WO2019165597A1 - Functionalized polyimides and membranes for gas separations - Google Patents

Functionalized polyimides and membranes for gas separations Download PDF

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WO2019165597A1
WO2019165597A1 PCT/CN2018/077544 CN2018077544W WO2019165597A1 WO 2019165597 A1 WO2019165597 A1 WO 2019165597A1 CN 2018077544 W CN2018077544 W CN 2018077544W WO 2019165597 A1 WO2019165597 A1 WO 2019165597A1
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mol
group
independently
polyimide
monomer units
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PCT/CN2018/077544
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French (fr)
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Jianhua Fang
Rui Liu
Jinhua JIANG
Jing Feng
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Evonik (Shanghai) Investment Management Co., Ltd.
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Priority to CN201880090336.8A priority Critical patent/CN111918712A/en
Priority to PCT/CN2018/077544 priority patent/WO2019165597A1/en
Publication of WO2019165597A1 publication Critical patent/WO2019165597A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/22—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
    • B01D53/228—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion characterised by specific membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/58—Other polymers having nitrogen in the main chain, with or without oxygen or carbon only
    • B01D71/62—Polycondensates having nitrogen-containing heterocyclic rings in the main chain
    • B01D71/64—Polyimides; Polyamide-imides; Polyester-imides; Polyamide acids or similar polyimide precursors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2256/00—Main component in the product gas stream after treatment
    • B01D2256/10—Nitrogen
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2256/00—Main component in the product gas stream after treatment
    • B01D2256/24—Hydrocarbons
    • B01D2256/245—Methane
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/10—Single element gases other than halogens
    • B01D2257/104—Oxygen
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/50—Carbon oxides
    • B01D2257/504—Carbon dioxide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/76—Macromolecular material not specifically provided for in a single one of groups B01D71/08 - B01D71/74
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/40—Capture or disposal of greenhouse gases of CO2

Definitions

  • the present invention relates to a functionalized polyimide, a high performance polyimide membrane for gas separations and a versatile process for chemical modification of aromatic polyimides.
  • Polymer membranes are applied in gas separations, as they allow separation of gases with low energy consumption and without use of absorbents.
  • the performance of a polymer membrane in a gas separation process depends both on the gas permeability of the membrane and the permeation selectivity for the components of a gas mixture.
  • permeability and selectivity there is a trade-off relation between permeability and selectivity, as membranes having high permeability usually have low selectivity and vice versa (L.M. Robeson, J. Membrane Sci. 320 (2008) 390-400) . It is very difficult to further improve membrane gas separation performance (to break Robeson’s upper-bound line) .
  • Polyimides are useful for making polymeric gas separation membranes, as they can provide both high mechanical stability, which allows their use at high gas pressures, as well as a combination of permeability and selectivity close to the Robeson upper boundary to membrane performance.
  • the properties of polyimide gas separation membranes are usually tailored by choice of the dianhydride and diamine building blocks of the polyimide and by use of mixtures of dianhydride and diamine building blocks, i.e. by modifying the monomers used to make the polyimide.
  • K. Okamoto et al., Polym. J. 30 (1998) 492-498 describes functionalizing a polyimide prepared from 3, 3’, 4, 4’-biphenyltetracarboxylic dianhydride (BPDA) and 2, 4, 6-trimethyl-1, 3-phenylenediamine (TrMPD) by brominating benzylic methyl groups and reacting the resulting benzylic bromide groups with trimethyl phosphite or triethyl phosphite to provide a polyimide functionalized with phosphonate ester groups.
  • the functionalized polymer was crosslinked by heating or by reaction with 1, 2-diaminoethane.
  • the functionalized and crosslinked polymer provided improved selectivity without reduction of permeation flux when used for separating a mixture of benzene and cyclohexane by pervaporation.
  • JPH 9-173801 describes a method for preparing gas separation membranes by brominating alkyl groups of an alkyl substituted polyimide, preparing a film from the resulting brominated polyimide and treating the brominated polyimide film with vapor or an aqueous solution of ammonia, a primary amine or a secondary amine.
  • An alternative method is described in paragraph [0023] , where the brominated polyimide is reacted with a secondary amine, such as diethanol amine or morpholine, in solution to provide an amine-modified polyimide, followed by preparing the membrane by coating or casting a solution of the amine-modified polyimide on a substrate.
  • the amine-modified polyimide membranes show an increase in selectivity compared to the non-modified polyimide membranes in gas separation, but permeability is considerably decreased.
  • the objective of this invention is to develop a versatile approach by which polyimide membranes with both significantly enhanced gas permeability coefficients and good selectivities at the same time can be produced.
  • imide functionalized polyimides can be prepared by brominating an aromatic polyimide comprising benzylic groups and reacting the resulting brominated polyimide with a cyclic imide salt, preferably an alkali metal salt of a cyclic imide.
  • a cyclic imide salt preferably an alkali metal salt of a cyclic imide.
  • gas separation membranes prepared from such an imide functionalized polyimide can provide both better selectivity and good permeability for separating a gas mixture, compared with the pristine polyimide.
  • a subject of the invention is therefore a method for preparing a functionalized polyimide, comprising the steps of
  • each R A independently of one another, is an aromatic dianhydride monomer unit
  • each R B independently of one another, is an aromatic diamine monomer unit, and at least part of said aromatic diamine monomer units R B comprise one or more methyl groups on the aromatic ring;
  • step b) reacting the solution of step a) with a brominating agent and an initiator or photoinitiation to convert at least part of said methyl groups to bromomethylene groups, providing a brominated polyimide, preferably the degree of bromination is 20%-150%, for example 20%-140%, 20%-140%, 20%-130%, more preferably 20%-120%, even more preferably 30%-75%;
  • step d) reacting the solution of step c) with a cyclic imide salt to convert at least part of the bromomethylene groups to imidomethylene groups.
  • the imidomethylene groups are formed by reacting the imido anion groups of the cyclic imide salt with the bromomethylene groups of the brominated polyimide.
  • At least 5 mol-%, preferably at least 10 mol-%, for example, from 5 to 100 mol-%, 10 to 100 mol-%, 10 to 99 mol-%, 10 to 95 mol-%, 10 to 90 mol-%, 10 to 85 mol-%, 10 to 80 mol-%, 20 to 100 mol-%, 20 to 99 mol-%, 20 to 95 mol-%, 20 to 90 mol-%, 20 to 85 mol-%, 20 to 80 mol-%, 30 to 100 mol-%, 30 to 99 mol-%, 30 to 95 mol-%, 30 to 90 mol-%, 30 to 85 mol-%, 30 to 80 mol-%of bromomethylene groups are converted to imidomethylene groups in step d) .
  • the polyimide of step a) may be used to prepare gas separation membranes.
  • the gas separation membranes prepared from the polyimide of step a) have lower gas separation efficiency.
  • the degree of bromination may be determined according to conventional methods such as elemental analysis and/or 1 H NMR spectra, typically elemental analysis.
  • the mol-%of bromomethylene groups converted to imidomethylene groups may be determined according to the method of elemental analysis.
  • a cyclic imide is an imide comprising two acyl groups bound to a nitrogen atom, in which the two carbonyl carbons are connected by a substituted or non-substituted carbon chain or substituted or non-substituted aromatic group.
  • a cyclic imide salt is a tertiary amine salt formed by said cyclic imide.
  • the cyclic imide salt is preferably a cyclic imide alkaline metal salt, more preferably a cyclic imide potassium or sodium salt.
  • the cyclic imide salt may have the following general structure (II) :
  • each R 1 to R 6 independently of each other being hydrogen, or a C 1 to C 4 alkyl group unsubstituted or substituted by one or more halogen groups such as fluoro-, chloro-and bromo-group; the C 1 to C 4 alkyl group is preferably selected from –CH 3 , -CF 3 , -CH (CH 3 ) 2 , and –C (CH 3 ) 3 ; and
  • M + represents a metal ion, preferably an alkaline metal ion, especially K + or Na + .
  • the cyclic imide salt comprises a naphthalene ring
  • it is preferably unsubstituted on the naphthalene ring.
  • the cyclic imide salt comprises a benzene ring
  • it preferably comprises no or only one alkyl substituent group on the benzene ring.
  • cyclic imide salt may be selected from an alkali metal ⁇ -methyl- ⁇ -phenylsuccinimide salt, an alkali metal succinimide salt, an alkali metal phthalimide salt or an alkali metal salt of naphthalene 1, 8-dicarboxylic acid imide.
  • the functionalized polyimide including the functionalized polyimide obtainable by this method, a gas separation membrane comprising the functionalized polyimide of the invention, a gas separation device comprising the gas separation membrane of the invention and a method for separating a gas mixture comprising contacting the mixture with the gas separation membrane of the invention and applying a pressure difference across the gas separation membrane to effect permeation of at least one component of the gas mixture through the gas separation membrane.
  • the polyimide may be a polymer of structure (III)
  • aromatic dianhydride monomer units R A independently of one another, are selected from the group consisting of:
  • aromatic diamine monomer units R B1 independently of one another, are selected from the group consisting of:
  • each R 1 to R 7 independently of each other being hydrogen or a methyl group with the proviso that at least one of R 1 to R 3 is different from hydrogen, and at least one of R 4 to R 7 is different from hydrogen;
  • R 8 being hydrogen or a C 1 to C 3 alkyl group unsubstituted or substituted by one or more halogen groups such as fluoro-, chloro-and bromo-group, preferably hydrogen or methyl;
  • aromatic diamine monomer units R B2 independently of one another, are selected from the group consisting of:
  • x is from 0.1 to 1, for example 0.15 to 1, 0.2 to 1, 0.25 to 1, 0.3 to 1, 0.35 to 1, 0.4 to 1, 0.45 to 1, 0.5 to 1, 0.55 to 1, 0.6 to 1, 0.65 to 1, 0.7 to 1, 0.75 to 1, 0.8 to 1, 0.85 to 1, 0.9 to 1, 0.95 to 1.
  • the aromatic diamine monomer units R B1 are selected from the group consisting of:
  • the aromatic diamine monomer units R B1 are selected from the group consisting of:
  • the aromatic dianhydride monomer units R A are selected from the group consisting of:
  • the polyimide is a polymer, especially a block copolymer of structure (IV)
  • aromatic dianhydride monomer units R A1 independently of one another, are selected from the group consisting of:
  • aromatic diamine monomer units R B3 independently of one another, are selected from the group consisting of:
  • aromatic dianhydride monomer units R A2 independently of one another, are selected from the group consisting of:
  • aromatic diamine monomer units R B4 independently of one another, are selected from the group consisting of:
  • each R 1 to R 7 independently of each other being hydrogen or a methyl group; R 8 being as stated above;
  • y is from 5 to 500
  • z is from 5 to 500
  • R A1 is different from R A2
  • R B3 is different from R B4 or both R A1 is different from R A2 and R B3 is different from R B4 .
  • R B4 of the polyimide above is selected from the group consisting of:
  • the term “functionalized polyimide” refers to the polyimide after functionalizing the brominated polyimide with the cyclic imide salt, unless otherwise explicitly specified.
  • the invention provides a technical approach for producing functionalized polyimides with significantly improved gas separation performance. It involves bromination of the polyimides derived from methyl-substituted diamines in the first step and functionalization with a cyclic imide salt in the next step.
  • the bromination reaction can be performed by heating a solution mixture containing a polyimide, a brominating reagent and an initiator or photoinitiation.
  • the methylene bromide groups of the resulting brominated polyimide undergo a next step functionalization with the cyclic imide salt to give the desired product.
  • the pristine polyimides are polyimides with repeat units (I) , preferably polymer of structure (III) .
  • the method to prepare a functionalized polyimide comprises the following steps:
  • the reaction of step b) is conducted at 60-120°C for 0.5-24 hrs, preferably 70-100 °C for 2-10 hrs.
  • the reaction of step d) is conducted at 30-120 °C for 1-60 hrs, for example 2-60 hrs, 2-48 hrs, 2-36 hrs, 2-24hrs or 1-24 hrs.
  • the molar ratio between the brominated polyimide and the cyclic imide salt is 1: 0.05 to 1: 5, preferably 1: 0.1 to 1: 2.
  • the reaction product obtained in step (a) is cooled to room temperature, then the solution mixture is poured in to a nonsoluble organic liquid (non-solvent) such as methanol, the resulting precipitate is collected by filtration, thoroughly washed with the nonsoluble organic liquid and dried in vacuum to yield the brominated polyimide.
  • a nonsoluble organic liquid such as methanol
  • the reaction product obtained in step (b) is cooled to room temperature, then the solution mixture is poured into a nonsoluble organic liquid such as methanol and the resulting precipitate is collected by filtration, thoroughly washed with deionized water, and dried in a vacuum oven to yield the functionalized polyimide.
  • a nonsoluble organic liquid such as methanol
  • the methyl groups of the above mentioned polyimides can be readily brominated by reacting with a conventional brominating reagent such as N-bromosuccinimide (NBS) , dibromoisocyanuric acid and 1, 3-dibromo-5, 5-dimethyl hydantoin in the presence of an initiator such as benzoyl peroxide (BPO) .
  • NBS N-bromosuccinimide
  • BPO benzoyl peroxide
  • organic solvents such as 1, 1, 2, 2-tetrachloroethane (TCE) , chloroform, methylene dichloride, N, N-dimethylforamide (DMF) , N, N-dimethylacetamide (DMAc) and 1-methylpyrrolidinone (NMP) can be used for dissolving the polyimides depending on their individual chemical structures.
  • TCE 1, 1, 2, 2-tetrachloroethane
  • DMF N-dimethylforamide
  • DMAc N-dimethylacetamide
  • NMP 1-methylpyrrolidinone
  • N-bromosuccinimide N-bromosuccinimide
  • TCE 1, 1, 2, 2-tetrachloroethane
  • DMF N, N-dimethylforamide
  • the bromination reaction is carried out at 70-100 °C for 2-10 hrs.
  • the above brominated polyimide can be dissolved in a conventional solvent such as dichloromethane, chloroform, 1, 1, 2, 2-tetrachloroethane (TCE) , N, N-dimethylforamide (DMF) , N, N-dimethylacetamide (DMAc) and 1-methylpyrrolidinone (NMP) , etc. to give a 1-30 w/v%solution.
  • a cyclic imide salt such as potassium phthalimide,
  • the solution mixture can be poured into a nonsoluble organic liquid such as methanol and the resulting precipitate can be collected by filtration, thoroughly washed with deionized water, and dried in a vacuum oven.
  • phthalimide potassium salt and naphthalimide potassium salt are selected to react with the brominated polyimides, for example at 40 °C for 24 hrs.
  • the brominating agent is selected from N-bromosuccinimide, dibromoisocyanuric acid and 1, 3-dibromo-5, 5-dimethyl hydantoin.
  • the photoinitiation is by irradiation with UV light.
  • the initiator is used by addition of an organic peroxide and heating.
  • the organic peroxide is a dialkylperoxide, an alkyl acyl peroxide or a diacylperoxide, preferably a diacylperoxide, more preferably dibenzoylperoxide.
  • the molar ratio of brominating agent to the benzylic groups of said aromatic diamine monomer units R B is from 0.05 to 1.
  • step b) is carried out in a chlorohydrocarbon solution, preferably in a 1, 1, 2, 2-tetrachloroethane solution.
  • step b) is carried out in a carboxylic acid dialkylamide solution, preferably a solution in N, N-dimethylformamide, N, N-dimethylacetamide or N-methylpyrolidone.
  • the cyclic imide salt is an alkali metal cyclic imide salt.
  • the alkali metal cyclic imide salt is selected from an alkali metal ⁇ -methyl- ⁇ -phenylsuccinimide salt, an alkali metal succinimide salt, an alkali metal phthalimide salt or an alkali metal salt of naphthalene 1, 8-dicarboxylic acid imide.
  • step d) is carried out in a carboxylic acid dialkylamide solution, preferably a solution in N, N-dimethylformamide, N, N-dimethylacetamide or N-methylpyrolidone.
  • step d) is carried out at a temperature of from 30 to 120 °C.
  • step b) the brominating agent is N-bromosuccinimide or dibromoisocyanuric acid and steps c) and d) are carried out by adding an alkali metal alkoxide to the solution obtained in step b) in an amount sufficient for converting the succinimide or phthalimide formed in step b) into the alkali metal succinimide salt or alkali metal phthalimide salt.
  • a further subject of the invention is a functionalized polyimide, obtainable by a method according to the present invention.
  • a further subject of the invention is a functionalized polyimide, wherein the polyimide is a polymer, including a random copolymer of structure (III)
  • aromatic dianhydride monomer units R A independently of one another, are selected from the group consisting of:
  • aromatic diamine monomer units R B1 independently of one another, are selected from the group consisting of:
  • each R 1 to R 7 independently of each other being hydrogen or a group R c with the proviso that at least one of R 1 to R 3 is different from hydrogen, and at least one of R 4 to R 7 is different from hydrogen,
  • R 8 being hydrogen or a C 1 to C 3 alkyl group unsubstituted or substituted by one or more halogen groups such as fluoro-, chloro-and bromo-group, preferably hydrogen or methyl,
  • R c being methyl or a CH 2 R d group with the proviso that at least 5 mol-%, for example at least 10 mol-%, at least 15 mol-%, at least 20 mol-%, at least 25 mol-%, at least 30 mol-%, at least 35 mol-%, at least 40 mol-%, at least 45 mol-%, at least 50 mol-%, at least 55 mol-%, at least 60 mol-%, at least 65 mol-%, at least 70 mol-%, at least 75 mol-%, at least 80 mol-%, at least 85 mol-%, at least 90 mol-%of groups
  • R c are CH 2 R d groups, for example from 5 to 100 mol-%, 10 to 100 mol-%, 10 to 99 mol-%, 10 to 95 mol-%, 10 to 90 mol-%, 10 to 85 mol-%, 10 to 80 mol-%, 10 to 75 mol-%, 10 to 70 mol-
  • R d being structure (II’) :
  • each R 1 to R 6 independently of each other being hydrogen, or a C 1 to C 4 alkyl group unsubstituted or substituted by one or more halogen groups such as fluoro-, chloro-and bromo-group; the C 1 to C 4 alkyl group is preferably selected from –CH 3 , -CF 3 , -CH (CH 3 ) 2 , and –C (CH 3 ) 3 ;
  • aromatic diamine monomer units R B2 independently of one another, are selected from the group consisting of:
  • x is from 0.1 to 1, for example 0.15 to 1, 0.2 to 1, 0.25 to 1, 0.3 to 1, 0.35 to 1, 0.4 to 1, 0.45 to 1, 0.5 to 1, 0.55 to 1, 0.6 to 1, 0.65 to 1, 0.7 to 1, 0.75 to 1, 0.8 to 1, 0.85 to 1, 0.9 to 1, 0.95 to 1.
  • the unfunctionalized polyimide is the polyimide of structure (III) but has R c being all methyl.
  • the unfunctionalized polyimide is functionalized by R d group on at least part of the methyl groups.
  • Such unfunctionalized polyimide may also be used to prepare gas separation membranes.
  • the gas separation membranes prepared from such unfunctionalized polyimide have lower gas separation efficiency.
  • each R 1 to R 7 in the aromatic diamine monomer unit R B1 of the functionalized polyimide above is a group R c .
  • x is 1 and the aromatic diamine monomer units R B1 , independently of one another, are selected from the group consisting of:
  • the aromatic dianhydride monomer units R A are selected from the group consisting of:
  • the polyimide is a polymer, including a block copolymer of structure (IV)
  • aromatic dianhydride monomer units R A1 independently of one another, are selected from the group consisting of:
  • aromatic diamine monomer units R B3 independently of one another, are selected from the group consisting of:
  • R c being methyl or a CH 2 R d group with the proviso that at least 5 mol-%, for example at least 10 mol-%, at least 15 mol-%, at least 20 mol-%, at least 25 mol-%, at least 30 mol-%, at least 35 mol-%, at least 40 mol-%, at least 45 mol-%, at least 50 mol-%, at least 55 mol-%, at least 60 mol-%, at least 65 mol-%, at least 70 mol-%, at least 75 mol-%, at least 80 mol-%, at least 85 mol-%, at least 90 mol-%of groups
  • R c are CH 2 R d groups, for example from 5 to 100 mol-%, 10 to 100 mol-%, 10 to 99 mol-%, 10 to 95 mol-%, 10 to 90 mol-%, 10 to 85 mol-%, 10 to 80 mol-%, 10 to 75 mol-%, 10 to 70 mol-
  • R d being structure (II’) :
  • each R 1 to R 6 independently of each other being hydrogen, or a C 1 to C 4 alkyl group unsubstituted or substituted by one or more halogen groups such as fluoro group; the C 1 to C 4 alkyl group is preferably selected from –CH 3 , -CF 3 , -CH (CH 3 ) 2 , and –C (CH 3 ) 3 ;
  • aromatic dianhydride monomer units R A2 independently of one another, are selected from the group consisting of:
  • aromatic diamine monomer units R B4 independently of one another, are selected from the group consisting of:
  • each R 1 to R 7 independently of each other being hydrogen or a group R c as defined above; R 8 being as defined above;
  • y is from 5 to 500
  • z is from 5 to 500
  • R A1 is different from R A2
  • R B3 is different from R B4 or both R A1 is different from R A2 and R B3 is different from R B4 .
  • R B4 is selected from the group consisting of:
  • the polyimide polymer of the invention may be either homopolymer or copolymer.
  • the type of copolymer is not limited, for example, the copolymer may be alternating copolymer, periodic copolymer, statistical copolymer, block copolymer etc.
  • the functionalized polyimide of the invention is suitable to prepare a gas separation membrane.
  • a further subject of the invention is a gas separation membrane, comprising a functionalized polyimide of the present invention.
  • the membrane is prepared from the functionalized polyimide of the present invention.
  • the membrane is asymmetrical with a non-porous polyimide film on a porous layer.
  • the membrane has the shape of a hollow fibre.
  • a further subject of the invention is method for separating a gas mixture, comprising contacting the mixture with a gas separation membrane according to the present invention and applying a pressure difference across the gas separation membrane to effect permeation of at least one component of the gas mixture through the gas separation membrane.
  • a further subject of the invention is a gas separation device, comprising the gas separation membrane of the present invention.
  • the functionalized polyimide membranes of this invention exhibited both significantly enhanced gas permeability coefficients and good selectivities at the same time.
  • Membranes can be fabricated by conventional methods. For example, membranes can be fabricated by solution cast method with a 2-25 w/v%polymer solution.
  • Gas permeability coefficient is closely dependent on polymer fractional free volume (V F ) and the higher V F , the higher permeability coefficient.
  • V F polymer fractional free volume
  • selectivity is closely related to the interaction between polymer segments and penetrant gas molecules.
  • a polymeric membrane with high affinity for one kind of penetrant but little affinity for another penetrant tends to has high selectivity.
  • the modified polyimides exhibited greatly enhanced affinity for gases such as CO 2 and O 2 but little affinity for gases such as N 2 and CH 4 leading to higher or similar selectivity.
  • the membranes made by the functionalized polyimide of the invention is especially suitable for separation of gases for example CO 2 /N 2 , CO 2 /CH 4 , O 2 /N 2 .
  • the invention grafts highly polar and bulky functional groups into polyimide backbone via proper chemical modifications (bromination and functionalization) and results in greatly enhanced gas permeability coefficients and enhanced selectivities at the same time.
  • the method of the invention is applicable to a broad range of polyimides of which structure contains methyl groups in the diamine moieties (polyimides derived from methyl-substituted diamines) .
  • the reaction conditions are moderate and easy to control.
  • Figure 1 shows the Fourier transform infrared (FT-IR) spectroscopy analysis result of the functionalized polyimide obtained in Example 4.
  • the tensile strength was determined with a universal tensile machine (Instron 4465, commercially available from Instron Co. Ltd., U.S.A. ) .
  • the samples were 80 mm long, 5 mm wide and 30-50 ⁇ m thick.
  • the cross-head rate was 2 mm/min.
  • the gas permeability was determined with a gas solubility and diffusivity test machine GTR-1ADFE (commercially available from GTR Tec Corporation, Japan) .
  • the test was performed at an upstream pressure of 0.1-0.4 MPa at 35 °C.
  • the measurement was based on a vacuum time-lag method and the gas permeability coefficient (P) was determined from a steady state permeation flux in a period between 5 and 10 times the time lag ( ⁇ ) .
  • the effective membrane area was 15.2 cm 2 .
  • the degree of bromination was determined by elemental analysis using an elemental analyzer (Vario EL Cube, Germany) .
  • the mol-%of bromomethylene groups converted to imidomethylene groups was also determined according to the method of elemental analysis.
  • the FT-IR was recorded on a Paragon 1000PC FT-IR spectrometer (Perkin Elmer, Inc., USA) using a polyimide film.
  • Example 1 preparation of polyimide BPDA-TrMPD
  • the reaction mixture was further heated to 180 °C and kept at this temperature for 10 hrs. After cooling to room temperature, the highly viscous solution was poured into methanol and fiber-like precipitate was collected by filtration and finally dried in a vacuum oven at 120 °C for 10 hrs.
  • the polyimide product was denoted as BPDA-TrMPD.
  • the produced brominated polyimide was denoted as PI-0.7Br, here “0.7” refers to the molar ratio of NBS to BPDA-TrMPD in feed. From the elemental analysis data, the degree of bromination of this polyimide was calculated to be 59%. It exhibited a tensile strength of 72 MPa and an elongation at break of 87%.
  • the conversion degree (mol-%of bromomethylene groups converted to imidomethylene groups) was calculated to be 44%based on carbon and 48%based on other atoms (Br + O) .
  • Example 5 gas permeability coefficient and selectivity tests
  • a 5 w/v%polymer solution in an organic solvent (TCE or NMP) was cast onto glass plates and dried in an air oven at 60°C (for TCE) or 80 °C (for NMP) for 8 h.
  • the as-cast membranes were peeled from the glass plates and further dried at 120 °C for 12 h in vacuo.
  • Example 6 gas permeability coefficient and selectivity tests
  • the gas permeability coefficients and ideal selectivities of the phthalimide potassium salt-modified polyimide membrane (see Example 4) at 35 °C and 100 kPa (upstream pressure) were determined and illustrated in Table 3.
  • Table 3 the relevant data of the PI-0.7Br and the pristine polyimide (BPDA-TrMPD) membranes are also shown in this table. It is obvious that in comparison with the precursor membranes the phthalimide-potassium-salt-modified polyimide membrane exhibited both significantly enhanced gas permeability coefficients and enhanced selectivities.

Abstract

A functionalized polyimide prepared by brominating an aromatic polyimide and reacting the resulting brominated polyimide with a cyclic imide salt, a gas separation membrane comprising the functionalized polyimide of the invention, a gas separation device comprising the gas separation membrane of the invention and a method for separating a gas mixture. The gas separation membrane prepared from the functionalized polyimide can provide both better selectivity and better permeability for separating a gas mixture composition.

Description

Functionalized polyimides and membranes for gas separations Technical Field
The present invention relates to a functionalized polyimide, a high performance polyimide membrane for gas separations and a versatile process for chemical modification of aromatic polyimides.
Background art
Polymer membranes are applied in gas separations, as they allow separation of gases with low energy consumption and without use of absorbents. The performance of a polymer membrane in a gas separation process depends both on the gas permeability of the membrane and the permeation selectivity for the components of a gas mixture. However, there is a trade-off relation between permeability and selectivity, as membranes having high permeability usually have low selectivity and vice versa (L.M. Robeson, J. Membrane Sci. 320 (2008) 390-400) . It is very difficult to further improve membrane gas separation performance (to break Robeson’s upper-bound line) .
Polyimides are useful for making polymeric gas separation membranes, as they can provide both high mechanical stability, which allows their use at high gas pressures, as well as a combination of permeability and selectivity close to the Robeson upper boundary to membrane performance. The properties of polyimide gas separation membranes are usually tailored by choice of the dianhydride and diamine building blocks of the polyimide and by use of mixtures of dianhydride and diamine building blocks, i.e. by modifying the monomers used to make the polyimide.
M.D. Guiver and coworkers (Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 40, 4193-4204 (2002) ) reported a method for bromination of the commercial polyimide Matrimid and the resulting brominated Matrimid membrane exhibited approximately 60%higher gas permeability coefficients with slightly decreased selectivities.
Very recently Jong Suk Lee and coworkers (Journal of Membrane Science 545 (2018) 358-366) reported bromination of the polyimide derived from 4, 4’- (hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 2, 3, 5, 6-tetramethyl benzene-1, 4-diamine (Durene) and the resulting brominated polyimides with varied degrees of bromination (25-75%) exhibited much reduced gas permeability and moderately increased selectivity. Although they further reported that thermal treatment (360℃) of the brominated polyimides caused significantly (150-170%) enhanced gas permeability coefficients but the selectivity reduced to about one half of the values before the thermal treatment. Moreover, in comparison with other dianhydrides, 6FDA is an extremely expensive dianhydride monomer making it less useful in industrial applications.
K. Okamoto et al., Polym. J. 30 (1998) 492-498 describes functionalizing a polyimide prepared from 3, 3’, 4, 4’-biphenyltetracarboxylic dianhydride (BPDA) and 2, 4, 6-trimethyl-1, 3-phenylenediamine (TrMPD) by brominating benzylic methyl groups and reacting the resulting benzylic bromide groups with trimethyl phosphite or triethyl phosphite to provide a polyimide functionalized with phosphonate ester groups. The  functionalized polymer was crosslinked by heating or by reaction with 1, 2-diaminoethane. The functionalized and crosslinked polymer provided improved selectivity without reduction of permeation flux when used for separating a mixture of benzene and cyclohexane by pervaporation.
JPH 9-173801 describes a method for preparing gas separation membranes by brominating alkyl groups of an alkyl substituted polyimide, preparing a film from the resulting brominated polyimide and treating the brominated polyimide film with vapor or an aqueous solution of ammonia, a primary amine or a secondary amine. An alternative method is described in paragraph [0023] , where the brominated polyimide is reacted with a secondary amine, such as diethanol amine or morpholine, in solution to provide an amine-modified polyimide, followed by preparing the membrane by coating or casting a solution of the amine-modified polyimide on a substrate. The amine-modified polyimide membranes show an increase in selectivity compared to the non-modified polyimide membranes in gas separation, but permeability is considerably decreased.
Summary of the invention
The objective of this invention is to develop a versatile approach by which polyimide membranes with both significantly enhanced gas permeability coefficients and good selectivities at the same time can be produced.
The inventors of the present invention have now found that imide functionalized polyimides can be prepared by brominating an aromatic polyimide comprising benzylic groups and reacting the resulting brominated polyimide with a cyclic imide salt, preferably an alkali metal salt of a cyclic imide. The inventors have also found that gas separation membranes prepared from such an imide functionalized polyimide can provide both better selectivity and good permeability for separating a gas mixture, compared with the pristine polyimide.
A subject of the invention is therefore a method for preparing a functionalized polyimide, comprising the steps of
a) providing a solution of a polyimide with repeat units (I)
Figure PCTCN2018077544-appb-000001
where each R A, independently of one another, is an aromatic dianhydride monomer unit, each R B, independently of one another, is an aromatic diamine monomer unit, and at least part of said aromatic diamine monomer units R B comprise one or more methyl groups on the aromatic ring;
b) reacting the solution of step a) with a brominating agent and an initiator or photoinitiation to convert at least part of said methyl groups to bromomethylene groups, providing a brominated polyimide, preferably the degree of bromination is 20%-150%, for example 20%-140%, 20%-140%,  20%-130%, more preferably 20%-120%, even more preferably 30%-75%;
c) providing a solution of said brominated polyimide of step b) in a solvent; and
d) reacting the solution of step c) with a cyclic imide salt to convert at least part of the bromomethylene groups to imidomethylene groups.
The imidomethylene groups are formed by reacting the imido anion groups of the cyclic imide salt with the bromomethylene groups of the brominated polyimide.
In some embodiments, at least 5 mol-%, preferably at least 10 mol-%, for example, from 5 to 100 mol-%, 10 to 100 mol-%, 10 to 99 mol-%, 10 to 95 mol-%, 10 to 90 mol-%, 10 to 85 mol-%, 10 to 80 mol-%, 20 to 100 mol-%, 20 to 99 mol-%, 20 to 95 mol-%, 20 to 90 mol-%, 20 to 85 mol-%, 20 to 80 mol-%, 30 to 100 mol-%, 30 to 99 mol-%, 30 to 95 mol-%, 30 to 90 mol-%, 30 to 85 mol-%, 30 to 80 mol-%of bromomethylene groups are converted to imidomethylene groups in step d) .
The polyimide of step a) may be used to prepare gas separation membranes. However, compared with the functionalized polyimide obtained in step d) , the gas separation membranes prepared from the polyimide of step a) have lower gas separation efficiency.
The degree of bromination may be determined according to conventional methods such as elemental analysis and/or  1H NMR spectra, typically elemental analysis.
The mol-%of bromomethylene groups converted to imidomethylene groups may be determined according to the method of elemental analysis.
As used herein, a cyclic imide is an imide comprising two acyl groups bound to a nitrogen atom, in which the two carbonyl carbons are connected by a substituted or non-substituted carbon chain or substituted or non-substituted aromatic group. As used herein, a cyclic imide salt is a tertiary amine salt formed by said cyclic imide.
The cyclic imide salt is preferably a cyclic imide alkaline metal salt, more preferably a cyclic imide potassium or sodium salt. The cyclic imide salt may have the following general structure (II) :
Figure PCTCN2018077544-appb-000002
wherein Ar represents:
Figure PCTCN2018077544-appb-000003
each R 1 to R 6 independently of each other being hydrogen, or a C 1 to C 4 alkyl group unsubstituted or substituted by one or more halogen groups such as fluoro-, chloro-and bromo-group; the C 1 to C 4 alkyl group is preferably selected from –CH 3, -CF 3, -CH (CH 3)  2, and –C (CH 3)  3; and
M + represents a metal ion, preferably an alkaline metal ion, especially K + or Na +.
When the cyclic imide salt comprises a naphthalene ring, it is preferably unsubstituted on the naphthalene ring. When the cyclic imide salt comprises a benzene ring, it preferably comprises no or only one alkyl substituent group on the benzene ring.
Examples of the cyclic imide salt may be selected from an alkali metal α-methyl-α-phenylsuccinimide salt, an alkali metal succinimide salt, an alkali metal phthalimide salt or an alkali metal salt of naphthalene 1, 8-dicarboxylic acid imide.
Further subjects of the invention are the functionalized polyimide including the functionalized polyimide obtainable by this method, a gas separation membrane comprising the functionalized polyimide of the invention, a gas separation device comprising the gas separation membrane of the invention and a method for separating a gas mixture comprising contacting the mixture with the gas separation membrane of the invention and applying a pressure difference across the gas separation membrane to effect permeation of at least one component of the gas mixture through the gas separation membrane.
Preferably, the polyimide may be a polymer of structure (III)
Figure PCTCN2018077544-appb-000004
where the aromatic dianhydride monomer units R A, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000005
Figure PCTCN2018077544-appb-000006
the aromatic diamine monomer units R B1, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000007
Figure PCTCN2018077544-appb-000008
with each R 1 to R 7 independently of each other being hydrogen or a methyl group with the proviso that at least one of R 1 to R 3 is different from hydrogen, and at least one of R 4 to R 7 is different from hydrogen;
R 8 being hydrogen or a C 1 to C 3 alkyl group unsubstituted or substituted by one or more halogen groups such as fluoro-, chloro-and bromo-group, preferably hydrogen or methyl;
and the aromatic diamine monomer units R B2, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000009
and x is from 0.1 to 1, for example 0.15 to 1, 0.2 to 1, 0.25 to 1, 0.3 to 1, 0.35 to 1, 0.4 to 1, 0.45 to 1, 0.5 to 1, 0.55 to 1, 0.6 to 1, 0.65 to 1, 0.7 to 1, 0.75 to 1, 0.8 to 1, 0.85 to 1, 0.9 to 1, 0.95 to 1.
In some embodiments, the aromatic diamine monomer units R B1, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000010
Figure PCTCN2018077544-appb-000011
In some embodiments, the aromatic diamine monomer units R B1, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000012
In some embodiments, the aromatic dianhydride monomer units R A, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000013
In some embodiments, the polyimide is a polymer, especially a block copolymer of structure (IV)
Figure PCTCN2018077544-appb-000014
where the aromatic dianhydride monomer units R A1, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000015
the aromatic diamine monomer units R B3, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000016
the aromatic dianhydride monomer units R A2, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000017
and the aromatic diamine monomer units R B4, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000018
with each R 1 to R 7 independently of each other being hydrogen or a methyl group; R 8 being as stated above;
y is from 5 to 500,
z is from 5 to 500, and
R A1 is different from R A2, R B3 is different from R B4 or both R A1 is different from R A2 and R B3 is different from R B4.
In some embodiments, R B4 of the polyimide above is selected from the group consisting of:
Figure PCTCN2018077544-appb-000019
As used herein, the term “functionalized polyimide” refers to the polyimide after functionalizing the brominated polyimide with the cyclic imide salt, unless otherwise explicitly specified.
The invention provides a technical approach for producing functionalized polyimides with significantly improved gas separation performance. It involves bromination of the polyimides derived from methyl-substituted diamines in the first step and functionalization with a cyclic imide salt in the next step. The bromination reaction can be performed by heating a solution mixture containing a polyimide, a brominating reagent and an initiator or photoinitiation. The methylene bromide groups of the resulting brominated polyimide undergo a next step functionalization with the cyclic imide salt to give the desired product. The pristine polyimides are polyimides with repeat units (I) , preferably polymer of structure (III) .
In some embodiments, the method to prepare a functionalized polyimide comprises the following steps:
A) dissolving a polyimide with repeat units (I) , preferably polymer of structure (III) in an organic solvent, adding a brominating reagent and an initiator, reacting at 60-120℃ for 0.5-24 hrs, preferably 70-100 ℃ for 2-10 hrs and obtaining a brominated polyimide; wherein the molar ratio between methyl groups of the polyimide and the brominating reagent is controlled at 20-1: 1; and
B) dissolving the brominated polyimide in an organic solvent, typically under nitrogen atmosphere, adding a cyclic imide salt, and reacting at 30-120 ℃ for 1-60 hrs, for example 2-60 hrs, 2-48 hrs, 2-36 hrs, 2-24hrs or 1-24 hrs and obtaining the functionalized polyimide.
In some embodiments, the reaction of step b) is conducted at 60-120℃ for 0.5-24 hrs, preferably 70-100 ℃ for 2-10 hrs.
In some embodiments, the reaction of step d) is conducted at 30-120 ℃ for 1-60 hrs, for example 2-60 hrs, 2-48 hrs, 2-36 hrs, 2-24hrs or 1-24 hrs.
In some embodiments, the molar ratio between the brominated polyimide and the cyclic imide salt is 1: 0.05 to 1: 5, preferably 1: 0.1 to 1: 2.
In some embodiments, the reaction product obtained in step (a) is cooled to room temperature, then the solution mixture is poured in to a nonsoluble organic liquid (non-solvent) such as methanol, the resulting precipitate is collected by filtration, thoroughly washed with the nonsoluble organic liquid and dried in vacuum to yield the brominated polyimide.
In some embodiments, the reaction product obtained in step (b) is cooled to room temperature, then the solution mixture is poured into a nonsoluble organic liquid such as methanol and the resulting precipitate is collected by filtration, thoroughly washed with deionized water, and dried in a vacuum oven to yield the functionalized polyimide.
The methyl groups of the above mentioned polyimides can be readily brominated by reacting with a conventional brominating reagent such as N-bromosuccinimide (NBS) , dibromoisocyanuric acid and 1, 3-dibromo-5, 5-dimethyl hydantoin in the presence of an initiator such as benzoyl peroxide (BPO) . By controlling the reaction conditions, for example in a temperature between 60-120℃, reaction time between 0.5-24 hr, the molar ratio between methyl groups and brominating reagent such as NBS being 20-1: 1, the degree of bromination can be controlled.
Conventional organic solvents such as 1, 1, 2, 2-tetrachloroethane (TCE) , chloroform, methylene dichloride, N, N-dimethylforamide (DMF) , N, N-dimethylacetamide (DMAc) and 1-methylpyrrolidinone (NMP) can be used for dissolving the polyimides depending on their individual chemical structures. After the completion of the bromination reaction, the reaction mixture may be poured into a nonsoluble organic liquid such as methanol and acetone. The precipitate (brominated polyimide) may be collected by filtration and dried in a vacuum oven.
Preferably, 0.3-1 equivalent (eq. ) of N-bromosuccinimide (NBS) is used for the bromination reaction to give the degree of bromination of 30%-74%. Preferably, 1, 1, 2, 2-tetrachloroethane (TCE) and/or N, N-dimethylforamide (DMF) are used as the solvents for bromination reaction. Preferably, the bromination reaction is carried out at 70-100 ℃ for 2-10 hrs.
The above brominated polyimide can be dissolved in a conventional solvent such as dichloromethane, chloroform, 1, 1, 2, 2-tetrachloroethane (TCE) , N, N-dimethylforamide (DMF) , N, N-dimethylacetamide (DMAc) and 1-methylpyrrolidinone (NMP) , etc. to give a 1-30 w/v%solution. Then a cyclic imide salt (such as potassium phthalimide, ) is added and the mixture is heated at 30-120 ℃ for 1-60 hrs, for example 2-60 hrs, 2-48 hrs, 2-36 hrs, 1-24 hrs or 2-24 hrs. After cooling to room temperature, the solution mixture can be poured into a nonsoluble organic liquid such as methanol and the resulting precipitate can be collected by filtration, thoroughly washed with deionized water, and dried in a vacuum oven.
In some embodiments, phthalimide potassium salt and naphthalimide potassium salt are selected to react with the brominated polyimides, for example at 40 ℃ for 24 hrs.
In some embodiments, the brominating agent is selected from N-bromosuccinimide, dibromoisocyanuric acid and 1, 3-dibromo-5, 5-dimethyl hydantoin.
In some embodiments, the photoinitiation is by irradiation with UV light.
In some embodiments, the initiator is used by addition of an organic peroxide and heating.
In some embodiments, the organic peroxide is a dialkylperoxide, an alkyl acyl peroxide or a diacylperoxide, preferably a diacylperoxide, more preferably dibenzoylperoxide.
In some embodiments, the molar ratio of brominating agent to the benzylic groups of said aromatic diamine monomer units R B is from 0.05 to 1.
In some embodiments, step b) is carried out in a chlorohydrocarbon solution, preferably in a 1, 1, 2, 2-tetrachloroethane solution.
In some embodiments, step b) is carried out in a carboxylic acid dialkylamide solution, preferably a solution in N, N-dimethylformamide, N, N-dimethylacetamide or N-methylpyrolidone.
In some embodiments, the cyclic imide salt is an alkali metal cyclic imide salt.
In some embodiments, the alkali metal cyclic imide salt is selected from an alkali metal α-methyl-α-phenylsuccinimide salt, an alkali metal succinimide salt, an alkali metal phthalimide salt or an alkali metal salt of naphthalene 1, 8-dicarboxylic acid imide.
In some embodiments, step d) is carried out in a carboxylic acid dialkylamide solution, preferably a solution in N, N-dimethylformamide, N, N-dimethylacetamide or N-methylpyrolidone.
In some embodiments, wherein step d) is carried out at a temperature of from 30 to 120 ℃.
In some embodiments, in step b) the brominating agent is N-bromosuccinimide or dibromoisocyanuric acid and steps c) and d) are carried out by adding an alkali metal alkoxide to the solution obtained in step b) in an amount sufficient for converting the succinimide or phthalimide formed in step b) into the alkali metal succinimide salt or alkali metal phthalimide salt.
A further subject of the invention is a functionalized polyimide, obtainable by a method according to the present invention.
A further subject of the invention is a functionalized polyimide, wherein the polyimide is a polymer, including a random copolymer of structure (III)
Figure PCTCN2018077544-appb-000020
wherein the aromatic dianhydride monomer units R A, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000021
the aromatic diamine monomer units R B1, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000022
Figure PCTCN2018077544-appb-000023
with each R 1 to R 7 independently of each other being hydrogen or a group R c with the proviso that at least one of R 1 to R 3 is different from hydrogen, and at least one of R 4 to R 7 is different from hydrogen,
R 8 being hydrogen or a C 1 to C 3 alkyl group unsubstituted or substituted by one or more halogen groups such as fluoro-, chloro-and bromo-group, preferably hydrogen or methyl,
R c being methyl or a CH 2R d group with the proviso that at least 5 mol-%, for example at least 10 mol-%, at least 15 mol-%, at least 20 mol-%, at least 25 mol-%, at least 30 mol-%, at least 35 mol-%, at least 40 mol-%, at least 45 mol-%, at least 50 mol-%, at least 55 mol-%, at least 60 mol-%, at least 65 mol-%, at least 70 mol-%, at least 75 mol-%, at least 80 mol-%, at least 85 mol-%, at least 90 mol-%of groups R c are CH 2R d groups, for example from 5 to 100 mol-%, 10 to 100 mol-%, 10 to 99 mol-%, 10 to 95 mol-%, 10 to 90 mol-%, 10 to 85 mol-%, 10 to 80 mol-%, 10 to 75 mol-%, 10 to 70 mol-%, 10 to 65 mol-%, 10 to 60 mol-%, 10 to 55 mol-%, 10 to 50 mol-%, 10 to 45 mol-%, 10 to 40 mol-%, 20 to 100 mol-%, 20 to 99 mol-%, 20 to 95 mol-%, 20 to 90 mol-%, 20 to 85 mol-%, 20 to 80 mol-%, 20 to 75 mol-%, 20 to 70 mol-%, 20 to 65 mol-%, 20 to 60 mol-%, 20 to 55 mol-%, 20 to 50 mol-%, 20 to 45 mol-%, 20 to 40 mol-%, 30 to 100 mol-%, 30 to 99 mol-%, 30 to 95 mol-%, 30 to 90 mol-%, 30 to 85 mol-%, 30 to 80 mol-%, 30 to 75 mol-%, 30 to 70 mol-%, 30 to 65 mol-%, 30 to 60 mol-%, 30 to 55 mol-%, 30 to 50 mol-%, 30 to 45 mol-%, 30 to 40 mol-%of groups R c are CH 2R d groups,
R d being structure (II’) :
Figure PCTCN2018077544-appb-000024
wherein Ar represents:
Figure PCTCN2018077544-appb-000025
each R 1 to R 6 independently of each other being hydrogen, or a C 1 to C 4 alkyl group unsubstituted or substituted by one or more halogen groups such as fluoro-, chloro-and bromo-group; the C 1 to C 4 alkyl group is preferably selected from –CH 3, -CF 3, -CH (CH 3)  2, and –C (CH 3)  3;
and the aromatic diamine monomer units R B2, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000026
and x is from 0.1 to 1, for example 0.15 to 1, 0.2 to 1, 0.25 to 1, 0.3 to 1, 0.35 to 1, 0.4 to 1, 0.45 to 1, 0.5 to 1, 0.55 to 1, 0.6 to 1, 0.65 to 1, 0.7 to 1, 0.75 to 1, 0.8 to 1, 0.85 to 1, 0.9 to 1, 0.95 to 1.
It should be understood that the unfunctionalized polyimide is the polyimide of structure (III) but has R c being all methyl. In other words, the unfunctionalized polyimide is functionalized by R d group on at least part of the methyl groups. Such unfunctionalized polyimide may also be used to prepare gas separation membranes. However, compared with the functionalized polyimide of structure (III) , the gas separation membranes prepared from such unfunctionalized polyimide have lower gas separation efficiency.
In some embodiments, each R 1 to R 7 in the aromatic diamine monomer unit R B1 of the functionalized polyimide above is a group R c.
In some embodiments, in the functionalized polyimide above, x is 1 and the aromatic diamine monomer units R B1, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000027
In some embodiments, in the functionalized polyimide above, the aromatic dianhydride monomer units R A, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000028
In some embodiments, in the functionalized polyimide above, the polyimide is a polymer, including a block copolymer of structure (IV)
Figure PCTCN2018077544-appb-000029
where the aromatic dianhydride monomer units R A1, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000030
the aromatic diamine monomer units R B3, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000031
with R c being methyl or a CH 2R d group with the proviso that at least 5 mol-%, for example at least 10 mol-%, at least 15 mol-%, at least 20 mol-%, at least 25 mol-%, at least 30 mol-%, at least 35 mol-%, at least 40 mol-%, at least 45 mol-%, at least 50 mol-%, at least 55 mol-%, at least 60 mol-%, at least 65 mol-%, at least 70 mol-%, at least 75 mol-%, at least 80 mol-%, at least 85 mol-%, at least 90 mol-%of groups R c are CH 2R d groups, for example from 5 to 100 mol-%, 10 to 100 mol-%, 10 to 99  mol-%, 10 to 95 mol-%, 10 to 90 mol-%, 10 to 85 mol-%, 10 to 80 mol-%, 10 to 75 mol-%, 10 to 70 mol-%, 10 to 65 mol-%, 10 to 60 mol-%, 10 to 55 mol-%, 10 to 50 mol-%, 10 to 45 mol-%, 10 to 40 mol-%, 20 to 100 mol-%, 20 to 99 mol-%, 20 to 95 mol-%, 20 to 90 mol-%, 20 to 85 mol-%, 20 to 80 mol-%, 20 to 75 mol-%, 20 to 70 mol-%, 20 to 65 mol-%, 20 to 60 mol-%, 20 to 55 mol-%, 20 to 50 mol-%, 20 to 45 mol-%, 20 to 40 mol-%, 30 to 100 mol-%, 30 to 99 mol-%, 30 to 95 mol-%, 30 to 90 mol-%, 30 to 85 mol-%, 30 to 80 mol-%, 30 to 75 mol-%, 30 to 70 mol-%, 30 to 65 mol-%, 30 to 60 mol-%, 30 to 55 mol-%, 30 to 50 mol-%, 30 to 45 mol-%, 30 to 40 mol-%of groups R c are CH 2R d groups,
R d being structure (II’) :
Figure PCTCN2018077544-appb-000032
wherein Ar represents:
Figure PCTCN2018077544-appb-000033
each R 1 to R 6 independently of each other being hydrogen, or a C 1 to C 4 alkyl group unsubstituted or substituted by one or more halogen groups such as fluoro group; the C 1 to C 4 alkyl group is preferably selected from –CH 3, -CF 3, -CH (CH 3)  2, and –C (CH 3)  3;
the aromatic dianhydride monomer units R A2, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000034
and the aromatic diamine monomer units R B4, independently of one another, are selected from the group consisting of:
Figure PCTCN2018077544-appb-000035
with each R 1 to R 7 independently of each other being hydrogen or a group R c as defined above; R 8 being as defined above;
y is from 5 to 500,
z is from 5 to 500, and
R A1 is different from R A2, R B3 is different from R B4 or both R A1 is different from R A2 and R B3 is different from R B4.
In some embodiments, R B4 is selected from the group consisting of:
Figure PCTCN2018077544-appb-000036
The polyimide polymer of the invention may be either homopolymer or copolymer. The type of copolymer is not limited, for example, the copolymer may be alternating copolymer, periodic copolymer, statistical copolymer, block copolymer etc.
The functionalized polyimide of the invention is suitable to prepare a gas separation membrane.
A further subject of the invention is a gas separation membrane, comprising a functionalized polyimide of the present invention.
In some embodiments, the membrane is prepared from the functionalized polyimide of the present invention.
In some embodiments, the membrane is asymmetrical with a non-porous polyimide film on a porous layer.
In some embodiments, the membrane has the shape of a hollow fibre.
A further subject of the invention is method for separating a gas mixture, comprising contacting the mixture with a gas separation membrane according to the present invention and applying a pressure difference across the gas separation membrane to effect permeation of at least one component of the gas mixture through the gas separation membrane.
A further subject of the invention is a gas separation device, comprising the gas separation membrane of the present invention.
The functionalized polyimide membranes of this invention exhibited both significantly enhanced gas permeability coefficients and good selectivities at the same time.
Membranes can be fabricated by conventional methods. For example, membranes can be fabricated by solution cast method with a 2-25 w/v%polymer solution.
Gas permeability coefficient is closely dependent on polymer fractional free volume (V F) and the higher V F, the higher permeability coefficient. As disclosed in the invention, the introduction of cyclic imide groups into polyimide structure is an effective approach to increase membrane free volume, and therefore higher permeability is achieved. On the other hand, selectivity is closely related to the interaction between polymer segments and penetrant gas molecules. A polymeric membrane with high affinity for one kind of penetrant but little affinity for another penetrant tends to has high selectivity. Through proper functionalization as disclosed in this invention, the modified polyimides exhibited greatly enhanced affinity for gases such as CO 2 and O 2 but little affinity for gases such as N 2 and CH 4 leading to higher or similar selectivity. The membranes made by the functionalized polyimide of the invention is especially suitable for separation of gases for example CO 2/N 2, CO 2/CH 4, O 2/N 2.
The invention grafts highly polar and bulky functional groups into polyimide backbone via proper chemical modifications (bromination and functionalization) and results in greatly enhanced gas permeability coefficients and enhanced selectivities at the same time.
The method of the invention is applicable to a broad range of polyimides of which structure contains methyl groups in the diamine moieties (polyimides derived from methyl-substituted diamines) . The reaction conditions are moderate and easy to control.
Other advantages of the present invention would be apparent for a person skilled in the art upon reading the specification.
Brief Description of Drawings
Figure 1 shows the Fourier transform infrared (FT-IR) spectroscopy analysis result of the functionalized polyimide obtained in Example 4.
Detailed description of the invention
The invention is now described in detail by the following examples. The scope of the invention should not be limited to the embodiments of the examples.
Analytical Procedures
The tensile strength was determined with a universal tensile machine (Instron 4465, commercially available from Instron Co. Ltd., U.S.A. ) . The samples were 80 mm long, 5 mm wide and 30-50 μm thick. The cross-head rate was 2 mm/min.
The gas permeability was determined with a gas solubility and diffusivity test machine GTR-1ADFE (commercially available from GTR Tec Corporation, Japan) . The test was performed at an upstream pressure of 0.1-0.4 MPa at 35 ℃. The measurement was based on a vacuum time-lag method and the gas permeability coefficient (P) was determined from a steady state permeation flux in a period between 5 and 10 times the time lag (θ) . The effective membrane area was 15.2 cm 2.
The degree of bromination was determined by elemental analysis using an elemental analyzer (Vario EL Cube, Germany) .
The mol-%of bromomethylene groups converted to imidomethylene groups was also determined according to the method of elemental analysis.
The FT-IR was recorded on a Paragon 1000PC FT-IR spectrometer (Perkin Elmer, Inc., USA) using a polyimide film.
Example 1: preparation of polyimide BPDA-TrMPD
To a 100 mL completely dried three-neck flask 3.00 g of 2, 4, 6-trimethyl-1, 3-phenylenediamine (TrMPD) and 60 mL of 1-methylpyrrolidinone (NMP) were added with nitrogen purge, and the mixture was continuously stirred at room temperature. Then, 5.88 g of 3, 3’, 4, 4’-biphenyltetracarboxylic dianhydride (BPDA) was added portion-wise within 3 hrs. After complete addition of BPDA, the reaction mixture was further stirred for additional 5 hrs. The solution mixture was slowly heated to 80 ℃ followed by addition of 20 mL of xylene through a dropping funnel. With slow addition of xylene the reaction mixture was further heated to 180 ℃ and kept at this temperature for 10 hrs. After cooling to room temperature, the highly viscous solution was poured into methanol and fiber-like precipitate was collected by filtration and finally dried in a vacuum oven at 120 ℃ for 10 hrs. The polyimide product was denoted as BPDA-TrMPD.
Example 2: bromination of polyimide BPDA-TrMPD
1.0 g (2.45 mmol) of BPDA-TrMPD and 20 ml of 1, 1, 2, 2-tetrachloroethane (TCE) were placed in a 150 ml dry three-neck flask equipped with a condenser. Next, 0.302 g (1.72 mmol) of N-bromosuccinimide (NBS) and 0.0207 g of benzoyl peroxide (BPO) were added. The mixture was stirred at 85 ℃ for 6 hrs. After cooling to room temperature, the solution mixture was poured in to methanol. The precipitate was collected by filtration, thoroughly washed with MeOH and finally dried at 80 for 10 hrs in vacuum. The  produced brominated polyimide was denoted as PI-0.7Br, here “0.7” refers to the molar ratio of NBS to BPDA-TrMPD in feed. From the elemental analysis data, the degree of bromination of this polyimide was calculated to be 59%. It exhibited a tensile strength of 72 MPa and an elongation at break of 87%.
Elemental analysis result of the brominated polyimide obtained in Example 2 was as follows,
C: 65.55%, H: 4.17%, N: 5.94%, O: 13.98%, Br: 10.36%.
1H NMR spectrum of the brominated BPDA-TrMPD polyimide obtained in Example 2 in DMSO-d6 showed that the methyl groups on the aromatic ring were partly converted bromomethylene groups and the desired brominated polyimide was obtained.
Example 3: bromination of polyimide BPDA-TrMPD
The above procedures were followed except that the molar ratio of NBS to BPDA-TrMPD in feed was controlled at 0.3: 1 yielding the brominated polyimide with the degree of bromination of 30%. It exhibited a tensile strength of 73 MPa and an elongation at break of 27%.
Changing the molar ratio of NBS to BPDA-TrMPD in feed to 0.5: 1 and 1: 1 resulted in the brominated polyimides PI-0.5Br and PI-1.0 Br with the degrees of bromination of 46%and 74%, respectively. The tensile strength and elongation at break values are 74 MPa and 44%for PI-0.5Br and 73 MPa and 80%for PI-1.0Br.
Example 4: reaction of brominated polyimide with a cyclic imide salt
To a 150 mL dry three-neck flask armed with a condenser 0.5 g of PI-0.7Br and 30 ml of TCE were added. The mixture was continuously stirred to allow complete dissolution of the solid. Then, 0.2 g of phthalimide potassium salt was added. The reaction temperature was maintained at 40 ℃ for 24 hrs. The solution mixture was directly cast onto a clean glass plate and placed in an air oven at 60 ℃ for 8 h. The film was peeled off and thoroughly washed with methanol and water successively, and finally dried in a vacuum oven at 120 ℃ for 10 hrs. It exhibited a tensile strength of 68 MPa and an elongation at break of 16%.
Characterization of functionalized polyimide
The Fourier transform infrared (FT-IR) spectroscopy analysis result of a membrane prepared by the functionalized polyimide obtained in Example 4 was as shown in Figure 1.
Elemental analysis was performed using the functionalized polyimide obtained in Example 4. Two tests were done for the polyimide.
The elemental analysis result of the functionalized polyimide obtained in Example 4 was as follows,
Table 1 Elemental analysis result
Test No. N [%] C [%] H [%] Other (Br + O)
1 5.80 66.63 4.69 22.88
2 5.86 66.19 4.13 23.82
Average 5.83 66.38 4.41 23.35
The conversion degree (mol-%of bromomethylene groups converted to imidomethylene groups) was calculated to be 44%based on carbon and 48%based on other atoms (Br + O) .
The FT-IR spectroscopy analysis and elemental analysis confirmed that the desired functionalized polyimide was obtained.
Example 5: gas permeability coefficient and selectivity tests
A 5 w/v%polymer solution in an organic solvent (TCE or NMP) was cast onto glass plates and dried in an air oven at 60℃ (for TCE) or 80 ℃ (for NMP) for 8 h. The as-cast membranes were peeled from the glass plates and further dried at 120 ℃ for 12 h in vacuo.
The gas permeability coefficients and ideal selectivities of the brominated polyimide membranes as well as the pristine polyimide membrane at 35 ℃ and 100 kPa (upstream pressure) are illustrated in Table 2.
Table 2 permeability coefficient and selectivity of membranes
Figure PCTCN2018077544-appb-000037
Note: the unit of permeability coefficient is Barrer (1 Barrer = 10 -10 cm 3*cm/cm 2*s*cmHg) .
Example 6: gas permeability coefficient and selectivity tests
The gas permeability coefficients and ideal selectivities of the phthalimide potassium salt-modified polyimide membrane (see Example 4) at 35 ℃ and 100 kPa (upstream pressure) were determined and illustrated in Table 3. For comparison purpose, the relevant data of the PI-0.7Br and the pristine polyimide (BPDA-TrMPD) membranes are also shown in this table. It is obvious that in comparison with the precursor membranes the phthalimide-potassium-salt-modified polyimide membrane exhibited both significantly enhanced gas permeability coefficients and enhanced selectivities.
Table 3 permeability coefficient and selectivity of membranes
Figure PCTCN2018077544-appb-000038
Note: the unit of permeability coefficient is Barrer (1 Barrer = 10 -10 cm 3*cm/cm 2*s*cmHg) .
As used herein, terms such as "comprise (s) " and the like as used herein are open terms meaning 'including at least' unless otherwise specifically noted.
All references, tests, standards, documents, publications, etc. mentioned herein are incorporated herein by reference. Where a numerical limit or range is stated, the endpoints are included. Also, all values and subranges within a numerical limit or range are specifically included as if explicitly written out.
The above description is presented to enable a person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the preferred embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Thus, this invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. In this regard, certain embodiments within the invention may not show every benefit of the invention, considered broadly.

Claims (32)

  1. A method for preparing a functionalized polyimide, comprising the steps of
    a) providing a solution of a polyimide with repeat units (I)
    Figure PCTCN2018077544-appb-100001
    wherein each R A, independently of one another, is an aromatic dianhydride monomer unit, each R B, independently of one another, is an aromatic diamine monomer unit, and at least part of said aromatic diamine monomer units R B comprise one or more methyl groups on the aromatic ring;
    b) reacting the solution of step a) with a brominating agent and an initiator or photoinitiationto convert at least part of said methyl groups to bromomethylene groups, providing a brominated polyimide, preferably the degree of bromination is 20%-150%, for example 20%-120%, more preferably 30%-75%;
    c) providing a solution of said brominated polyimide of step b) in a solvent; and
    d) reacting the solution of step c) with a cyclic imide salt to convert at least part of the bromomethylene groups to imidomethylene groups; preferably at least 5 mol-%, more preferably at least 10 mol-%of bromomethylene groups are converted to imidomethylene groups in step d) .
  2. The method of claim 1, wherein the cyclic imide salt has the structure (II) :
    Figure PCTCN2018077544-appb-100002
    wherein Ar represents
    Figure PCTCN2018077544-appb-100003
    each R 1 to R 6 independently of each other being hydrogen, or a C 1 to C 4 alkyl group unsubstituted or substituted by one or more halogen groups such as fluoro-, chloro-and bromo-group; the C 1 to C 4 alkyl group is preferably selected from –CH 3, -CF 3, -CH (CH 3)  2, and –C (CH 3)  3; and
    M + represents a metal ion, preferably an alkaline metal ion, especially K + or Na +.
  3. The method of claim 1 or 2, wherein the polyimide is a polymer of structure (III)
    Figure PCTCN2018077544-appb-100004
    wherein the aromatic dianhydride monomer units R A, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100005
    the aromatic diamine monomer units R B1, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100006
    Figure PCTCN2018077544-appb-100007
    with each R 1 to R 7 independently of each other being hydrogen or a methyl group with the proviso that at least one of R 1 to R 3 is different from hydrogen, and at least one of R 4 to R 7 is different from hydrogen;
    R 8 being hydrogen or a C 1 to C 3 alkyl group unsubstituted or substituted by one or more halogen groups such as fluoro-, chloro-and bromo-group, preferably hydrogen or methyl;
    and the aromatic diamine monomer units R B2, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100008
    Figure PCTCN2018077544-appb-100009
    and x is from 0.1 to 1, for example 0.15 to 1, 0.2 to 1, 0.25 to 1, 0.3 to 1, 0.35 to 1, 0.4 to 1, 0.45 to 1, 0.5 to 1, 0.55 to 1, 0.6 to 1, 0.65 to 1, 0.7 to 1, 0.75 to 1, 0.8 to 1, 0.85 to 1, 0.9 to 1, 0.95 to 1.
  4. The method of claim 3, wherein the aromatic diamine monomer units R B1, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100010
  5. The method of claim 3, wherein the aromatic diamine monomer units R B1, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100011
    and x is 1.
  6. The method of claim 5, wherein the aromatic dianhydride monomer units R A, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100012
  7. The method of claim 1 or 2, wherein the polyimide is a polymer, especially a block copolymer of structure (IV)
    Figure PCTCN2018077544-appb-100013
    where the aromatic dianhydride monomer units R A1, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100014
    the aromatic diamine monomer units R B3, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100015
    the aromatic dianhydride monomer units R A2, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100016
    and the aromatic diamine monomer units R B4, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100017
    with each R 1 to R 7 being as defined above; R 8 being as stated above;
    y is from 5 to 500,
    z is from 5 to 500, and
    R A1 is different from R A2, R B3 is different from R B4 or both R A1 is different from R A2 and R B3 is different from R B4.
  8. The method of claim 7, wherein R B4 is selected from the group consisting of:
    Figure PCTCN2018077544-appb-100018
  9. The method of any one of the preceding claims, wherein the brominating agent is selected from N-bromosuccinimide, dibromoisocyanuric acid and 1, 3-dibromo-5, 5-dimethyl hydantoin.
  10. The method of any one of the preceding claims, wherein the photoinitiation is by irradiation with UV light.
  11. The method of any one of claims 1 to 10, wherein the initiator is used by addition of an organic peroxide and heating.
  12. The method of claim 11, wherein the organic peroxide is a dialkylperoxide, an alkyl acyl peroxide or a diacylperoxide, preferably a diacylperoxide, more preferably dibenzoylperoxide.
  13. The method of any one of the preceding claims, wherein the molar ratio of brominating agent to the benzylic groups of said aromatic diamine monomer units R B is from 0.05 to 1.
  14. The method of any one of the preceding claims, wherein step b) is carried out in a chlorohydrocarbon solution, preferably in a 1, 1, 2, 2-tetrachloroethane solution.
  15. The method of any one of claims 1 to 14, wherein step b) is carried out in a carboxylic acid dialkylamide solution, preferably a solution in N, N-dimethylformamide, N, N-dimethylacetamide or N-methylpyrolidone.
  16. The method of any one of the preceding claims, wherein the cyclic imide salt is an alkali metal cyclic imide salt.
  17. The method of claim 16, wherein the alkali metal cyclic imide salt is selected from an alkali metal α-methyl-α-phenylsuccinimide salt, an alkali metal succinimide salt, an alkali metal phthalimide salt or an alkali metal salt of naphthalene 1, 8-dicarboxylic acid imide.
  18. The method of any one of the preceding claims, wherein step d) is carried out in a carboxylic acid dialkylamide solution, preferably a solution in N, N-dimethylformamide, N, N-dimethylacetamide or N-methylpyrolidone.
  19. The method of any one of the preceding claims, wherein step d) is carried out at a temperature of from 30 to 120 ℃.
  20. The method of any one of the preceding claims, wherein in step b) the brominating agent is N-bromosuccinimide or dibromoisocyanuric acid and steps c) and d) are carried out by adding an alkali metal alkoxide to the solution obtained in step b) in an amount sufficient for converting the succinimide or phthalimide formed in step b) into the alkali metal succinimide salt or alkali metal phthalimide salt.
  21. A functionalized polyimide, obtainable by a method according to any one of claims 1 to 20.
  22. A functionalized polyimide, wherein the polyimide is a polymer, including a random copolymer of structure (III)
    Figure PCTCN2018077544-appb-100019
    wherein the aromatic dianhydride monomer units R A, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100020
    Figure PCTCN2018077544-appb-100021
    the aromatic diamine monomer units R B1, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100022
    Figure PCTCN2018077544-appb-100023
    with each R 1 to R 7 independently of each other being hydrogen or a group R c with the proviso that at least one of R 1 to R 3 is different from hydrogen, and at least one of R 4 to R 7 is different from hydrogen, R 8 being hydrogen or a C 1 to C 3 alkyl group unsubstituted or substituted by one or more halogen groups such as fluoro-, chloro-and bromo-group, preferably hydrogen or methyl,
    R c being methyl or a CH 2R d group with the proviso that at least 5 mol-%, for example at least 10 mol-%, at least 15 mol-%, at least 20 mol-%, at least 25 mol-%, at least 30 mol-%, at least 35 mol-%, at least 40 mol-%, at least 45 mol-%, at least 50 mol-%, at least 55 mol-%, at least 60 mol-%, at least 65 mol-%, at least 70 mol-%, at least 75 mol-%, at least 80 mol-%, at least 85 mol-%, at least 90 mol-%of groups R c are CH 2R d groups, for example 5 to 100 mol-%-%, 10 to 100 mol-%, 10 to 99 mol-%, 10 to 95 mol-%, 10 to 90 mol-%, 10 to 85 mol-%, 10 to 80 mol-%, 10 to 75 mol-%, 10 to 70 mol-%, 10 to 65 mol-%, 10 to 60 mol-%, 10 to 55 mol-%, 10 to 50 mol-%, 10 to 45 mol-%, 10 to 40 mol-%, 20 to 100 mol-%, 20 to 99 mol-%, 20 to 95 mol-%, 20 to 90 mol-%, 20 to 85 mol-%, 20 to 80 mol-%, 20 to 75 mol-%, 20 to 70 mol-%, 20 to 65 mol-%, 20 to 60 mol-%, 20 to 55 mol-%, 20 to 50 mol-%, 20 to 45 mol-%, 20 to 40 mol-%, 30 to 100 mol-%, 30 to 99 mol-%, 30 to 95 mol-%, 30 to 90 mol-%, 30 to 85 mol-%, 30 to 80 mol-%, 30 to 75 mol-%, 30 to 70 mol-%, 30 to 65 mol-%, 30 to 60 mol-%, 30 to 55 mol-%, 30 to 50 mol-%, 30 to 45 mol-%, 30 to 40 mol-%of groups R c are CH 2R d groups,
    R d being structure (II’) :
    Figure PCTCN2018077544-appb-100024
    wherein Ar represents:
    Figure PCTCN2018077544-appb-100025
    each R 1 to R 6 independently of each other being hydrogen, or a C 1 to C 4 alkyl group unsubstituted or substituted by one or more halogen groups such as fluoro-, chloro-and bromo-group; the C 1 to C 4 alkyl group is preferably selected from –CH 3, -CF 3, -CH (CH 3)  2, and –C (CH 3)  3;
    and the aromatic diamine monomer units R B2, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100026
    and x is from 0.1 to 1, for example 0.15 to 1, 0.2 to 1, 0.25 to 1, 0.3 to 1, 0.35 to 1, 0.4 to 1, 0.45 to 1, 0.5 to 1, 0.55 to 1, 0.6 to 1, 0.65 to 1, 0.7 to 1, 0.75 to 1, 0.8 to 1, 0.85 to 1, 0.9 to 1, 0.95 to 1.
  23. The functionalized polyimide of claim 22, wherein each R 1 to R 7 is a group R c.
  24. The functionalized polyimide of claim 22, wherein x is 1 and the aromatic diamine monomer units R B1, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100027
  25. The functionalized polyimide of claim 24, wherein the aromatic dianhydride monomer units R A, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100028
  26. The functionalized polyimide of claim 22, wherein the polyimide is a polymer, including a block copolymer of structure (IV)
    Figure PCTCN2018077544-appb-100029
    where the aromatic dianhydride monomer units R A1, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100030
    the aromatic diamine monomer units R B3, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100031
    with R c being as defined above;
    R d being as defined above;
    the aromatic dianhydride monomer units R A2, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100032
    and the aromatic diamine monomer units R B4, independently of one another, are selected from the group consisting of:
    Figure PCTCN2018077544-appb-100033
    with each R 1 to R 8 being as defined above;
    y is from 5 to 500,
    z is from 5 to 500, and
    R A1 is different from R A2, R B3 is different from R B4 or both R A1 is different from R A2 and R B3 is different from R B4.
  27. The functionalized polyimide of claim 26, wherein R B4 is selected from the group consisting of:
    Figure PCTCN2018077544-appb-100034
  28. A gas separation membrane, comprising a functionalized polyimide of any one of claims 21 to 27.
  29. The gas separation membrane of claim 28, wherein the membrane is asymmetrical with a non-porous polyimide film on a porous layer.
  30. The gas separation membrane of claim 28 or 29, wherein the membrane has the shape of a hollow fibre.
  31. A method for separating a gas mixture, comprising contacting the mixture with a gas separation membrane according to any one of claims 28 to 30 and applying a pressure difference across the gas separation membrane to effect permeation of at least one component of the gas mixture through the gas separation membrane.
  32. A gas separation device, comprising the gas separation membrane according to any one of claims 28-30.
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