ABA block copolymer (PEODMS, obtained from Gelest Inc., Pennsylvania, United States) and poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) (obtained from Sigma Aldrich, Missouri, United States) were dissolved in toluene at 1 :10 ratio, in which a catalytic amount of initiator 2,2’-Azobis(2- methylpropionitrile) (AIBN, obtained from Sigma Aldrich, Missouri, United States) was added to the mixture. The solution was purged with argon, and reacted at 65 °C for up to 1 hour. The synthesized PDMS-PEG was collected and dried at 80°C and under high vacuum for 5 days prior to further use and characterization. The PDMS-PEG was dispersed in ethanol and used as a coating solution for selective layer formation.

The synthesis route of tree-mimicking structure PDMS-PEG network polymer as shown in Fig. 1 and Fig. 2, where polyethylene oxide with acrylate terminated (PEGMEMA) was reacted with copolymer consisting of dimethylsiloxane and ethylene oxide chains terminated with acrylate functional group (PEODMS). Upon thermal initiation, radical polymerization took place involving the acrylate groups of both types of macro-monomers. The PEODMS macromonomers having acrylate groups on both ends were responsible in building the backbone, resulting in a self-crosslinked PDMS-PEG network with pendant dimethylsiloxane and polyethylene-oxide (PEO) chains. Noticeably, the polymer synthesis following this route was completed within 1 hour under mild conditions; thus, it could be readily scaled up within existing industrial infrastructure. The PDMS-PEG had a brush-like polymer structure in which the backbone was formed by the chain-growth acrylate polymerization wherein each of the brush consisted of dimethylsiloxane and/or ethylene oxide group chains. The PDMS-PEG was self-crosslinked with its own monomer of PEODMS which had acrylate groups on both ends which were responsible in building the backbone of the PDMS-PEG.

The crosslinking process for the PDMS-PEG brush-like polymer here was through acrylateacrylate homopolymerization and initiated through simple thermal reaction, in which the crosslinking degree was controlled. At a certain crosslinking degree, the PDMS-PEG can still be dissolved in a solvent to be used as a coating solution to form thin selective film for the fabrication of TFC through a simple dip- or spray-coating method. As a result, an ultrathin selective layer of 26 nm thickness on unmodified PDMS gutter layer can be formed on the hollow fiber supports simply through dip coating. This is in comparison to using rapid UV curing of thiol-ene reaction for the crosslinking process where the crosslinked polymers containing thiol-functionalized monomers were oxidized and degraded within just one year stored under ambient conditions, which posed a challenge for the required long-term stability in industrial power plants. Furthermore, fabricating a uniform and defect free thin (< 100 nm) membrane through rapid UV curing crosslinking was extremely challenging, and even more so impractical to be adopted for hollow fiber configuration.

Characterization of PDMS_X-PEG_V (brush-like polymer) with different feed ratios

The PDMS_x-PEGy was synthesized with various feed ratios of the PEODMS and PEGMEMA, where x and y correspond to the weight ratio of PEODMS and PEGMEMA, respectively. Infrared spectra were collected using attenuated total reflection Fourier Transformed infrared (ATR- FTIR, Brucker) at a resolution of 0.1 cm-1 with 32 scans. Fourier-transform infrared (FTIR) spectroscopy was employed to analyze the successful acrylate-acrylate homopolymerization and incorporation of both monomers at different feed ratio as shown in Fig. 3b. The solid physical appearance of the synthesized PDMS-PEG as displayed in Fig. 3a, confirming the crosslinked polymer network of PDMS-PEG as compared to the liquid phase of its macromonomers. The C=C stretching vibration peak at 1620 cm'¹ of acrylate functional group displayed decreasing intensity for the PDMS-PEG samples as compared to the pure PEGMEMA. This verified the successful acrylate-acrylate polymerization to form PDMS- PEG. However, some residual C=C signal was found on all the samples despite purification and drying under high vacuum for 5 days. This suggested the existence of unreacted PEGMEM A trapped in the PDMS-PEG polymers. The CH2 scissoring, CH2 asymmetric bending, and C-O-C ether absorption bands from PEGMEMA at 1440 cm ¹, 1344 cm ¹, and 1086 cm ¹, respectively, appear on the bandwidth of all the PDMS-PEG samples, with higher intensity for samples with more PEGMEMA in the feed (i.e. C-O-C peak intensity for PDMS0.3-PEG0.7 > PDMS0.7-PEG0.3), which confirmed the incorporation of PEGMEMA into the copolymer. Vice versa, the intensity of the Si-CHs band peaks became more pronounced with more PEODMS in the feed.

The ratio of the PEODMS to PEGMEMA was estimated using ¹ H NMR as shown in Fig. 3c, Fig. 4a and Fig. 4b. A strong chemical shift of cthylcnc-oxidc can be observed at 3.51 ppm, followed by weaker signals at 3.44, 3.64, and 4.21 ppm. The proton from methyl group in the dimethylsiloxane chain showed chemical shift at 0.06 ppm. Interestingly, the ethylene and methyl group from the methacrylate of PEGMEMA appeared in all the PDMS-PEG samples at chemical shift of 5.69, 6.03, and 1.88 ppm, respectively. This indicated the presence of unreacted and trapped PEGMEMA in the PDMS-PEG samples, which aligned with the result from FTIR analysis. The other end of PEGMEMA provided methyl signals at 3.24 ppm, which accounted for both reacted and unreacted PEGMEMA. Thus, the ratio of reacted and unreacted PEGMEMA in each of the PDMS-PEG samples can be quantified. For the PDMS0.5PEG_0.5, the ratio of the unreacted to the reacted PEGMEMA was estimated to be 1 to 0.8, and the ratio of the PEODMS to PEGMEMA was estimated to be 1 to 5.3.

It was previously demonstrated that physical impregnation of PEG-based molecule can significantly enhance the CO₂ permeability while retaining the CO₂/N₂ selectivity. However, this direct impregnation could lead to leeching out issue, which could deteriorate its performance with time. Furthermore, the above strategy was only implemented on dense film, and was not explored for thin film membranes. On the other hand, the PDMS-PEG of this example inherently trapped unreacted PEGMEMA molecules, which could enhance the CO₂/N₂ separation performance. The I I NMR spectra for the other PDMS-PEG samples also showed similar patterns as shown in Fig. 4a and Fig. 4b, and their ratio comparison was summarized in Table 1.

Table 1. Comparison on the ratio of unreacted to reacted PEGMEMA and ratio of PEODMS brush to PEGMEMA brush in the PDMS-PEG samples.

2: of PDMS solution

The PDMS coating solution was prepared using the commercial elastomer kit of Sylgard® 184 (obtained from Dow Corning Pte Ltd., Singapore), using the method known in literature (Chen et al., Int. J. Hydrogen Energy 2014, 39, 5043). The silicone elastomer was mixed with the curing agent at 10:1 ratio at 75 °C until the mixture became viscous. The mixture was then dispersed in cyclohexane to form the coating solution for gutter layer formation.

3: and characterization of thin film hollow fiber membranes ion of thin film (TFC) hollow fiber membranes

The formation of thin film composite hollow fiber membranes was done through multiple dip coating process. The PAN hollow fiber was dip coated in the PDMS coating solution, followed by dip coating in PDMS-PEG coating solution. After each of the dip coating step, the fiber was air-dried overnight prior to further characterization.

The PDMS-PEG was formed into a thin film on the PAN hollow fiber substrate, wherein the

PDMS-PEG coating concentration solution was varied. Prior to PDMS-PEG coating, the substrate was coated with PDMS as a gutter layer to minimize intrusion.

Characterization of PDMS-PEG TFC hollow fiber membranes

The cross-section images of the films were taken by field emission scanning electron microscopy (FESEM, JSM-6700, JEOL). The Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) profiles were acquired using a ToF SIMS 5 instrument (IONTOF GmbH) with a primary ion source of 30 keV Bi+. The sputter ion source was 1 keV CS+ at 50 nA. Fig. 6a and Fig. 6b showed the cross-section and outer surface morphology of the PAN hollow fiber supports, respectively. It is worth noting that the outer diameter for the PAN hollow fibers used for this study was approximately 1,000 pm (Fig. 6a). With a typical 50% module packing efficiency, the current hollow fibers provide lower surface area-to-volume ratios of 2000 m² m^-3 as compared to the reported 10000 m² m^-3. Nonetheless, it is still more than 3 times higher than the flat sheet spiral wound module configuration (600 m² m^-3). The gas permeation rate on the PAN hollow fiber substrate displayed CO₂ permeance of about 105,000 GPU and CO₂/N₂ selectivity of 0.8 (Knudsen selectivity). The outer surface of PAN supports was precoated with a PDMS gutter layer with the apparent thickness of about 150 ± 50 nm as shown in Fig. 6c, resulting in an overall CO₂ permeance of about 4,500 GPU and CO₂/N₂ selectivity of 10. The intrinsic thickness of PDMS was significantly higher due to some penetration of the PDMS coating solution into the surface pore of the PAN substrate, which will be confirmed and discussed further below. The penetration thickness of PDMS into the PAN pore surface is estimated to be approximately 41 nm using the resistance model as proposed by Henis and Tripodi known in the art.

To obtain the optimal composite membrane structure, PDMS-PEG polymers were dissolved in ethanol at high, medium and low concentrations (as elaborated in Table 3). As presented in Fig. 6d to Fig. 6f and Fig. 7a to Fig. 7i, the lower coating concentration expectantly produces thinner films. While there was a clear distinction between the PAN support and the PDMS gutter layer (Fig. 6c), it was difficult to distinguish the interface between the PDMS and PDMS- PEG layer regardless of the film thickness. This was completely different from other ethyleneoxide containing commercial polymer (i.e. Pebax and Polyactive), where clear distinctions on the interface with the PDMS gutter layer can be observed (Fig. 8a to Fig. 8c). The dimethylsiloxane brushes of the PDMS-PEG polymers interacted strongly with PDMS and penetrated into the gutter layer like the roots of a tree, thus yielding a smooth interface between these two layers. It was also noticed that the PDMS0.7PEG0.3 samples displayed higher thickness compared to the other two, which might be due to the intensive inter-layer interactions that retained a high percentage of polymers on the surface. Furthermore, the PDMS0.7PEG0.3 samples showed some stacking layers toward the top surface of the film. This indicated the phase separation between the dimethylsiloxane and ethylene-oxide group in the PDMS0.7PEG0.3 film, which explains with the opacity of the film shown in Fig. 9d as compared to the other PDMS-PEG samples (Fig. 9b and Fig. 9c). At the medium and low coating concentrations (as elaborated in Table 3), it was difficult to distinguish the increase of visible film thickness on top of the PAN substrate before and after the coating of PDMS-PEG on the PDMS gutter layer (Fig. 6c vs. Fig. 6d to Fig. 6f), which suggested the formation of an ultrathin PDMS-PEG film that was likely less than 100 nm. Due to the variation in the thickness of the PDMS and the smooth blending interface between the two layers, the thickness of the PDMS-PEG layer cannot be accurately quantified from the SEM images. Time-of-flight secondary ion mass spectrometry was employed to further characterize the layer thickness of the PDMS0.5PEG_0.5 selective layer with medium coating concentration and PDMS gutter layer as shown in Fig. 6g. Negative secondary molecular ion species of CN , Si", and CH₃O were monitored to represent the PAN substrate, PDMS gutter layer, and PDMS-PEG selective layer, respectively. By tracking the depth profile of these ions, thickness of the selective and gutter layer can be determined. The CH3O-, signal starts to decline at ~ 65 nm, followed by the decrease of Si- ion intensity at - 170 nm. These observations indicate the thickness of the PDMS0.5PEG_0.5 selective layer and PDMS gutter layer were around 65 nm and around 105 nm, respectively. The thickness estimation for the PDMS gutter layer aligned well with the SEM image observation (about 150 ± 50 nm) in Fig. 6c.

Example 4: Preparation of hollow fiber substrates

The hollow fiber substrates were prepared through a dry-wet spinning process of polyacrylonitrile (PAN) using parameters as known in the art. The detailed parameters for the spinning condition can be seen in Table 2.

Table 2. Spinning parameters for PAN hollow fiber membranes.

Example 5: Water contact angle (WCA) tests on the synthesised PDMS-PEG polymer

The water contact angles (WCA) were measured using a goniometer (OCA 25, Data Physics Instruments, Germany) and applying the sessile drop technique. The WCA measurements were repeated for three times and taken for average.

The incorporation of both hydrophobic dimethylsiloxane chain and hydrophilic ethylene-oxide group into the same backbone copolymer allowed the PDMS-PEG to have amphipathic characteristic. Fig. 9a displayed the water contact angles (WCAs) of PDMS-PEG dense film samples compared to pure PDMS film. Interestingly, although all PDMS-PEG samples contained higher PEGMEMA ratio as compared to PEODMS, they all showed WCAs > 100°, suggesting their relative hydrophobicity. Furthermore, the PDMS-PEG samples with higher hydrophobic dimethylsiloxane ratio displayed lower WCAs. The WCAs for the PDMS0.7PEG0.3 sample reduced rapidly after about 10 seconds and dropped to less than 60°. The WCAs analysis suggested that the higher dimethylsiloxane ratio enables higher mobility within the polymer chain, allowing faster migration of the hydrophilic cthylcnc-oxidc group to the surface. Additionally, Fig. 9d showed that the PDMS0.7PEG0.3 dense film was opaque, in contrary to the transparent nature of the other two (Fig. 9b and Fig. 9c). It suggested that at a certain ratio of PDMS to PEG concentration in the network, it would lead to the occurrence of phase separation within the film.

Example 6: Gas permeation test

The pure gas permeation tests were conducted on a dead-end cell, in which the feed pressure was varied and the permeate was kept at atmospheric pressure. The gas permeate flow rate was measured by a universal gas flowmeter (Agilent, ADM1000), which had a detection limit of 0.5 to 1000 mL/min. The pure gas permeance, J, in GPU (1 GPU = 7.501 x 10-12 m3 (STP) m-2 s-1 Pa), can be determined according to the following equation:

, ₌ P ₌ Q ₌ Q (1)

⁷

L A P nDL_mAP Where Q was the gas permeate flow rate, D was the outer diameter of hollow fiber membranes, L_m was the effective length of the hollow fiber, and AP was the pressure difference across the membrane. The pure gas permselectivity was defined as:

Where (P/L)_x and (P/L)_y were the permeances of gases x and y, respectively. Mixed gas permeation tests for CO₂/N₂ of 50/50 and 15/85 mol%, respectively, were performed using a constant-pressure system at room temperature. The mixed gas of the 50/50 and 15/85 were premixed and certified by Air Liquide. The composition of the permeate were determined using gas chromatography by Shimadzu (GC-2014C).

The TFC membranes with ultra-thin PDMS-PEG selective layers were tested for pure gas permeation of CO₂ and N₂ at the transmembrane pressure of 3 Barg and room temperature. As summarized in Fig. 10a at the high coating concentration, the CO₂/ N₂ selectivities are comparable with their respective intrinsic selectivities of dense films, indicating the successful formation of defect free thin film of PDMS-PEG. The PDMS0.5PEG_0.5, for example, achieved a CO₂ permeance of 1,461 ± 156 GPU and CO₂/N₂ selectivity of 38.0 ± 4.5. As the coating concentration was diluted, the CO₂ permeance performance increased at the expense of CO₂/N₂ selectivity. At a medium coating concentration, the PDMS0.5PEG_0.5 could reach a CO₂ permeance of up to 2,667 ± 193 GPU with CO₂/N₂ selectivity of 21.0 ± 0.9. This was, to the best of the inventors’ knowledge, the first TFC hollow fiber that can achieve the commercial target as shown in Fig. 10b. Interestingly, although the PDMS0.7PEG0.3 had higher intrinsic CO₂ permeability as compared to the other PDMS-PEG samples, the TFC configuration displayed a lower CO₂ permeance performance, which was consistent with SEM observations in Fig. 7a to Fig. 7i. Furthermore, the phase separation in the PDMS07PEG03 film as discussed in earlier paragraphs (Fig. 9d) caused inhomogeneity that may deter its performance.

The resistance model proposed by Hcnis and Tripodi was applied to estimate the thickness of each PDMS-PEG layer. The intrinsic CO₂ permeability of PDMS is 3800 Barrer. Based on the resistance model, the thickness of the PDMS layer was estimated to be around 844 nm (the detailed calculation provided below), which was much higher than the apparent thickness determined from SEM images (Fig. 8a). It suggested that around 696 nm of PDMS thickness had intruded into the support similar to that in the literature. The thickness of each PDMS-PEG layer was then further calculated using the resistance model, and summarized in Table 3. It was worth noting that these thicknesses were estimated based on constant CO₂ permeability regardless of the thickness of the PDMS-PEG. For polymers PDMS03PEG07 and PDMS0.5PEG_0.5, the film thicknesses were below 100 nm. For example, the PDMS0.5PEG_0.5 one at medium concentration has a thickness of only 26 nm.

Table 3. Pure gas permeation testing (CO₂ and N₂) at 3 Barg and room temperature, and estimated thickness of the TFC hollow fiber with various PDMS-PEG selective layers coated with different coating concentration.

The defect-free, selective layer was formed from the tree-mimic structure of PDMS-PEG where the PDMS brushes resembled root structure creating strong interaction that enables the formation of ultrathin film as illustrated in Fig. 2. In the meantime, the PDMS crosslinkers facilitated fast CO₂ transport, and the PEG moictics played the role of tree leaves to selectively dissolve CO₂ from the feed gas stream. As a result, high CO₂ permeance and selectivity were achieved.

The membrane containing PDMS0.5PEG_0.5 exhibited optimal CO₂ permeance with CO₂/N₂ selectivity above 20, and thus it was further evaluated with various transmembrane testing pressure, long term stability, and binary mixed gas environment of CO₂/N₂ with mol ratio of 50/50 and 15/85, respectively, for typical flue gas streams. As shown in Fig. 10c, both CO₂ permeance and CO₂/N₂ selectivity stayed stable at high pressure of up to 7.5 Barg. As a comparison, other popular ethylene-oxide based TFC membranes, such as Pebax®, sufferred from CO₂ plasticization under high CO₂ partial pressure that led to adverse effect on the performance. On the other hand, the rubbery dimethylsiloxane group on the PDMS-PEG eased the plasticization effect and retained the high separation performance even at high pressure. The membrane was also shown to be stable after 144 hours of permeation testing as shown in Fig. 11. While the CO₂/N₂ selectivity was improved by ~ 26%, the CO₂ permeance only reduced by ~ 4%. This indicated that the unreacted PEGMEMA was effectively trapped inside the network of the PDMS-PEG and retained its excellent performance. Finally, mixed gas testing with CO₂/N₂ mol ratio of 50/50 and 15/85 was also conducted at 3 barg and room temperature as shown in Fig. lOd. The result from the binary gas testing was comparable to the single gas testing with slightly lower CO₂ permeance due to competitive sorption effect.

Resistance model calculations: the resistance model was proposed by Henis and Tripodi, and used in various studies. As a simplification, it was assumed that there was no penetration from any of the layer to the preceding layer. As such, the total resistance (Ri) of the composite membrane can be expressed as:

Where P is the gas permeance (in GPU) through the composite membranes, L is the total thickness of the composite membranes (in pm), P is the gas permeability (in Barrer) of the composite membranes. For the example in our study, the CO₂ permeance of the composite membrane, in which only consist of the PAN substrate and PDMS gutter layer, is 4500 GPU. In this case, the resistance from the PAN substrate can be considered negligible. Therefore, the composite membrane can be assumed to consist of PDMS layer alone. Considering the known intrinsic CO₂ permeability of PDMS of 3800 Barrer, the thickness of the PDMS in the composite membrane can be estimated as follow

Where R_sub+gutter corresponds to resistance through both substrate and gutter layer, which can be assumed to equal to R _utter (resistance through gutter layer alone). When the PDMS gutter layer is coated with thin layer of PDMS_0.5PEG_0.5, the CO₂ permeance can achieve to 2667 GPU. Considering the CO₂ intrinsic permeability of the PDMS_0.5PEG_0.5 to be 176 Barrer, the thickness of the PDMS_0.5PEG_0.5 thin film can be estimated as follow:

Where R_sub+gutter+sei corresponds to the resistance through the composite membrane consisting of substrate, gutter, and selective layer, which in this case the selective layer is the PDMS0.5PEG_0.5. Psei is the CO₂ permeability of the PDMS0.5PEG_0.5 as determined through dense film permeation testing. R_sci and L_sci corresponds to the calculated resistance and thickness of the selective layer PDMS0.5PEG_0.5, respectively. Based on this, the thickness of the PDMS0.5PEG_0.5 was determined to be around 26 nm.

7: Characterization of intrinsic

The intrinsic gas separation capacities of PDMS-PEG polymers were measured at the transmembrane pressure of 1 Barg and 35 °C. As summarized in Fig. 12, the CO₂ permeabilities of the PDMS0.7PEG0.3, PDMS0.5PEG_0.5, and PDMS0.3PEG0.7 are 301, 176, and 165 Barrer, with CO₂/N₂ sclcctivitics of 24, 27, and 33, respectively. Higher CO₂ permeability was observed for the PDMS-PEG with higher PDMS concentration, which may arise from the highly permeable structure intrinsic to PDMS material and reduction of crystallinity from the hydrogen bonding interaction of ethylene-oxide group. On the other hand, increasing ethylene-oxide content led to preferential dissolution of CO₂ inside the polymer, and thence an increase in the CO₂/N₂ selectivity. A comparison with commonly used commercial PEG-based polymers for carbon capture membranes is presented in Fig. 12, where PDMS-PEG polymers showed comparable or better performances than commercial polymers. PDMS moiety acts as a strong root to strongly attach with the surface of PDMS gutter layer; and PEG plays the role of tree leaves to selectively attract CO₂ as illustrated in Fig. 2.

Comparative Example 1: Comparison of the CO₂/N₂ permeation performance of PDMS- PEG (brush-like polymer) with PDMS-PEG non-brush structure

For the synthesis of regular PDMS-PEG with non-brush structure, in a typical process, aminopropylmethylsiloxane-dimethylsiloxane copolymer (AmPDMS, Gelest Inc., Pennsylvania, United States), poly(ethylene glycol) diglycidyl ether (PEGDGE, Sigma Aldrich, Missouri, United States), and ethanol were all mixed with a ratio of 1 :4:5. The amine epoxy reaction was conducted at 70 °C for 30 minutes, in which the reaction was quenched with cold ethanol. The concentration of the solution was diluted for the coating solution to form the thin film for TFC membrane.

As a comparison, another type of crosslinked amphiphatic polymer consisting of both dimethylsiloxane and ethylene oxide groups with regular non-brush structure was synthesized as shown in Fig. 5, wherein J, K, L, Ji, J2, Ki, K2, Li are integers of at least 1. This non-brush PDMS-PEG was also fabricated into a thin film using the same PAN hollow fibre substrate coated with PDMS gutter layer. Based on the experiments conducted, the non-brush polymer cannot be formed as thinly as the brush-polymer structure, hence leading to the lower gas separation performance. Table 4 compared the CO₂/N₂ permeation performance of the brush PDMS-PEG with the non-brush PDMS-PEG. The PDMS-PEG with non-brush structure showed a low CO₂ permeance and CO₂/N₂ selectivity. This indicated that without the brush structure, regular crosslinked amphiphatic polymer such as non-brush PDMS-PEG was not able to be fabricated into thin film for the TFC membrane. Furthermore, although the non- brush PDMS-PEG contains the ethylene oxide functional group, it did not possess excellent CO₂ selectivity. This suggests the importance of the brush structure containing the ethylene oxide group with high mobility to interact with polar molecules, such as CO₂.

Table 4. Pure gas permeation testing (CO₂ and N₂) at 3 Barg and room temperature of the TFC hollow fiber with selective layers fabricated with brush and non-brush PDMS-PEG.

Summary of Examples

Tn summary, a bio-inspired strategy to form ultrathin hollow fiber membranes was developed. The tree-mimicking structure of PDMS-PEG consisted of hydrophobic dimethylsiloxane and hydrophilic ethylene-oxide brushes with multi-functionalities, enabling direct coating of ultrathin film on the surface of PDMS gutter layer via dip coating and fast CO₂ permeation of up to 2667 ± 193 GPU and CO₂/N₂ selectivity of 21 ± 0.9. The membranes could also withstand plasticization effect and maintain stable performances over the long term. The separation capacity is commercially attractive for post-combustion carbon capture and the fabrication method is easily translatable to industrial processes. The tree-mimicking concept may open up the possibilities not only for carbon capture, but also for other membrane applications. INDUSTRIAL APPLICABILITY

The disclosed brush-like polymer, a layer comprising a brush-like polymer as defined herein, or an article coated with the layer comprising a brush-like polymer as defined herein may be used for separation, membrane configuration and coating techniques in commercially attractive post-combustion carbon capture and beyond. This is applicable to industries such as energy and electrical related technologies.

It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the ail after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.

Claims

Claims

1. A brush-like polymer comprising a network of polymeric units, each polymeric unit comprising: a) a polymerized backbone; b) a plurality of hydrophilic polymeric side chains and a plurality of amphipathic polymeric side chains extending from the polymerized backbone; and c) at least one amphipathic polymeric crosslinking side chain that extends from the polymerized backbone of one polymeric unit to crosslink with the polymerized backbone of an adjacent polymeric unit.

2. The brush-like polymer according to claim 1, wherein each polymeric unit is of the general formula (I):

Formula (I) wherein: n is an integer in the range between 1 to 100, all inclusive; x is an integer in the range between 1 to 100, all inclusive; z is an integer in the range between 0 to 100, all inclusive;

R is independently H or an alkyl group;

Ri is independently a hydrophilic polymeric side chain or an amphipathic polymeric side chain; R2 is an amphipathic polymeric crosslinking side chain that is capable of forming a crosslink with another polymeric unit of formula (I); and

R? is an alkyl group, with the proviso that when n is 1, z is an integer in the range between 1 to 100, all inclusive.

3. The brush-like polymer according to claim 1, wherein each polymeric unit is of the formula (I’):

Formula (I’) wherein: n is an integer in the range between 1 to 100, all inclusive; x is an integer in the range between 1 to 100, all inclusive; z is an integer in the range between 1 to 100, all inclusive;

R is independently H or an alkyl group;

Ri is independently a hydrophilic polymeric side chain;

Rs is an amphipathic polymeric crosslinking side chain that is capable of forming a crosslink with another polymeric unit of formula (I’);

R’, is an alkyl group; and

R4 is independently an amphipathic polymeric side chain.

4. The brush-like polymer according to any one of claims 1 to 3, wherein the hydrophilic polymeric side chains comprise hydrophilic functional groups selected from ethylene oxide, ethylene glycol, cthylcniminc, acrylic acid, vinyl alcohol, vinyl amine or sodium 4-styrenesulfonate.

5. The brush-likc polymer according to any one of claims 1 to 4, wherein the amphipathic polymeric side chains or the at least one amphipathic polymeric crosslinking side chain comprise hydrophilic functional groups selected from ethylene oxide, ethylene glycol, ethylenimine, acrylic acid, vinyl alcohol, vinyl amine or sodium 4-styrenesulfonate.

6. The brush-likc polymer according to any one of claims 1 to 5, wherein the amphipathic polymeric side chains or the at least one amphipathic polymeric crosslinking side chain further comprise hydrophobic functional groups selected from dimethylsiloxane, 1 -trimethylsilyl- 1 -propyne, propylene glycol, vinylpyrrolidone, ethylene, 2,3,5,6-tetrafluorophthalonitrile-3,3,3 ',3 '-tetramethyl- 1,1'- spirobisin dane-5,5',6,6'-tetrol or styrene.

7. The brush-like polymer according to any one of claims 1 to 6, wherein the ratio of the plurality of hydrophilic polymeric side chains and the amphipathic polymeric chains is in the range of about 10:1 to about 2:1.

8. The brush-likc polymer according to claim 1, wherein the brush-likc polymer is of the formula (II):

R2

where — denote points of attachment of R² to respective polymeric backbones of adjacent polymeric units, each polymeric unit being of formula (II),

Wi , Wr, Xi , Xr, Yj , Y2, Z1 , Z2, m and n are independently an integer in the range between 1 to 100, all inclusive.

9. A method of preparing a brush-like polymer comprising a network of polymeric units, the method comprising: a) dissolving at least one homopolymer comprising at least one hydrophilic polymeric side chain, at least one amphipathic co-polymcr in a solvent to form a mixture; b) adding an initiator to the mixture formed in step a) to form a solution; and c) polymerizing the solution formed in step b) at an elevated temperature for a duration of time to form the brush-like polymer.

10. The method according to claim 9, wherein the solvent in the dissolving step a) is an organic solvent selected from toluene, benzene, acetonitrile, chloroform, acetone, ethyl acetate or combinations thereof.

11. The method according to claim 9 or 10, wherein the initiator in the adding step b) is selected from benzoyl peroxide (BPO), potassium persulfate or 2,2’-Azobis(2- methylpropionitrile) (A1BN).

12. The method according to any one of claims 9 to 11, wherein the elevated temperature in the polymerizing step c) is in the range of about 65 °C to about 85 °C and the duration of time in the polymerizing step c) is in the range of about 30 minutes to about 60 minutes.

1 . The method according to any one of claims 9 to 12, wherein the at least one homopolymer comprising at least one hydrophilic polymeric side chain is selected from poly(ethylene glycol) methyl ether acrylate, poly(ethylene glycol) diacrylate or poly(ethylene glycol) dimethacrylate.

14. The method according to any one of claims 9 to 13, wherein the at least one co- polymer comprising at least one amphipathic polymeric side chain is poly (ethylene oxide dimcthylsiloxanc) PEODMS.

15. A method of forming a layer comprising a brush-like polymer on an article comprising: a) dissolving the brush-like polymer in a solvent to form a brush-like polymer coating solution; b) dipping the article into the brush-like polymer coating solution formed in step a) for a duration of time to form a layer on the article; and c) removing the layered article from the brush-like polymer coating solution.

16. The method according to claim 15, wherein the solvent used in the dissolving step a) is selected from water, ethyl acetate, toluene, dimethylformamide, acetone, isopropyl alcohol, methanol, ethanol, isobutanol, and combinations thereof.

17. The method according to claim 15 or 16, wherein the duration of time in the dipping step b) is in the range of about 5 seconds to about 20 seconds.

18. A brush-like polymer obtained from or obtainable from a method according to any one of claims 15 to 17.

19. A layer comprising a brush-like polymer according to any one of claims 1 to 8 or 18.

20. The layer according to claim 19, wherein the thickness of the layer is in the range of about 1 nm to about 350 nm.

21. An article coated with a layer comprising a brush-like polymer of any one of claims 1 to 8 or 18.

22. A method of using an article coated with a layer comprising a brush-like polymer of any one of claims 1 to 8 or 18, the method comprising passing a mixture for separation across the article.

23. Use of an article coated with a layer comprising a brush-like polymer of any one of claims 1 to 8 or 18 for separation.

24. The method according to claim 22 or the use according to claim 23, wherein the separation is gas separation.

25. The method according to claim 22 or the use according to claim 23, wherein the separation is for separating gas mixtures containing carbon dioxide with concentration of about 1% to about 95%.