GAS-SEPARATION MEMBRANES

This invention relates to gas-separation membranes (GSMs) and to their preparation and use.

For purifying gaseous mixtures e.g. natural gas and flue gas, the removal of undesired components can in some cases be achieved based on the relative size of the components (size-sieving).

US 8,177,891 describes GSMs comprising a continuous substantially non- porous layer comprising the polymerization product of a compound, which compound comprises at least 70 oxyethylene groups forming an uninterrupted chain of the formula -(CH2CH2O) _n - wherein n is at least 70.

US 8,303,691 describes composite membranes comprising a polymer sheet and a porous support layer for the polymer sheet, characterized in that the polymer sheet comprises at least 60wt% of oxyethylene groups and the porous support layer has flux properties defined therein.

There is a need for strong, flexible GSMs having a high permeability and being capable of discriminating well between gases (e.g. between polar and non-polar gases). Ideally such membranes can be produced efficiently at high speed and be robust and defect-free. In this manner the GSMs could be made in a particularly cost effective manner.

According to a first aspect of the present invention there is provided a gasseparation membrane comprising: a) a porous substrate; and b) a discriminating layer in contact with the porous substrate; wherein:

(i) the discriminating layer has an ethylene oxide (EO) content of more than 50 wt% and comprises a crosslinked copolymer; and

(ii) the copolymer has a number average molecular weight of at least 350kDa and comprises a (meth)acrylic copolymer backbone and pendent (meth)acrylamide groups.

In this specification the term “comprising” is to be interpreted as specifying the presence of the stated parts, steps or components, but does not exclude the presence of one or more additional parts, steps or components.

Reference to an element by the indefinite article "a" or "an" does not exclude the possibility that more than one of the element(s) is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article "a" or "an" thus usually means "at least one".

The term "NAMW ¹ as used in this specification means number average molecular weight. The NAMW values described in this specification are preferably as measured by size exclusion chromatography. In this specification the copolymer which has a number average molecular weight of at least 350kDa and comprises a (meth)acrylic copolymer backbone and pendent (meth)acrylamide groups is often abbreviated to “the curable copolymer”. When the curable copolymer has been crosslinked it is often abbreviated herein to “the crosslinked copolymer”.

Preferably the discriminating layer has an EO content of 50 wt% to 98 wt%, more preferably 55 wt% to 95 wt%.

Preferably the crosslinked copolymer provides all or substantially all of the EO content of the discriminating layer.

The crosslinked copolymer may have been crosslinked by any means, for example one may crosslink the copolymer using a crosslinking agent or by heating and/or irradiation with light. As a consequence of crosslinking, the curable copolymer typically forms the discriminating layer as a three dimensional polymeric network which is capable of discriminating between gases, e.g. between polar and non-polar gases.

Preferably the discriminating layer of the GSM is substantially non-porous. In other words, the discriminating layer preferably comprises pores having an average size (i.e. average pore size) which does not exceed the kinetic diameter of the gas molecules which are desired to be retained by (i.e. not pass through) the discriminating layer.

A suitable method to determine the average pore size of a discriminating layer is to inspect the surface thereof (typically the discriminating layer) by scanning electron microscope (SEM) e.g. using a Jeol JSM-6335F Field Emission SEM, applying an accelerating voltage of 2kV, working distance 4mm, aperture 4, sample coated with Pt with a thickness of 1 ,5nm, magnification 100 000, 3° tilted view. Preferably the discriminating layer has an average pore size (i.e. diameter) of below 10nm, more preferably below 5nm, especially below 2nm.

Another method to measure the porosity of a discriminating layer is to measure the permeance of a GSM comprising the discriminating layer to a liquid, e.g. water. Preferably the permeance of the GSM of the present invention to liquids is very low, i.e. the average pore size of the GSM is such that its pure water permeance at 20°C is less than 6.10-8m3/m2*s*kPa, more preferably less than 3.10-8m2*s*kPa.

Preferably the discriminating layer after washing and/or drying has an average thickness in the range 50 to 2,000nm, more preferably 100 to 1 ,000nm and especially 150 to 800nm, when measured from the surface of the underlying porous substrate outwards using SEM. A preferred technique to analyze the components (including the EO-content, backbone and side chain compositions) of the discriminating layer of the GSM can be done by combination of surface chemical analysis e.g. FTIR, TOF-SIMS, etc., with decomposition chemical analysis through hydrolysation of the discriminating layer with high or low pH solution (caustic soda, nitric acid, etc) and analyze the hydrolysis product by size-exclusion chromatography, NMR, HPLC-MS, GPC-MS, mass spectrometry. According to a second aspect of the present invention there is provided a method of preparing a GSM according to the first aspect of the present invention which comprises contacting a curable copolymer with a porous substrate and then curing the curable copolymer, wherein the curable copolymer has a number average molecular weight of at least 350kDa and comprises a (meth)acrylic copolymer backbone and pendent (meth)acrylamide groups.

During curing the (meth)acrylamide groups pendent on the (meth)acrylic copolymer backbone typically crosslink with each other and with any other ethylenically unsaturated groups, if present, to form the discriminating layer.

Preferably the curable copolymer comprises 5 to 200 (meth)acrylamide groups, more preferably 10 to 200 (meth)acrylamide groups.

Preferably the pendent (meth)acrylamide groups each comprise a group of the formula -N(R7)C(=O)CRs =CRgRio wherein R?, Rs , Rg and Rw are each independently H or an optionally substituted alkyl group (especially H or Ci -4-alkyl). The ethylenically unsaturated group of the (meth)acrylamide group (e.g. of formula CRs =CRgRw wherein Rs , Rg and R are as hereinbefore defined) is polymerisable and, during curing of the curable copolymer, may cross-link with other ethylenically unsaturated groups in the same or other molecules of the curable copolymer to form a three- dimensional polymeric network which provides the discriminating layer of the GSM.

In a preferred embodiment the pendent (meth)acrylamide groups each further comprise a divalent organic linking group which is covalently bonded to the (meth)acrylic copolymer backbone of the curable copolymer. The divalent organic linking group may be formed by reaction of a nucleophilic group (e.g. thiol, alcohol, amino or amine group) present on a (meth)acrylamide compound with an epoxy group pendent on the (meth)acrylic copolymer backbone (as described in more detail below).

Optionally the curable copolymer used in the method according to the second aspect of the present comprises (some degree of) crosslinking even before it is contacted with the porous substrate. For example, one or more of the components used to make the curable copolymer, or used to make the components which are reacted to form the curable copolymer, is a crosslinking agent.

Typically the curable copolymer is contacted with the porous substrate by a process comprising applying to the porous substrate a composition comprising the curable copolymer and an inert solvent. Optionally the composition comprises one or more further ingredients, e.g. one or more initiators (e.g. thermal and/or photoinitiators) and/or one or more surfactants.

The amount of inert solvent present in the composition used to form the discriminating layer is preferably in the range of 40 to 99 wt%, more preferably 50 to 90 wt%, relative to the weight of the composition. Preferably the composition used to form the discriminating layer comprises a surfactant, e.g. 0.1 to 5 wt% and especially 0.2 to 2 wt% of surfactant, relative to the total weight of the composition.

Preferred surfactants are ionic and non-ionic surfactants, for example ethoxylated and alkoxylated fatty acids, ethoxylated amines, ethoxylated alcohol, alkyl and nonyl-phenol ethoxylates, ethoxylated sorbitan esters, and EO/PO copolymers, in which EO is ethylene oxide and PO is propylene oxide . The most preferred surfactant is a polyether-modified acryl functional polydimethylsiloxane (available as UV-3530 from Byk).

Optionally the composition used to form the discriminating layer comprises one or more further adjuvants, binders, etc. (e.g. in an amount of up to 1 .0wt% %, relative to the total weight of the composition).

Inert solvents are not curable and do not cross-link with any component of the composition. Examples of inert solvents include water, alcohol-based solvents, ether- based solvents, amide-based solvents, ketone-based solvents, sulfoxide-based solvents, sulfone-based solvents, nitrile-based solvents and organic phosphorus- based solvents. Examples of alcohol-based solvents include methanol, ethanol, isopropanol, n-butanol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol and mixtures comprising two or more of the foregoing.

Examples of inert solvents include dimethyl sulfoxide, dimethyl imidazolidinone, sulfolane, N-methyl pyrrolidone, dimethyl formamide, acetonitrile, acetone, 1 ,4- dioxane, 1 ,3-dioxolane, tetramethyl urea, hexamethyl phosphoramide, hexamethyl phosphorotriamide, pyridine, propionitrile, butanone, cyclohexanone, tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran, ethylene glycol diacetate, cyclopentylmethylether, methylethylketone, ethyl acetate, y-butyrolactone and mixtures comprising two or more thereof. Especially preferred inert solvents include methyl ether ketone, n-butyl acetate, ethyl acetate, cyclopentyl methyl ether and 2- methyltetrahydrofuran.

The inert solvent optionally comprises a single inert solvent or a combination of two or more inert solvents. Preferred inert solvents include C1-4 alcohols (e.g. methanol, ethanol and propan-2-ol), diols (e.g. ethylene glycol and propylene glycol), triols (e.g. glycerol), carbonates (e.g. ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, di-t-butyl dicarbonate and glycerin carbonate), dimethyl formamide, acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, 2-methyl tetrahydrofuran, cyclopentyl methyl ether, N-methyl-2-pyrrolidinone and mixtures comprising two or more thereof. A particularly preferred inert solvent is n-butyl acetate, methyl ethyl ketone or ethyl acetate. In one embodiment the inert solvent has a low boiling point e.g. a boiling point below 100°C. Solvents having a low boiling point can be easily removed after curing by evaporation, avoiding the need for a washing step for removal of the solvent. The curable copolymer I composition which may be used to form the discriminating layer may be cured by any suitable technique, for example by thermal curing, and/or radiation curing, and/or electron beam curing. Suitable radiation curing techniques include curing, gamma rays, x-rays and especially ultraviolet light or an accelerated electron beams. Suitable thermal curing techniques include radiation heating (e.g. infrared, laser and microwave), convection and conduction heating (hot gas, flame, oven and hot shoe), induction heating, ultrasonic heating and resistance heating.

After the curable copolymer has been cured to form the discriminating layer all or substantially all of the ethylenically unsaturated groups which were present in the pendent (meth)acrylamide groups are no longer unsaturated because they have crosslinked with other ethylenically unsaturated groups during the curing process.

Preferred thermal curing processes to form the discriminating layer comprise heating the curable copolymer (e.g. heating a composition comprising the curable copolymer) to an elevated temperature, e.g. a temperature in the range 30 to 120°C, especially 55 to 95 °C. Typically thermal curing is performed for a period of 2 to 48 hours, especially 10 to 24 hours. Preferably the thermal curing is performed in the absence of oxygen, e.g. under a blanket of nitrogen.

Examples of suitable thermal initiators include organic peroxides, for example ethyl peroxide and benzyl peroxide; hydroperoxides, e.g. methyl hydroperoxide; acyloins, e.g. benzoin; certain azo compounds, e.g. a,a'-azobisisobutyronitrile and y, y'- azobis(y-cyanovaleric acid); persulfates; peracetates, e.g. methyl peracetate and tertbutyl peracetate; peroxalates, e.g. dimethyl peroxalate and di(tert-butyl) peroxalate; disulfides, e.g. dimethyl thiuram disulfide; and ketone peroxides, e.g. methyl ethyl ketone peroxide. When the composition comprises a thermal initiator curing is preferably performed at a temperature in the range of from about 30°C to about 150°C, especially from about 40°C to about 110°C. Preferable temperatures will be especially from 60 to 90 °C.

Photo-initiators are usually required when the curing uses light, for example ultraviolet (“UV”) light.

Preferred photo-initiators for use in free radical UV cure include, but are not limited to Radical Type I and/or type II photo-initiators.

Examples of radical type I photo-initiators are as described in WO 2007018425, page 14, line 23 to page 15, line 26, which are incorporated herein by reference thereto.

Examples of radical type II photo-initiators are described in W02007018425, page 15, line 27 to page 16, line 27, which are incorporated herein by reference thereto. In case radical type II photo-initiators are used, preferably a synergist is also added. Preferred examples of synergists include, but are not limited to triethylamine, triethanolamine, methyl diethanolamine, ethyl 4-(dimethylamino)benzoate, 2- butoxyethyl 4-(dimethylamino)benzoate, 2-prop-2-enoyloxyethyl 4- (dimethylamino)benzoate and 2-ethylhexyl 4-(dimethylamino) benzoate. A single type of initiator may be used or a combination of several different types of initiator may be used.

In view of the foregoing, the method of the second aspect of the present invention preferably comprising applying a curable composition to the porous substrate and curing the composition, wherein the curable composition comprises:

(a) 0.5 to 25 wt%, more preferably 1 to 15 wt%, of the curable copolymer;

(b) 40 to 99 wt%, more preferably 80 to 98 wt%, of inert solvent(s);

(c) 0.01 to 5 wt%, more preferably 0.05 to 2 wt%, of surfactant; and

(d) 0 to 8 wt%, more preferably 0.1 to 5 wt%, of initiator.

Preferably the amount of (a) + (b) + (c) + (d) adds up to 100%. This does not exclude the presence of other components other than (a), (b), (c) and (d) but it sets the total amount of these four components. In one embodiment the composition consists solely of components (a), (b), (c), and (d).

Inert solvent(s) present in the curable composition do not cure during the method of the second aspect of the present invention and may be removed by evaporation.

The preferred curing method to form the discriminating layer comprises irradiation of the curable copolymer (or more typically a composition comprising the curable copolymer) using ultraviolet light.

Suitable conditions for preparing the discriminating layer are illustrated in the Examples section below. By adjusting the crosslinking (i.e. curing) time, temperature and the ratio of components one may tailor the degree of crosslinking as desired.

In the second aspect of the present invention a composition comprising the curable copolymer (often abbreviated herein to “the composition used to form the discriminating layer”) is preferably applied to the porous substrate by a coating process. Examples of coating processes include slot die coating, slide coating, air knife coating, roller coating, screen-printing, and dipping. Depending on the used technique and the desired end specifications, it might be necessary to remove excess composition from the porous substrate by, for example, roll-to-roll squeeze, roll-to- blade or blade-to-roll squeeze, blade-to-blade squeeze or removal using coating bars.

Advantageously the GSMs of the present invention avoid the need for a gutter layer between the discriminating layer and the porous substrate. This leads to lower raw materials costs and a simpler, cheaper manufacturing process for the GSMs.

The target value of H2S permeance for the GSMs of the present invention is below 700 GPU. Thus the present invention enables the preparation of GSMs in which the discriminating layer is not in contact with a gutter layer, e.g. not in contact with any layer comprising Si-CHs groups. Gas-separation membranes free from Si-CHs groups and in fact free from organosilicon groups may be prepared by the present invention. Thus the process according to the second aspect of the present invention enables one to use a porous substrate which is free from gutter layers. Preferably the composition used to prepare the discriminating layer is applied to the porous substrate in a roll-to-roll process having high tension forces at unrolling and/or rolling the porous substrate of at least 50N/m ² . In even more preferred process the tension forces of unrolling or rolling the porous substrate are at least 100N/m ² .

The composition used to prepare the discriminating layer is preferably radiation- curable. Preferably the time of start of irradiation to cure the composition begins within 90 seconds, more preferably within 75 seconds, most preferably within 60 seconds, of the application of that composition to the porous substrate.

Suitable sources of radiation include mercury arc lamps, carbon arc lamps, low pressure mercury lamps, medium pressure mercury lamps, high pressure mercury lamps, swirl flow plasma arc lamps, metal halide lamps, xenon lamps, tungsten lamps, halogen lamps, lasers and ultraviolet light emitting diodes. Particularly preferred are UV emitting lamps of the medium or high pressure mercury vapour type. In addition, additives such as metal halides may be present to modify the emission spectrum of the lamp. In most cases lamps with emission maxima between 200 and 450nm are particularly suitable.

The energy output of the irradiation source is preferably from 20 to 1000W/cm, preferably from 40 to 500W/cm but may be higher or lower as long as the desired exposure dose can be realized.

Irradiation in order to cure the composition used to prepare the discriminating layer may be performed once or more than once.

In order to produce sufficiently flowable composition for use in a high speed coating machine, the composition used to form the discriminating layer preferably has a viscosity below 4000m Pa s when measured at 25°C, more preferably from 0.4 to WOOmPa s when measured at 25°C. Most preferably the viscosity of the composition used to prepare the discriminating layer is from 0.4 to 500mPa.s when measured at 25°C. For coating methods such as slide bead coating the preferred viscosity is from 1 to 100mPa.s when measured at 25°C. The desired viscosity is preferably achieved by controlling the amount of inert solvent in the composition used to prepare the discriminating layer and/or by appropriate selection of the components of the composition and their amounts.

With suitable coating techniques, coating speeds of at least 5m/min, e.g. at least 10m/min or even higher, such as 15m/min, 20m/min, 25m/min or even up to 10Om/min, can be reached. In a preferred embodiment the composition used to form the discriminating layer is applied to the porous substrate at a coating speed as described above.

While it is possible to prepare the GSMs of the present invention on a batch basis with a stationary porous substrate, it is much preferred to prepare them on a continuous basis using a moving porous substrate, e.g. the porous substrate may be in the form of a roll which is unwound continuously or the porous substrate may rest on a continuously driven belt. Using such techniques the composition used to form the discriminating layer can be applied on a continuous basis or it can be applied on a large batch basis. Removal of any inert solvent present in the composition used to form the discriminating layer can be accomplished at any stage after the composition has been applied to the porous substrate, e.g. by evaporation or drying. Thus in a preferred process for making the GSMs of the present invention, the composition used to form the discriminating layer is applied continuously to a porous substrate by means of a manufacturing unit comprising one or more composition application stations, one or more curing stations and a GSM collecting station, wherein the manufacturing unit comprises a means for moving the porous substrate from the first to the last station (e.g. a set of motor driven pass rollers guiding the substrate through the coating line). The manufacturing unit optionally comprises one composition application station which applies the composition used to prepare the discriminating layer, e.g. a slide bead coater. The unit optionally further comprises one or more drying stations or IR-heating stations, e.g. for drying the final GSM.

A preferred process according to the second aspect of the present invention further comprises the step of preparing the curable copolymer by a process comprising reaction of a (meth)acrylamide compound with a polymer comprising a (meth)acrylic copolymer backbone and epoxy groups pendant on the (meth)acrylic copolymer backbone.

The polymer comprising a (meth)acrylic copolymer backbone and epoxy groups pendant on the (meth)acrylic copolymer backbone is hereinafter abbreviated to “the epoxy polymer”.

Preferred (meth)acrylamide compounds comprise a nucleophilic group (e.g. thiol, alcohol, amino or amine group), especially a primary, secondary or tertiary amino group (i.e. amino group not amide group, therefore without an adjacent carbonyl group). The function of the nucleophilic group is to react with epoxy groups pendent on the (meth)acrylic copolymer backbone of the epoxy polymer, thereby forming pendent (meth)acrylamide groups.

Preferred (meth)acrylamide compounds are of the formula:

R ₅ R6N-L-N(R ₇ )C(=O)CR8 =CR ₉ RIO

. wherein:

Rs , Re R ₇ , RS , Rg and R are each independently H or an optionally substituted alkyl group (especially H or Ci-4-alkyl); and

L is a divalent organic linking group (e.g. of formula -(CH2) _n - wherein n has a value of 1 to 7.

Preferred (meth)acrylamide compounds include DMAPMAA (N-[3-(dimethylamino)propyl]methacrylamide ), DMAPAA (N-[3-(dimethylamino) propylacrylamide), 2-aminoethylmethacrylamide hydrochloride, 2- aminoproylmethacrylamide hydrochloride, 2-aminoethylmethacrylate hydrochloride, 2- aminopropylmethacrylate hydrochloride and mixtures comprising two or more of the foregoing.

In this preferred process for preparing the curable copolymer, the weight ratio of the (meth)acrylamide compound to epoxy polymer is preferably 1 :100 to 1 :5, more preferably 1 :50 to 3:20.

Reaction of a (meth)acrylamide compound with the epoxy polymer is preferably performed in the presence of catalyst which increases the rate of reaction, for example in the presence of an acid (e.g. trifluoroacetic acid, acetic acid, hydrochloric acid or sulfuric acid or a mixture comprising two or more of the foregoing). Preferably the acid catalyst, when used, is present in an amount of 90 mole% to 110 mol% relative to the number of moles of (meth)acrylamide compounds present. The preferred catalyst is trifluoroacetic acid because this is particularly effective at catalyzing reaction of the amino group in a (meth)acrylamide compounds with the epoxy groups of the epoxy polymer. The resultant N-bindings/links can be characterized as ammonium via FT-IR analysis, ion-exchange capacity and zeta potential measurements.

Thus the (meth)acrylic copolymer backbone of the curable copolymer may be linked to the pendent (meth)acrylamide groups through pendent residues of the epoxy groups that were present in the epoxy polymer .

Another preferred process according to the second aspect of the present invention comprises preparation of the epoxy polymer by a process comprising copolymerisation of one or monomers comprising an epoxy group and one or more monomers which are free from epoxy groups, preferably in the presence of a crosslinking agent. For example, the epoxy polymer may be prepared by a process comprising polymerization of a composition comprising the following components:

(i) an ethylenically unsaturated monomer comprising only one ethylenically unsaturated group and at least one epoxy groups (often abbreviated herein to “epoxy monomer”); and

(ii) an ethylenically unsaturated monomer comprising an (meth)acrylic group and a poly(ethylene oxide) group (often abbreviated herein to “PEG monomer”); optionally (iii) one or more further monomers comprising (an) acrylic group(s) (e.g. 2 or more acrylic groups); optionally (iv) an inert solvent; and optionally (v) an initiator (especially a thermal initiator).

The above process for preparing the epoxy polymer is preferably performed using one or more of the following process conditions:

(a) an elevated temperature, e.g. a temperature in the range 30 to 120°C, especially 55 to 95 °C ;

(b) in the absence of oxygen, e.g. under a blanket of nitrogen; and

(c) for a period of 2 to 48 hours, especially 10 to 24 hours.

Preferably the epoxy monomer (i) is free from polyethylene oxide) groups. Preferably the PEG monomer (ii) is free from epoxy groups.

The epoxy polymer arising from polymerization of the above composition preferably comprises acrylic groups.

Preferably the epoxy monomer (component (i)) comprises an ethylenically unsaturated group e.g. of the formula CH2=CR ⁴ -C(O)- , especially a (meth)acrylate group (e.g. CH2=CR ⁴ -C(O)O- group, wherein each R ⁴ independently is H or CH3).

Examples of preferred epoxy monomers include glycidyl (meth)acrylate, allyl glycidyl ether, alpha-glycidyl ether, omega-acrylate polyethylene glycol) and (3,4-epoxycyclohexyl)methyl (meth)acrylate .

The amount of epoxy monomer present in the composition used for preparing the epoxy polymer is preferably in the range of 0.5 to 25wt%, more preferably 1 to 20wt%, and especially 2 to 15wt%, relative to the weight of the composition.

The PEG monomers comprising an acrylic group (component (ii)) preferably comprise a CH2=CR ⁴ -C(O)- group, especially a (meth)acrylate group (e.g. CH2=CR ⁴ -C(O)O-), wherein each R ⁴ independently is H or CH3.

Preferred PEG monomers which may be used as component (ii) of the above composition include methoxy-poly(ethylene glycol) acrylate, methoxy-poly(ethylene glycol) methacrylate, poly(ethylene glycol) acrylate, polyethylene glycol) methacrylate, bisphenol A ethoxylate acrylate, neopentyl glycol ethoxylate acrylate, propanediol ethoxylate acrylate, butanediol ethoxylate acrylate, hexanediol ethoxylate acrylate and combinations comprising two or more thereof.

The amount of PEG monomer (i.e. component (ii)) present in the composition used to make the epoxy polymer is preferably in the range of 10 to 80wt%, more preferably 30 to 75wt%, and especially 40 to 70wt%, relative to the weight of the composition.

Further other monomers (i.e. component (iii)) comprising (meth)acrylic groups (e.g. CH2=CR ⁴ -C(O)- groups), especially (meth)acrylate groups (e.g. CH2=CR ⁴ -C(O)O- groups) may be added to the composition used to make the epoxy polymer, wherein each R ⁴ independently is H or CH3.

Preferred further monomers include crosslinking agents. Examples of such crosslinking agents include poly(ethylene glycol) (di)acrylate, poly(ethylene glycol) (di)methacrylate, poly(ethylene glycol) (di)acrylamide, bisphenol A ethoxylate (di)acrylate, neopentyl glycol ethoxylate (di)acrylate, propanediol ethoxylate (di)acrylate, ethoxylated glycerol triacrylate, ethoxylated trimethylolpropane triacrylate, ethoxylated pentaerythritol tetraacrylate, ethoxylated dipentaerythritol polyacrylate and combinations of two or more thereof.

The most preferred further monomers are crosslinking agents, especially crosslinking agents comprising at least two acrylic groups. The amount of further monomers (e.g. crosslinking agent(s)) when present in the composition used to make the epoxy polymer is preferably in the range of 0.5 to 10wt%, and especially 1 to 5wt%, relative to the weight of the composition.

Preferably the composition used to make the epoxy monomer comprises an inert solvent (i.e. component (iv)). Examples of inert solvents are described above in relation to the composition used to form the discriminating layer.

Preferably the composition used to form the epoxy monomer is free from water, even when the epoxy monomer is water-soluble. However if necessary one may include water in the composition as part of the inert solvent, preferably 10 wt% or less, more preferably 5 wt% or less and most preferably 0 wt%, relative to the total weight of inert solvent present in the composition. Surprisingly omitting water from the composition used to form the epoxy monomer results in fewer defects in the resultant discriminating layer.

The amount of inert solvent present in the composition used to form the epoxy monomer is preferably in the range of 40 to 99 wt%, more preferably 50 to 90 wt%, relative to the weight of the composition.

The preferred curing will provide crosslinking of the acrylate and/or acrylic monomer and further monomers via the ethylene unsaturated bonds to form the epoxy monomer.

The composition used to form the epoxy monomer preferably comprises an initiator (i.e. component (v)), e.g. a thermal initiator and/or a photo-initiator (examples of which are provided above in relation to formation of the discriminating layer). Examples of initiators are described above in relation to the composition used to form the discriminating layer.

Preferably the composition used to form the epoxy monomer comprises 8 wt% or lower, more preferably 0.005 to 8 wt%, especially 0.01 to 5 wt% and more especially 0.1 to 3 wt% of initiator.

In a preferred embodiment the epoxy polymer comprises a group of Formula

(1 ):

Formula (1 ) wherein: m and n are each independently integers having greater than 1 ; the value of (m+n) is greater than 550; q is an integer having a value of from 3 to 23;

X is an epoxy-containing group; each R ¹ and R ² independently is H or an optionally substituted alkyl group; and R ³ is H or an optionally substituted alkyl or an optionally substituted phenyl group.

When R ¹ , R ² or R ³ is an optionally substituted alkyl group it is preferably an optionally substituted Ci-4-alkyl group.

The optional substituent’s which may be present in R ¹ , R ² or R ³ are preferably each independently selected from H or CH3.

The value of q influences the polarity of the discriminating layer, with higher values of q resulting in discriminating layers of higher polarity. Preferably q has a value of 6 to 20, for example 9 to 18. When q has a value above 23 crystallization of poly(ethylene glycol) in the composition used to form the epoxy polymer can occur which can adversely affect the performance of the resultant GSM.

In our experiments we observed that the value of (m+n) can influence how much of the composition used to form the discriminating layer is impregnated into the porous substrate and how much will stay on top of the porous substrate to form a part of the discriminating layer external to the porous substrate. On the one hand, when the value of (m+n) is below 550, the composition used to form the discriminating layer is more likely to fully impregnate into the porous substrate without leaving any observable composition on top of the porous substrate. As a result, the GSM can have performance shortcomings as described in more detail below in relation to the dying test. On the other hand, when the value of (m+n) is above 2,600, the curable composition used to form the discriminating layer is more likely to impregnate the porous substrate little or not at all. As a consequence the composition used to form the discriminating layer is entirely or almost entirely on top of the porous substrate and the bond between the discriminating layer and the porous substrate may, as a result, be weak. However when the value of (m+n) is from 550 to 2,600 on curing, the composition used to form the discriminating layer partially impregnates the porous substrate and (after post-modification steps described below) a discriminating layer is formed on top of and to some extent within the pores of the porous substrate leading to GSMs having advantageous properties.

Preferably the value of (m+n) is in the range 750 to 2,000, more preferably in the range 900 to 1 ,500.

The numbered average molecular weight (NAMW) of the copolymer refers to its NAMW prior to crosslinking, i.e. prior to conversion of the copolymer to the crosslinked copolymer. Thus the copolymer used to make the crosslinked copolymer has a NAMW of at least 350 kDA and the crosslinked copolymer will have a much higher NAMW due to the crosslinking.

Preferably the epoxy polymer and/or the curable copolymer has a numbered averaged molecular weight (NAMW) in the range 350 kDa to 10000 kDa, more preferably in the range 2000 kDa to 9000 kDa and especially in the range 2500 kDa to 7500 kDa. The NAMW may be determined by gel permeation chromatography, e.g. as described below in more detail.

Preferred Composition for making the Epoxy Polymer

In view of the foregoing, the composition used to prepare the epoxy polymer preferably comprises: a. 0.5 to 25 wt%, more preferably 2 to 15 wt%, of component (i) (especially an epoxymonomer having only one curable acrylic group); b. 10 to 80 wt%, more preferably 40 to 70 wt%, of component (ii) (especially a PEG- monomer having only one curable acrylic group); c. 0.5 to 10 wt%, more preferably 1 to 5 wt%, of component (iii) (especially a crosslinking agent); d. 40 to 99 wt%, more preferably 50 to 90 wt%, of component (iv) (inert solvent); e. 0 to 8 wt%, more preferably 0.005 to 8 wt%, of component (v) (initiator).

Preferably the amount of (i) + (ii) + (iii) + (iv) + (v) in this preferred composition adds up to 100%. This does not exclude the presence of other components other than (i), (ii), (iii), (iv) and (v) but it sets the total amount of these four components. In one embodiment the composition consists solely of components (i), (ii), (iii), (iv) and (v).

Suitable crosslinking agents, inert solvents and initiators are as described above in relation to the discriminating layer.

One may influence the ratio of m:n in Formula (1 ) by controlling the molar ratio of component (i) to (ii) in the above composition. For example, by increasing the molar ratio of component (i) to component (ii) one may increase the ratio of m to n in Formula (1 ) and therefore increase the ratio of m:n in the epoxy polymer and in the curable copolymer derived therefrom.

One may influence the absolute values of m and n in Formula (1 ) by controlling the copolymerization time and temperature for components (i) to (v), e.g. increasing the copolymerization time will increase the absolute values of m and n in Formula (1 ).

The value of q in Formula (1 ) is derived from the number of consecutive ethylene oxide groups present in component (ii). For example, if component (ii) is a PEG- monomer comprising a chain of 20 consecutive ethylene oxide groups then q in Formula (1 ) will have a value of 20.

The value of m and n in the epoxy polymer may be calculated from, for example, the NAMW of the epoxy monomer. One may also use other techniques such as size exclusion chromatography and epoxy content to determine the value of m and n in the epoxy monomer.

The values of m, n, (m+n) and q may also be calculated from the amounts and identity of the components used to form the epoxy monomer. Where the amounts and identity of the components used to form the epoxy monomer are not known, for example where the epoxy monomer (or GSM derived therefrom) has been obtained from a supplier who refuses to provide this information, one may determine the identity and amounts of components from which the GSM was obtained by analysis of the GSM, e.g. using pyrolysis and gas chromatography. A more preferred technique to analyze the components of the GSM is to hydrolyze the discriminating layer and analyze the hydrolysis products by size-exclusion chromatography or mass spectrometry. This method may be used to determine, for example, the value of (m+n) and q. This technique is particularly useful for determining the identity and ratio of monomers used to form the GSM. A suitable pyrolysis and gas chromatography technique which may be used to determine the composition of the discriminating layer in a GSM is described in the paper by H. Matsubara and H. Ohtani entitled “Rapid and Sensitive Determination of the Conversion of UV-cured Acrylic Ester Resins by Pyrolysis-Gas Chromatography in the Presence of an Organic Alkali” in Analytical Sciences, 2007, 23(5), 513.

The epoxy content of the epoxy polymer may be determined by wet chemical analysis, for example a wet chemical analysis method in which epoxy groups are reacted with HBr and the obtained result is a number of epoxy groups per unit weight of the epoxy polymer.

The value of (m+n) may also be determined from the epoxy content and NAMW of the epoxy polymer (e.g. by GPC analysis).

The primary purpose of the porous substrate is to provide the GSM with mechanical strength without materially reducing gas flux.

The porous substrate is typically open-pored (before it is converted into the GSM), relative to the discriminating layer. Typically the porous substrate is sufficiently porous to allow a composition from which the discriminating layer is derived to enter the pores and partially impregnate the porous substrate.

The porous substrate preferably comprises one, two or more sheet materials. For example, in a preferred embodiment the porous substrate comprises a non-woven backing sheet as porous support (e.g. to provide mechanical strength). In this embodiment, the discriminating layer is preferably in contact with the backing sheet and optionally adheres it to the non-woven backing sheet. Examples of suitable nonwoven backing sheets which may be used as porous support (e.g. for providing mechanical strength) include microporous organic and inorganic membranes, woven or non-woven fabric. The non-woven backing sheet may be constructed from any suitable material. Examples of such materials include polysulfones, polyethersulfones, polyimides, polyetherimides, polyamides, polyamideimides, polyacrylonitrile, polycarbonates, polyesters, polyacrylates, cellulose acetate, polyethylene, polypropylene, polyvinylidenefluoride, polytetrafluoroethylene, poly(4-methyl 1 - pentene), polyacrylonitrile and especially polyesters. One may use a commercially available porous sheet material as the backing sheet, if desired. Alternatively one may prepare the porous sheet material using techniques generally known in the art for the preparation of microporous materials.

The porous substrate may be bonded to the discriminating layer by partial permeation and curing of the composition used to form the discriminating layer. Preferably the porous substrate comprises a coating of polyacrylonitrile (PAN), polysulphone (PSf), polyether ether ketone (PEEK) and/or polytetrafluoroethylene (PTFE).

Examples of suitable porous substrates which are particularly good at receiving the composition used to form the discriminating layer include PAN, PSf, and PTFE.

Optionally the porous substrate or a component thereof, especially the backing sheet, has been subjected to a corona discharge treatment, glow discharge treatment, flame treatment, ultraviolet light irradiation treatment or the like, e.g. for the purpose of improving its wettability and/or adhesiveness.

The porous substrate preferably comprises a porous coating layer which has pores that have an average diameter at the surface which is smaller than the average diameter half way through the porous sheet material. In this embodiment, the pores half way through the porous sheet material preferably have an average diameter of 0.001 to 10pm, more preferably 0.01 to 1 pm, when measured half way through the porous sheet. Furthermore, the pores preferably have a smaller average diameter at the surface of the porous substrate, e.g. an average diameter of 0.001 to 0.1 pm, preferably 0.005 to 0.05pm. The pore diameters may be determined by, for example, viewing the surface of the porous substrate before it is converted to the GSM by scanning electron microscopy (“SEM”) and by cutting through the porous substrate and measuring the diameter of the pores half way through the porous substrate, again by SEM. The porosity at the surface of the porous substrate may also be expressed as a % porosity, i.e.

% porosity = 100% x (area of the surface which is missing due to pores) (total surface area)

The areas required for the above calculation may be determined by inspecting the surface of the porous substrate by SEM. Thus, in a preferred embodiment, the porous substrate has a % porosity >1 %, more preferably >3%, and especially >10%. In contrast, the porosity of the porous substrate comprising a gutter layer (e.g. PTMSP or PDMS) was <1 %.

The porosity of the porous substrate may also be expressed as a CO2 gas permeance (units are m ³ (STP)/m ² .s.kPa). Preferably the porous substrate has a CO2 gas permeance of 5 to 150 x 10’ ⁵ m ³ (STP)/m ² .s.kPa, more preferably of 5 to 100 x 1 O’ ⁵ m ³ (STP)/m ² .s.kPa, most preferably of 7 to 70 x 10’ ⁵ m ³ (STP)/m ² .s.kPa.

In contrast, when the porous substrate comprised a gutter layer (e.g. PTMSP or PDMS) the CO2 gas permeance of the porous substrate was much lower, typically below 5 x 10’ ⁵ m ³ (STP)/m ² .s.kPa.

Alternatively the porosity of the porous substrate may be characterised by measuring the N2 gas flow rate through the porous substrate. Gas flow rate can be determined by any suitable technique, for example using a Porolux™ 1000 device, available from Porometer.com. Typically the Porolux™ 1000 is set at the maximum pressure (about 34 bar) and one measures the flow rate (L/min) of N2 gas through the porous substrate under test. The N2 flow rate through the porous substrate at a pressure of about 34 bar for an effective sample area of 2.69cm ² (effective diameter of 18.5mm) is preferably >1 L/min, more preferably >5L/min, especially >10L/min, more especially >25L/min. The higher of these flow rates are preferred because this reduces the likelihood of the gas flux of the resultant membrane being reduced by the porous substrate.

In contrast, when the porous substrate comprised a gutter layer (e.g. PTMSP or PDMS) the N2 gas flow rate of the porous substrate was much lower, typically below 1 L/min.

The GSMs of the present invention are very robust, have few surface defects and retain good selectivity for long periods of time. These properties are retained even when the GSMs are used to separate gases at very high pressure and temperature and when feed gas comprises H2S. In addition, the bond between the discriminating layer and the porous substrate is very strong and the GSM has good scratch resistance. Thus the GSMs of the present invention do not need a protective layer (PL) on top of the discriminating layer, although a PL may be included if desired.

The thickness of the various layers (e.g. the porous substrate, the discriminating layer and the optional (though not mandatory) protective layer) may be determined by cutting through the GSM and examining its cross section by SEM. The part of the discriminating layer which is present within the pores of the porous substrate is not taken into account when defining the thickness of the discriminating layer.

Preferably the GSM of the present invention has an average dry thickness (including the porous substrate) in the range 0.05 to 10pm, more preferably 0.09 to 5pm and especially 0.1 to 3pm.

Preferably the GSM of the present invention has a H2S/CH4 selectivity (aH2S/CH4) ^30. Preferably the selectivity is determined by a process comprising exposing the membrane to a CO2/CH4/nC4H /H2S = 47/33/0.5/0.1 (amounts by volume) of H2S and CH4 respectively at a feed pressure of 3760 kPa at 30°C.

Preferably the GSM of the present invention has a permeability to H2S of at least 300 Barren Preferably the GSM has a permeability to CH4 of at most 10 Barren The permeability may be measured by the method described below.

The GSM is preferably in tubular form or, more preferably, in sheet form. Tubular forms of GSMs are sometimes referred to as being of the hollow fibre type. GSMs in sheet form are suitable for use in, for example, spiral-wound, plate-and-frame and envelope cartridges.

While this specification emphasizes the usefulness of the GSMs of the present invention for separating gases, especially polar and non-polar gases, it will be understood that the GSMs can also be used for other purposes, for example providing a reducing gas for the direct reduction of iron ore in the steel production industry, dehydration of organic solvents (e.g. ethanol dehydration), pervaporation, oxygen enrichment, solvent resistant nanofiltration and vapor separation.

The GSMs of the present invention are particularly suitable for separating a feed gas containing a target gas into a gas stream rich in the target gas and a gas stream depleted in the target gas. For example, a feed gas comprising polar and non-polar gases may be separated into a gas stream rich in polar gases and a gas stream depleted in polar gases. In many cases the GSMs have a high permeability to polar gases, e.g. CO2, H2S, NH3, SO _X , and nitrogen oxides, especially NO _X , relative to nonpolar gases, e.g. alkanes, H2, N2, and water vapor.

The target gas may be, for example, a gas which has value to the user of the GSM and which the user wishes to collect. Alternatively the target gas may be an undesirable gas, e.g. a pollutant or ‘greenhouse gas’, which the user wishes to separate from a gas stream in order to meet product specification or to protect the environment.

Preferably the GSM has a H2S/CH4 selectivity (aFhS/CF ) ^30. Preferably the selectivity is determined by a process comprising exposing the GSM to a CO2/CH4/nC4H /H2S = 77/22/0.7/0.3 (amounts by volume) of H2S and CH4 respectively at a feed pressure of 6000kPa at 40°C.

Preferably the GSM has a permeability to H2S of at least 300 Barren Preferably the GSM has a permeability to CH4 of at most 10 Barren The permeability may be measured by the method described below.

Preferably the GSM is gas permeable and liquid impermeable.

According to a further aspect of the present invention there is provided a process for separating a feed gas comprising polar and non-polar gases into a gas stream rich in polar gases and a gas stream depleted in polar gases comprising bringing the feed gas into contact with a GSM according to the first aspect of the present invention.

Thus the GSMs of the present invention may be used for the separation of gases and/or for the purification of a gas According to another aspect of the present invention there is provided a gasseparation module comprising a GSM according to the first aspect of the present invention.

In the modules of the present invention the GSM is preferably in the form of a flat sheet, a spiral-wound sheet or takes the form of a hollow-fiber membrane. The invention will now be illustrated by the following non-limiting Examples in which all parts are by weight unless specified otherwise.

The following materials were used in the Examples (all without further purification):

V-601 is dimethyl 2,2'-azobis(2-methylpropionate) thermal initiator from

Wako Pure Chemical Industries Ltd. (this initiator can polymerise unsaturated monomers while NOT opening epoxy rings). n-BA is n-butyl acetate (an inert solvent from Sigma-Aldrich/Merck).

10591 is 4-isopropyl-4'-methyldiphenyliodonium Tetrakis(pentafluorophenyl) borate (an ring-opening adjuvant from TCI Chemicals ). (this initiator can polymerise unsaturated monomers and also open epoxy rings).

MeOH is methanol (an inert solvent).

GMA is glycidyl methacrylate (an epoxy monomer from Sigma-Aldrich).

M-PEG-A is methoxy polyethylene glycol) acrylate containing 13 sequential ethylene glycol units (a PEG monomer from Shin Nakamura Chemicals).

PEGDAA is poly(ethylene glycol) diacrylamide containing 12 sequential ethylene glycol units with NAMW of 600 Da (a crosslinking agent from Sigma-Aldrich). PEGDMAA i _s poly(ethylene glycol) dimethacrylamide containing 12 sequential ethylene glycol units with NAMW of 600 Da (a crosslinking agent from Sigma-Aldrich).

BYK is polyether modified acryl functional polydimethylsiloxane BYK UV-

3530 (an surfactant from BYK Chemie GmbH).

PEGDA i ^s poly(ethylene glycol) diacrylate containing 12 sequential ethylene glycol units with NAMW of 600 Da (a crosslinking agent from Sigma- Aldrich)

DMAPAA is N-[3-(dimethylamino)propyl]acrylamide (an acrylamide functionalizing agent from Sigma-Aldrich).

DMAPMAA ' ^S N-[3-(dimethylamino)propyl]methacrylamide (a methacrylamide functionalizing agent from Sigma-Aldrich). is trifluoroacetic acid (a catalyst for acrylamide functionalization from FA Sigma-Aldrich).

PAN i _{s a} polyacrylonitrile porous substrate (MN PAN an ultrafiltration membrane from MicrodynNadir) comprising a PET sheet backing material coated with PAN having a CO2 permeance 11 x 10’ ⁵ m ³ (STP)/m ² .s.kPa and a N2 gas flow of 2 L/min. is di(ethylene glycol)methyl ether methacrylate containing 2

DEGMEMA sequential ethylene glycol units (from Sigma-Aldrich). is methoxy poly(ethylene glycol) acrylate containing 4 sequential

M-PEG-A4 ethylene glycol units (from Sigma-Aldrich).

M-PEG-A13 ' ^{s me} thoxy polyethylene glycol) acrylate containing 13 sequential ethylene glycol units (AM130-G from Shin Nakamura).

M PEG All ' ^{S methoxy} P°ly(ethylene glycol) allyl ether containing 23 sequential ethylene glycol units (from Sigma-Aldrich).

M-PEG-MA is methoxy poly(ethylene glycol) methacrylate containing 9 sequential ethylene glycol units, purchased from Sigma-Aldrich. PEGDMA is poly(ethylene glycol) dimethacrylate containing 12 sequential ethylene glycol units with NAMW of 600 Da (a crosslinking agent from Sigma-Aldrich)

The performance of the GSMs of the present invention and Comparative GSMs were evaluated in the following tests:

Gas Selectivity and Permeability

The gas selectivity and permeability of each of the GSMs under test were measured using a feed gas having the composition CO2/CH4/nC4H /H2S in the ratio 47/33/0.5/0.1 (by volume). The feed gas was passed through each GSM under test at a temperature of 30°C and feed pressure of 3760kPa using a circular gas permeation cell having a measurement diameter of 1.5cm. The flow rate, pressure, and gas composition of each feed gas, permeate gas, and retentate gas was calculated according formulation described in “Calculation Methods for Multicomponent Gas Separation by Permeation” (Y. Shindo et al, Separation Science and Technology, Vol. 20, Iss. 5-6, 1985) with “countercurrent flow” mode.

Permeance (Q or Qi):

The permeability (Pi) of the GSMs was measured as follows:

The permeability (Pi) of the GSMs to CO2, H2S, CH4 and nC4H was determined using the following equation:

Pi ⁼ 0Perm' Xperm,i)/( ' Ppeed' Xpeed - Pperm' Xperm,i))

For example: wherein:

Pi = Permeability of the relevant gas (i.e. is CO2, H2S, CH4 or nC4H ) (m ³ (STP) m/m ² kPa s);

0Perm = Permeate flow rate (m ³ (STP)/s);

Xperm,i = Volume fraction of the relevant gas in the permeate gas;

A = Membrane area (m ² );

Ppeed = Feed gas pressure (kPa);

Xpeed,i = Volume fraction of the relevant gas in the feed gas;

Pperm = Permeate gas pressure (kPa); and

STP is standard temperature and pressure, which is defined here as 25.0°C and 1 atmosphere pressure (101 ,325kPa). The Barrer (P) was then determined by 1 Barrer = 1 x10’ ¹⁰ cm ³ (STP) cm/(s • cm ² • cmHg).

The permeance (Q) results shown in Table D1 were calculated from the permeability (Pi) as follows:

The permeance (Q or Qi when referring to a specific gas) of the GSMs to H2S, CO2, CH4 and nC4H was determined using the following equation: Qi = Pi L

Qi = Permeance of the relevant gas (i is CO2, H2S, CH4 or nC4H ) (m ³ (STP)/m ² kPa s);

L = Thickness of discriminating layer in membrane [pm]

The permeance (Q) was then determined by 1 GPU = 1 x10’ ⁶ cm ³ (STP)/(s • cm ² • cmHg).

The resultant H2S permeances Q(H2S) are shown in Table D1.

Selectivity ad-hS/CI-k)

The selectivity results (a(H2S/CH4)) shown in Table D1 were measured as follows:

The membrane patch selectivity (H2S/CH4 selectivity; a(H2S/CH4)) of the membrane under test for the gas mixture was calculated respectively from P(H2S) and P(CH4) calculated as described in the formulas above based on following equations:

H2S/CH4 selectivity a(H2S/CH4)= P(H2S)/P(CH4)

Dying Test for Defects in the Discriminating Layer

Defects in the discriminating layer (DL) of the GSMs under test were identified as follows: 6 drops of a dye solution ((a 1wt% solution of 1 ,4-bis[(2-ethylhexyl)amino]- anthraquinone (solvent blue) in n-heptane) were applied to the DL at room temperature and left in contact with the DL for 30 seconds. Then the excess of dye solution was removed from the DL and the DL was washed with n-heptane. The DL was then examined visually with the naked eye. If blue spots were visible on the DL this indicated the presence of defects (e.g. pinholes) and the GSM was scored "Defect" (which is not OK). If no blue spots were visible this indicated the absence of defects and the GSM was scored "okay" (abbreviated to OK).

The results of the dying test are shown in Table D1 below. Determination of the Value of Mw, MANW and (m+n):

The value of (m+n) in the DL of GSMs prepared in the Examples was determined as follows:

Each GSMs (12.57 cm ² ) comprising a DL was placed in 2.0 M HCI solution (aq.) for 16 hours. The solution was analysed for its polyacrylic acid content (arising from hydrolysis of the DL) by gel permeation chromatography (GPC, Waters) and liquid chromatography mass spectrometry (LC-MS, Waters). The presence of polyacrylic acid was determined from LC-MS analysis, and the Mw and NAMW were determined from GPC analysis, of which the value of (m+n) could be determined by dividing the obtained Mw by the molecular weight of acrylic acid (72.06 g/mol). The GPC system used was a Viscotek TDA 305 GPC coupled to a Viscotek VE 2001 GPC solvent/sample module.

The Mw and NMAW for the polymers were determined by diluting 1 g of each polymer ((C)CGPs or (C)EPs) up to 250 g with THF (tetrahydrofuran for HPLC (>99,9% inhibitor free)) from Sigma Aldrich/Merck in duplicate.

Both solutions were subjected to GPC analysis with the same THF as eluent at 60 degrees Celsius to obtain the NAMW molecular weight distribution of the polymers. The GPC system used was a Viscotek TDA 305 GPC coupled to a Viscotek VE 2001 GPC solvent/sample module.

The Mw and NAMW of each epoxy polymer is shown in Table A2 below.

Polydispersity (PD) of the Epoxy Polymers

The PD of each epoxy polymer was determined by measuring its Mw and NAMW by GPC and dividing the Mw by the NAMW. The GPC analysis was performed using THF as an eluent and M-PEG-A as a reference for the calibration and calculation of the weight-average molecular weight (Mw) and NAMW.

The PD of each epoxy polymer is shown in Table A2 below.

Determination of the Value of q for the Epoxy Polymers

The value of q for each epoxy polymer was determined by LC-MS analysis and is shown in Table A2 below.

Composition chains of matrix polymer

A preferred technique to analyze the components (including its EO-content, main chain and side chain polymer) of the discriminating layer of the GSM can be done by combination of surface chemical analysis e.g. FTIR, TOF-SIMS, etc., with decomposition chemical analysis through hydrolyzation of the discriminating layer with high or low pH solution (caustic soda, nitric acid, etc) and analyze the hydrolysis product by size-exclusion chromatography, NMR, HPLC-MS, GPC-MS, mass spectrometry. EO content determination on GSMs

12.57cm ² of GSMs under test were degraded in 10 ml 1 M NaOD sodium deuteroxide (40wt% in deuterium oxide, 99,5 atom% D in deuterated water solution) from Sigma Aldrich/Merck in deuterated water by heating the solutions to 60 degrees Celsius for 16 hours. The degraded solutions were diluted up to 20ml with deuterated water (D2O) (deuterated water, 99,9% atom% D) from Sigma Aldrich/Merck containing 1 wt% of calcium formate as internal standard. 1 H-NMR analysis using the signal of calcium formate (singlet at 8.30 ppm) was correlated to the signal of ethylene oxide (singlet at 3.5 ppm) and the EO content was quantified in duplicate. The 1 H- NMR spectra were recorded using a Magritek Spinsolve 60 MHz table-top NMR (32 scans, 90o pulse angle, 3 sec acquisition time, 30 sec relaxation time).

Examples

(a) Preparation of Epoxy Polymers (EPs and CEPs)

Compositions EP1 to EP10 and CEP1 to CEP6 were prepared as follows: the monomers and the inert solvents indicated in Table A1 below were mixed at room temperature while purging with nitrogen gas for 1 hour. The resultant mixture was warmed to 70°C and then the initiator indicated in Table A1 was added as a 1wt% solution in MeOH. The mixture was stirred at 70°C for 16 hours and then cooled down to room temperature to give the desired (C)EP (= acrylic copolymer). The value of (m+n), Mw, Mn, and PD for the resultant (C)EPs were measured using the methods described above and the results are shown in Table A2.

Table A1 : Preparation of Epoxy Polymers*

* The sum of all wt% relative to the total composition + wt% of MeOH sum up to 100%.

Notes on Table A1 : 1 ) Example 11 provided an epoxy polymer comprising a (meth)acrylic copolymer backbone having in-chain amide links (derived from PEGDMAA).

2) Examples 12 and 13 (CEP1 and CEP2) did not contain epoxy groups and therefore the resultant polymers were unable to form pendent (meth)acrylamide groups on the (meth)acrylic copolymer backbone in the subsequent stages described below.

3) Examples 14, 15 and 16 provided epoxy polymers having a NAMW below 350KDa.

Table A2: Analysis Results Obtained from the Epoxy Polymers described in Table A1

Note: CEP1 and CEP2 did not actually contain epoxy groups (Comparative). b) Preparation of Curable Copolymers and Comparative Polymers by Reaction of the Epoxy Polymers with a (meth)acrylamide compound

The epoxy polymers EP1 to EP11 and comparative polymers CEP1 to CEP5 were treated with a(n) (meth)acrylamide functionality as indicated in Table B1 below. The compositions from step a) (described above) were each mixed with DMAP(M)AA (32.33 mol% vs polymer) and trifluoroacetic acid (1.0 equiv.) was then added to catalyse reaction of any epoxy groups in the epoxy polymer with the DMAP(M)AA in order to form, where possible, curable copolymers comprising a backbone derived from the epoxy polymer and pendent side chains derived from the DMAP(M)AA. Subsequently the mixture of epoxy polymer, DMAP(M)AA and trifluoracetic acid was heated to 60 °C while stirring for overnight. The resultant mixture was cooled down to room temperature and used directly(as a mixture) to make discriminating layers as described below.

Table B1 : Preparation of Curable Copolymers and Comparative Polymers

Notes:

1 ) The polymers in CCGP1 and CCGP2 did not comprise pendent (meth)acrylamide groups (therefore Comparative).

2) The EO content of the polymers in CCGP4 and CCGP5 was very low and therefore these curable polymers were unable to form discriminating layers having the EO content required by claim 1 (therefore Comparative).

3) The curable polymers in compositions CCPG3, CCPG4 and CCCPG5 had a NAMW of less than 350kDa (therefore Comparative).

(c) Preparation of Compositions used to form the Discriminating Layer

Each of the polymer solutions resulting from step (b) (listed in the final column of Table B1 above and used without purification or separation from the reaction mixture it was prepared from) was formulated into a composition comprising that polymer solution (10wt%), MEK (89.3wt%), BYK (0.5wt%) and Omnirad 1173 (0.2wt%) and the resultant compositions were stirred for at least 15 minutes to obtain a homogeneous mixture. This gave compositions DL1 to DL12 (derived from CGP1 to CGP12 respectively) and comparative compositions CDL1 to CDL5 (derived from CCGP1 to CCGP5 respectively) which were then used in step (d) below to prepare GSMs.

(d) Preparation of GSMs using Ex1 -Ex12 and CEx1 -CEx5

Compositions DL1 to DL12 and comparative compositions CDL1 to CDL5 from step (c) above were coated onto a porous substrate (PAN) as indicated in Table C1 below The coating was performed continuously and at 20°C, onto the porous substrate (PAN) using just one slot of a slide bead coating machine. The resultant, coated porous substrates were then cured by passing them under an irradiation source (a Light Hammer LH6 from Fusion UV Systems fitted with a H-bulb working at 100% intensity) and then to a drying zone at 60°C. The resultant dried, GSMs were then transported to a collecting station. The thickness of the discriminating layer in each GSM (as shown in Table C1 ) was determined by cutting through the GSM and measuring the thickness of the discriminating above the porous substrate using a scanning electron microscope (SEM).

Table C1 :

In Table C1 : Y means yes and N means No.

(e) Testing of the GSMs

The GSMs obtained in step (d) above were tested using the methods described above to determine their H2S permeance (Q(H2S)) and their H2S/CH4 selectivity (a(H2S/CH4)). The results are shown in Table D1 below. A H2S permeance (Q(H2S)) above 150 GPU was deemed to be good. A H2S/CH4 selectivity (a(H2S/CH4)) of at least 30 was deemed to be good. The DL of the GSMs were inspected for defects using the dying test described above.

From Table D1 it can be seen that the GSMs according to the present invention have good H2S permeance (>150 GPU) and very good H2S/CH4 selectivity (^30). Table D1 - Results

ND = cannot be determined as GSM is leak, no separation possible for H2S versus CH ₄ .