CN111918712A

CN111918712A - Functionalized polyimides and membranes for gas separation

Info

Publication number: CN111918712A
Application number: CN201880090336.8A
Authority: CN
Inventors: 房建华; 刘蕊; 姜金华; 冯兢
Original assignee: Evonik Shanghai Investment Management Co Ltd
Current assignee: Evonik Shanghai Investment Management Co Ltd
Priority date: 2018-02-28
Filing date: 2018-02-28
Publication date: 2020-11-10
Also published as: WO2019165597A1

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 present invention, a gas separation device comprising the gas separation membrane of the present invention, and a method of separating a gas mixture. Gas separation membranes prepared from functionalized polyimides can provide better selectivity and better permeability for separating gas mixture compositions.

Description

Functionalized polyimides and membranes for gas separation

Technical Field

The present invention relates to functionalized polyimides, high performance polyimide membranes for gas separation and general processes for the chemical modification of aromatic polyimides.

Background

Polymeric membranes are used in gas separation because they allow gas separation with low energy consumption and without the use of absorbents. The performance of a polymeric membrane in a gas separation process depends on the gas permeability of the membrane and the permselectivity of the components of the gas mixture. However, there is a trade-off between permeability and selectivity, since membranes with high permeability generally have low selectivity and vice versa (L.M.Robeson, J.Membrane Sci.320(2008) 390-. It is very difficult to further improve the gas separation performance of the membrane (break the upper border of Robeson).

Polyimides are useful in the preparation of polymeric gas separation membranes because they can provide high mechanical stability (allowing use at high gas pressures) and a combination of permeability and selectivity that approaches the upper boundary of the membrane performance Robeson. The properties of polyimide gas separation membranes are typically tailored by the selection of dianhydride and diamine structural units of the polyimide and the use of mixtures of dianhydride and diamine structural units, i.e., by modifying the monomers used to make the polyimide.

M.D. Guiiver and colleagues (Journal of Polymer Science: Part A: Polymer Chemistry, Vol.40,4193-4204(2002)) reported a bromination method of commercially available polyimide Matrimid, which had a gas permeability coefficient higher by about 60% and a slightly decreased selectivity.

Recently, Jong Suk Lee and colleagues (Journal of Membrane Science 545(2018) 358-. Although they further reported that heat treatment of the brominated polyimide (360 ℃) caused a significant increase in the gas permeability coefficient (150-. In addition, 6FDA is an extremely expensive dianhydride monomer compared to other dianhydrides, making it less useful in industrial applications.

K.okamoto et al, polymer.j.30 (1998)492-498 describes the functionalization of polyimides prepared by brominating benzylmethyl groups with 3,3',4,4' -biphenyltetracarboxylic dianhydride (BPDA) and 2,4, 6-trimethyl-1, 3-phenylenediamine (TrMPD) and reacting the resulting benzylbromide groups with trimethyl phosphite or triethyl phosphite to provide polyimides functionalized with phosphonate groups. The functionalized polymer is crosslinked by heating or reaction with 1, 2-diaminoethane. The functionalized and crosslinked polymer provides improved selectivity without decreasing permeate flux when separating benzene and cyclohexane mixtures by pervaporation.

JPH9-173801 describes a method for preparing a gas separation membrane by brominating alkyl groups of an alkyl substituted polyimide, preparing a membrane from the resulting brominated polyimide, and treating the brominated polyimide membrane with a vapor or aqueous solution of ammonia, a primary amine or a secondary amine. An alternative method is described in paragraph [0023], in which the brominated polyimide is reacted in solution with a secondary amine (such as diethanolamine or morpholine) to give an amine-modified polyimide, and then a membrane is prepared by coating or casting a solution of the amine-modified polyimide on a substrate. Amine-modified polyimide membranes exhibit increased selectivity in gas separations but significantly reduced permeability compared to unmodified polyimide membranes.

Disclosure of Invention

The object of the present invention was to develop a general process by means of which polyimide membranes with a significantly enhanced gas permeability coefficient and good selectivity can be produced simultaneously.

The present inventors have now found that an imide functionalized polyimide can be prepared by brominating an aromatic polyimide containing a benzyl group and reacting the resulting brominated polyimide with a cyclic imide salt, preferably an alkali metal salt of a cyclic imide. The present inventors have also discovered that gas separation membranes prepared from such imide functionalized polyimides can provide better selectivity and good permeability for separating gas mixtures than the original polyimides.

The subject of the present invention is therefore a process for preparing functionalized polyimides, comprising the following steps:

a) providing a solution of a polyimide having a repeating unit (I)

Wherein each R is^AIndependently of one another, are aromatic dianhydride monomer units, each R^BAre independently of each other an aromatic diamine monomer unit, and the aromatic diamine monomer unit R^BAt least a portion of (a) comprises one or more methyl groups on the aromatic ring;

b) reacting or photoinitiating the solution of step a) with a brominating agent and an initiator to convert at least part of the methyl groups to brominated methylene groups to provide a brominated polyimide, the degree of bromination preferably being 20% to 150%, such as 20% to 140%, 20% to 130%, more preferably 20% to 120%, even more preferably 30% to 75%;

c) providing a solution of the 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 brominated methylene groups to imidomethylene (imidomethyl) groups.

The imidomethylene group is formed by the reaction of the imidoanionic group of the cyclic imide salt with the brominated methylene group of the brominated polyimide.

In some embodiments, at least 5 mol%, preferably at least 10 mol%, e.g., from 5 to 100 mol%, from 10 to 99 mol%, from 10 to 95 mol%, from 10 to 90 mol%, from 10 to 85 mol%, from 10 to 80 mol%, from 20 to 100 mol%, from 20 to 99 mol%, from 20 to 95 mol%, from 20 to 90 mol%, from 20 to 85 mol%, from 20 to 80 mol%, from 30 to 100 mol%, from 30 to 99 mol%, from 30 to 95 mol%, from 30 to 90 mol%, from 30 to 85 mol%, from 30 to 80 mol% of the brominated methylene groups in step d) are converted to imidomethylene groups.

The polyimide of step a) can be used for the preparation of gas separation membranes. However, the gas separation membrane prepared from the polyimide of step a) has a lower gas separation efficiency than the functionalized polyimide obtained in step d).

According to conventional methods (e.g. elemental analysis and/or¹H NMR spectroscopy, typically elemental analysis), the degree of bromination can be determined.

The mol% conversion of brominated methylene groups to imidomethylene groups can be determined according to elemental analysis methods.

As used herein, a cyclic imide is an imide that comprises two acyl groups bound to a nitrogen atom, where the two carbonyl carbons are connected by a substituted or unsubstituted carbon chain or a substituted or unsubstituted aromatic group. As used herein, a cyclic imide salt is a tertiary amine salt formed from the cyclic imide.

The cyclic imide salt is preferably an alkali metal salt of a cyclic imide, more preferably a potassium or sodium salt of a cyclic imide. The cyclic imide salts may have the following general structure (II):

wherein Ar represents:

each R₁To R₆Independently of one another, hydrogen, or C which is unsubstituted or substituted by one or more halogen radicals, such as fluorine, chlorine and bromine radicals₁To C₄An alkyl group; c₁To C₄The alkyl group is preferably selected from-CH₃、-CF₃、-CH(CH₃)₂and-C (CH)₃)₃(ii) a And M⁺Denotes a metal ion, preferably an alkali metal ion, especially K⁺Or Na⁺。

When the cyclic imide salt contains a naphthalene ring, it is preferably unsubstituted on the naphthalene ring. When the cyclic imide salt contains a benzene ring, it preferably contains no or only one alkyl substituent group on the benzene ring.

Examples of the cyclic imide salt may be selected from alkali metal alpha-methyl-alpha-phenyl succinimide salt, alkali metal phthalimide salt or alkali metal salt of naphthalene 1, 8-dicarboxylic acid imide.

Further subjects of the present invention are functionalized polyimides obtainable by this process, gas separation membranes comprising the functionalized polyimides of the invention, gas separation devices comprising the gas separation membranes of the invention and processes for separating a gas mixture comprising contacting the gas mixture with the gas separation membranes of the invention and applying a pressure differential across the gas separation membranes to effect permeation of at least one component of the gas mixture through the gas separation membranes.

Preferably, the polyimide is a polymer of structure (III)

Wherein the aromatic dianhydride monomer unit R^AIndependently of one another, selected from:

the aromatic diamine monomer unit R^B1Independently of one another, selected from:

wherein: each R¹To R⁷Independently of one another, is hydrogen or a methyl group, with the proviso that R¹To R³At least one of which is different from hydrogen, and R⁴To R⁷At least one of which is different from hydrogen;

R⁸is hydrogen or C which is unsubstituted or substituted by one or more halogen radicals, e.g. fluorine, chlorine and bromine radicals₁To C₃An alkyl group, preferably hydrogen or methyl;

and the aromatic diamine monomer unit R^B2Independently of one another, selected from:

and x is 0.1 to 1, e.g., 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 unit R^B1Independently of one another, selected from:

and x is 1.

In some embodiments, the aromatic dianhydride monomer unit R^AIndependently of one another, selected from:

in some embodiments, the polyimide is a polymer, particularly a block copolymer of structure (IV)

Wherein the aromatic dianhydride monomer unit R^A1Independently of one another, selected from:

the aromatic diamine monomer unit R^B3Independently of one another, selected from:

the aromatic dianhydride monomer unit R^A2Independently of one another, selected from:

and the aromatic diamine monomer unit R^B4Independently of one another, selected from:

wherein: each R¹To R⁷Independently of one another, is hydrogen or a methyl group; r⁸As described above;

y is a number of from 5 to 500,

z is from 5 to 500, and

R^A1is different from R^A2，R^B3Is different from R^B4Or R^A1Are all different from R^A2，R^B3Is different from R^B4。

In some embodiments, R of the above polyimides^B4Selected from:

as used herein, the term "functionalized polyimide" refers to a polyimide that is functionalized with a cyclic imide salt of a brominated polyimide, unless specifically stated otherwise.

The present invention provides a technical process for producing a functionalized polyimide having significantly improved gas separation performance. It involves bromination of a methyl-substituted diamine-derived polyimide in the first step and functionalization with a cyclic imide salt in the next step. The bromination reaction may be carried out by heating or photoinitiating a solution mixture containing the polyimide, brominating agent, and initiator. And carrying out next-step functionalization on the methylene bromide group and the cyclic imide salt of the obtained brominated polyimide to obtain the required product. The original polyimide is a polyimide having a repeating unit (I), preferably a polymer of structure (III).

In some embodiments, a method of preparing a functionalized polyimide comprises the steps of:

A) dissolving polyimide (preferably polymer with structure (III)) with a repeating unit (I) in an organic solvent, adding a brominating agent and an initiator, and reacting at 60-120 ℃ for 0.5-24 hours, preferably at 70-100 ℃ for 2-10 hours to obtain brominated polyimide; wherein the molar ratio of the methyl group of the polyimide to the brominating agent is controlled to be 20-1: 1; and

B) the brominated polyimide is dissolved in an organic solvent, usually under a nitrogen atmosphere, a cyclic imide salt is added, and reacted at 30 to 120 ℃ for 1 to 60 hours, for example, 2 to 60 hours, 2 to 48 hours, 2 to 36 hours, 2 to 24 hours, or 1 to 24 hours, to obtain a functionalized polyimide.

In some embodiments, the reaction of step b) is carried out at 60-120 ℃ for 0.5-24 hours, preferably 70-100 ℃ for 2-10 hours.

In some embodiments, the reaction of step d) is carried out at 30-120 ℃ for 1-60 hours, such as 2-60 hours, 2-48 hours, 2-36 hours, 2-24 hours, or 1-24 hours.

In some embodiments, the molar ratio between the brominated polyimide and the cyclic imide salt is from 1:0.05 to 1:5, preferably from 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 into an insoluble organic liquid (non-solvent), such as methanol, and the resulting precipitate is collected by filtration, washed thoroughly with the insoluble organic liquid and dried in vacuo to yield brominated polyimide.

In some embodiments, the reaction product obtained in step (b) is cooled to room temperature, then the solution mixture is poured into an insoluble organic liquid (e.g., methanol), the resulting precipitate is collected by filtration, washed thoroughly with deionized water, and dried in a vacuum oven to give a functionalized polyimide.

The methyl group of the above polyimide is readily brominated by reaction with a conventional brominating agent such as N-bromosuccinimide (NBS), dibromoisocyanuric acid and 1, 3-dibromo-5, 5-dimethylhydantoin in the presence of an initiator such as Benzoyl Peroxide (BPO). The degree of bromination can be controlled by controlling the reaction conditions, for example, at a temperature of 60 to 120 deg.C, a reaction time of 0.5 to 24 hours, and a molar ratio of methyl group to brominating agent (e.g., NBS) of 20 to 1: 1.

The methyl group of the above polyimide is readily brominated by reaction with conventional brominating agents such as N-bromosuccinimide (NBS), dibromoisocyanuric acid, and 1, 3-dibromo-5, 5-dimethylhydantoin in the presence of an initiator such as Benzoyl Peroxide (BPO). The degree of bromination can be controlled by controlling the reaction conditions, e.g., at a temperature of 60 to 120 deg.C, for a reaction time of 0.5 to 24 hours, and at a molar ratio of methyl groups to brominating agent (e.g., NBS) of 20 to 1: 1.

Conventional organic solvents, such as 1,1,2, 2-Tetrachloroethane (TCE), chloroform, dichloromethane, N-Dimethylformamide (DMF), N-dimethylacetamide (DMAc), and 1-methylpyrrolidone (NMP), may be used to dissolve the polyimide, depending on their respective chemical structures. After completion of the bromination reaction, the reaction mixture may be poured into an insoluble organic liquid such as methanol, acetone, etc. The precipitate (brominated polyimide) can be collected by filtration and dried in a vacuum oven.

Preferably, the bromination reaction is carried out using 0.3 to 1 equivalent (eq.) of N-bromosuccinimide (NBS) to give a degree of bromination of 30% to 74%. Preferably, 1,1,2, 2-Tetrachloroethane (TCE) and/or N, N-Dimethylamide (DMF) are used as the solvent for the bromination reaction. Preferably, the bromination is carried out at 70-100 ℃ for 2-10 hours.

The above brominated polyimide may be dissolved in a conventional solvent such as dichloromethane, chloroform, 1,2, 2-Tetrachloroethane (TCE) and/or N, N-Dimethylformamide (DMF), N-dimethylacetamide (DMAc), 1-methylpyrrolidone (NMP), etc., to obtain a 1-30 w/v% solution. The cyclic imide salt (e.g., potassium phthalimide) is then added and the mixture is heated at 30-120 ℃ for 1-60 hours, e.g., 2-60 hours, 2-48 hours, 2-36 hours, 1-24 hours, or 2-24 hours. After cooling to room temperature, the solution mixture may be poured into an insoluble organic liquid (e.g., methanol), the resulting precipitate collected by filtration, washed thoroughly with deionized water, and dried in a vacuum oven.

In some embodiments, the potassium salts of phthalimide and naphthalimide are selected to react with the brominated polyimide, for example at 40 ℃ for 24 hours.

In some embodiments, the brominating agent is selected from N-bromosuccinimide, dibromoisocyanuric acid, and 1, 3-dibromo-5, 5-dimethylhydantoin.

In some embodiments, the photoinitiation is achieved by ultraviolet light irradiation.

In some embodiments, the initiator is used by adding an organic peroxide and heating.

In some embodiments, the organic peroxide is a dialkyl peroxide, an alkyl acyl peroxide, or a diacyl peroxide, preferably a diacyl peroxide, more preferably a dibenzoyl peroxide.

In some embodiments, the brominating agent is reacted with the aromatic diamine monomer units R^BThe molar ratio of benzyl groups of (a) is from 0.05 to 1.

In some embodiments, step b) is performed in a chlorinated hydrocarbon solution, preferably in a 1,1,2, 2-tetrachloroethane solution.

In some embodiments, step b) is performed in a carboxylic acid dialkylamide solution, preferably in a solution of N, N-dimethylformamide, N-dimethylacetamide or N-methylpyrrolidone.

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 -phenyl 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 performed in a carboxylic acid dialkylamide solution, preferably in a solution of N, N-dimethylformamide, N-dimethylacetamide or N-methylpyrrolidone.

In some embodiments, wherein step d) is performed at a temperature of 30 to 120 ℃.

In some embodiments, in step b), the brominating agent is N-bromosuccinimide or dibromoisocyanuric acid, and steps c) and d) are performed by adding a sufficient amount of an alkali metal alkoxide to the solution obtained in step b) to convert the succinimide or phthalimide formed in step b) to an alkali metal succinimide salt or an alkali metal phthalimide salt.

Another subject of the present invention is a functionalized polyimide obtainable by the process according to the invention.

Another subject of the invention is a functionalized polyimide, wherein the polyimide is a polymer comprising a random copolymer of structure (III),

wherein: each R¹To R⁷Independently of one another, hydrogen or a radical R^cWith the proviso that R¹To R³At least one of which is different from hydrogen, and R⁴To R⁷At least one of which is different from hydrogen,

R^cis methyl or CH₂R^dGroups, provided however that at least 5 mol%, e.g., 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 the groups R^cIs CH₂R^dGroups, for example, 5-100 mol%, 10-99 mol%, 10-95 mol%, 10-90 mol%, 10-85 mol%, 10-80 mol%, 10-75 mol%, 10-70 mol%, 10-65 mol%, 10-60 mol%, 10-55 mol%, 10-50 mol%, 10-45 mol%, 10-40 mol%, 20-100 mol%, 20-99 mol%, 20-95 mol%, 20-90 mol%, 20-85 mol%, 20-80 mol%, 20-75 mol%, 20-70 mol%, 20-65 mol%, 20-60 mol%, 20-55 mol%, 20-50 mol%, 20-45 mol%, 20-40 mol%, 30-100 mol%, 30-99 mol%, 30-95 mol%, 30-90 mol%, 30-85 mol%, 30-80 mol%, 30-75 mol%, 30-70 mol%, 30-65 mol%, 30-60 mol%, 30-55 mol%, 30-50 mol%, 30-45 mol%, 30-40 mol% of the group R^cIs CH₂R^dThe radical(s) is (are),

R^dis of structure (II'):

wherein Ar represents:

each R₁To R₆Independently of one another, hydrogen, or C which is unsubstituted or substituted by one or more halogen radicals, such as fluorine, chlorine and bromine radicals₁To C₄An alkyl group; c₁To C₄The alkyl group is preferably selected from-CH₃、-CF₃、-CH(CH₃)₂and-C (CH)₃)₃；

It is understood that the non-functionalized polyimide is a polyimide of structure (III), but R^cAre all methyl. In other words, the non-functional polyimides are substituted by R at least in part on the methyl groups^dThe groups are functionalized. Such non-functionalized polyimides can also be used to prepare gas separation membranes. However, gas separation membranes prepared from such non-functionalized polyimides have lower gas separation efficiency than functionalized polyimides of structure (III).

In some embodiments, the aromatic diamine monomer units R of the functionalized polyimides described above^B1Each R in (1)¹To R⁷Is a group R^c。

In some embodiments, in the above functionalized polyimides, x is 1, the aromatic diamine monomer unit R^B1Independently of one another, selected from:

in some embodiments, in the above functionalized polyimides, the aromatic dianhydride monomer units R^AIndependently of one another, selected from:

in some embodiments, in the above-described functionalized polyimides, the polyimides are polymers comprising block copolymers of structure (IV)

wherein: r^cIs methyl or CH₂R^dGroups, provided however that at least 5 mol%, e.g., 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 the groups R^cIs CH₂R^dRadicals, for example, 5 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 10 mol%-60 mol%, 10-55 mol%, 10-50 mol%, 10-45 mol%, 10-40 mol%, 20-100 mol%, 20-99 mol%, 20-95 mol%, 20-90 mol%, 20-85 mol%, 20-80 mol%, 20-75 mol%, 20-70 mol%, 20-65 mol%, 20-60 mol%, 20-55 mol%, 20-50 mol%, 20-45 mol%, 20-40 mol%, 30-100 mol%, 30-99 mol%, 30-95 mol%, 30-90 mol%, 30-85 mol%, 30-80 mol%, 30-75 mol%, 30-70 mol%, 30-65 mol%, 30-60 mol%, 30-55 mol%, 30-50 mol%, 30-45 mol%, 30-40 mol% of the group R.^cIs CH₂R^dThe radical(s) is (are),

R^dis of structure (II'):

wherein Ar represents:

each R₁To R₆Independently of one another, hydrogen, or C which is unsubstituted or substituted by one or more halogen radicals, e.g. fluorine radicals₁To C₄An alkyl group; c₁To C₄The alkyl group is preferably selected from-CH₃、-CF₃、-CH(CH₃)₂and-C (CH)₃)₃；

wherein: each R¹To R⁷Independently of one another, hydrogen or a group R as defined above^c；R⁸As defined above;

y is a number of from 5 to 500,

z is from 5 to 500, and

In some embodiments, R^B4Selected from:

the polyimide polymer of the present invention may be a homopolymer or a copolymer. The kind of the copolymer is not limited, and for example, the copolymer may be an alternating copolymer, a periodic copolymer, a statistical copolymer, a block copolymer, or the like.

The functionalized polyimides of the invention are useful for preparing gas separation membranes.

Another subject of the invention is a gas separation membrane comprising a functionalized polyimide according to the invention.

In some embodiments, the membrane is prepared from the functionalized polyimides of the present invention.

In some embodiments, the membrane is asymmetric to the non-porous polyimide membrane on the porous layer.

In some embodiments, the membrane has the shape of a hollow fiber.

Another subject of the invention is a process for the separation of a gas mixture, which comprises bringing the mixture into contact with a gas separation membrane according to 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.

Another subject of the invention is a gas separation membrane device comprising a gas separation membrane of the invention.

The functionalized polyimide membranes of the present invention exhibit both a significantly enhanced gas permeability coefficient and good selectivity.

The film can be made by conventional methods. For example, the membrane may be fabricated by a solution casting (solution cast) method using a polymer solution of 2-25 w/v%.

The gas permeability coefficient is closely dependent on the polymer fractional free volume (V)_F) And V is_FThe higher the permeability coefficient. As disclosed in the present invention, the introduction of cyclic imide groups in the polyimide structure is an effective method to increase the free volume of the membrane and thus achieve higher permeability. On the other hand, selectivity is closely related to the interaction between the polymer block and the permeant gas molecules. Polymeric membranes that have a high affinity for one permeant and little affinity for another tend to be highly selective. Modified polyimide pairs such as CO by appropriate functionalization as disclosed in the present invention₂And O₂Has a greatly enhanced affinity for gases such as N₂And CH₄The affinity of the gas (a) is lower, resulting in higher or similar selectivity. The membranes made of functionalized polyimides of the invention are particularly suitable for the separation of gases, such as CO₂/N₂、CO₂/CH₄、O₂/N₂。

Through proper chemical modification (bromination and functionalization), the invention grafts functional group groups with high polarity and larger volume into a polyimide framework, and simultaneously, the gas permeability coefficient is greatly enhanced and the selectivity is enhanced.

The process of the present invention is applicable to a wide variety of polyimides having a structure containing methyl groups in the diamine group (polyimides derived from methyl-substituted diamines). The reaction condition is moderate and easy to control.

Other advantages of the invention will be apparent to those skilled in the art upon reading the specification.

Drawings

FIG. 1 shows the results of Fourier transform infrared (FT-IR) spectroscopic analysis of the functionalized polyimide obtained in example 4.

Detailed Description

The invention will now be described in detail by way of the following examples. The scope of the invention should not be limited to the embodiments of the examples.

Analysis program

Tensile strength was measured using a general purpose tensile tester (Instron 4465, a commercially available product from Instron, USA). The sample was 80mm long, 5mm wide, and 30-50 μm thick. The crosshead speed was 2 mm/min.

The gas permeability was measured using a gas solubility and diffusivity tester GTR-1ADFE (available from GTR Tec, Japan). The test was carried out at 35 ℃ and an upstream pressure of 0.1 to 0.4 mPa. The measurement is based on a vacuum time lag method, and the gas permeability coefficient (P) is determined from the steady state permeation flux during a period of 5 to 10 times the time lag (θ). The effective membrane area is 15.2cm²。

The degree of bromination was determined by elemental analysis using an elemental analyzer (Vario EL Cube, germany).

The mol% conversion of brominated methylene groups to imidomethylene groups can also be determined according to elemental analysis methods.

FT-IR was recorded on a Paragon 1000PC FT-IR spectrometer (Perkin Elmer, USA) using a polyimide film.

Example 1: preparation of polyimide BPDA-TrMPD

To a 100mL fully dried three-necked flask, 3.00g of 2,4, 6-trimethyl-1, 3-phenylenediamine (TrMPD) and 60mL of 1-methylpyrrolidone (NMP) were added under a nitrogen purge, and the mixture was continuously stirred at room temperature. Then, 5.88g of 3,3',4,4' -biphenyltetracarboxylic dianhydride (BPDA) was added in portions over 3 hours. After complete addition of BPDA, the reaction mixture was stirred for a further 5 hours. The solution mixture was slowly heated to 80 ℃ and then 20mL of xylene was added via the dropping funnel. The reaction mixture was further heated to 180 ℃ with the slow addition of xylene and held at this temperature for 10 hours. After cooling to room temperature, the highly viscous solution was poured into methanol, and the fibrous precipitate was collected by filtration and finally dried in a vacuum oven at 120 ℃ for 10 hours. The polyimide product is designated BPDA-TrMPD.

Example 2: bromination of polyimide BPDA-TrMPD

1.0g (2.45mmol) of BPDA-TrMPD and 20mL of 1,1,2, 2-Tetrachloroethane (TCE) were placed in a 150mL dry three-necked flask equipped with a condenser. Then, 0.302g (1.72mmol) of N-bromosuccinimide (NBS) and 0.0207g of Benzoyl Peroxide (BPO) were added. The mixture was stirred at 85 ℃ for 6 hours. After cooling to room temperature, the solution mixture was poured into methanol. The precipitate was collected by filtration, washed thoroughly with MeOH, and finally dried under vacuum at 80 deg.f for 10 hours. The brominated polyimide produced is referred to as PI-0.7Br, where "0.7" refers to the molar ratio of NBS to BPDA-TrMPD in the feed. The degree of bromination of this polyimide was calculated to be 59% based on the elemental analysis data. It showed a tensile strength of 72MPa and an elongation at break of 87%.

The results of elemental analysis of the brominated polyimide obtained in example 2 were as follows:

C：65.55％，H：4.17％，N：5.94％，O：13.98％，Br：10.36％。

preparation of brominated BPDA-TrMPD polyimide obtained in example 2 in DMSO-d6¹The H NMR spectrum shows that the methyl groups on the aromatic ring are partially converted to brominated methylene groups and the desired brominated polyimide is obtained.

Example 3: bromination of polyimide BPDA-TrMPD

The procedure was followed except that the molar ratio of NBS to BPDA-TrMPD in the feed was controlled to 0.3:1 to give a brominated polyimide with a degree of bromination of 30%. It showed a tensile strength of 73MPa and an elongation at break of 27%.

The molar ratio of NBS to BPDA-TrMPD in the feed was changed to 0.5:1 and 1:1 to obtain brominated polyimides PI-0.5Br and PI-1.0Br with bromination degrees of 46% and 74%, respectively. The tensile strength and elongation at break of PI-0.5Br were 74MPa and 44%, respectively, and the tensile strength and elongation at break of PI-1.0Br were 73MPa and 80%, respectively.

Example 4: reaction of brominated polyimides with cyclic imide salts

To a 150mL dry three-necked flask equipped with a condenser were added 0.5g of PI-0.7Br and 30mL of TCE. The mixture was stirred continuously to dissolve the solid completely. Then, 0.2g of potassium phthalimide salt was added. The reaction temperature was maintained at 40 ℃ for 24 hours. The mixture solution was directly cast on a clean glass plate and placed in an air-drying oven at 60 ℃ for 8 hours. The membrane was peeled off, thoroughly washed with methanol and water in order, and finally dried in a vacuum oven at 120 ℃ for 10 hours. It showed a tensile strength of 68MPa and an elongation at break of 16%.

Characterization of functionalized polyimides

The results of Fourier transform infrared (FT-IR) spectroscopic analysis of the film prepared by the functionalized polyimide obtained in example 4 are shown in FIG. 1.

Elemental analysis was performed using the functionalized polyimide obtained in example 4. Two tests were performed on this polyimide.

The results of the elemental analysis of the functionalized polyimide obtained in embodiment 4 are as follows:

TABLE 1 results of elemental analysis

Test number	N[％]	C[％]	H[％]	Others (Br + O)
					1	5.80	66.63	4.69	22.88
2	5.86	66.19	4.13	23.82
					Mean value of	5.83	66.38	4.41	23.35

The calculated conversion (mol% of brominated methylene groups converted to iminomethylene groups) was 44% based on carbon and 48% based on other atoms (Br + O).

FT-IR spectroscopy and elemental analysis confirmed that the desired functionalized polyimide was obtained.

Example 5: gas permeability coefficient and selectivity test

A5 w/v% polymer solution in organic solvent (TCE or NMP) was cast onto a glass plate and dried in an air-drying cabinet at 60 deg.C (for TCE) or 80 deg.C (for NMP) for 8 h. The cast film was peeled off from the glass plate and further dried under vacuum at 120 ℃ for 12 hours.

The gas permeability coefficients and the ideal selectivities of the brominated polyimide membranes and the virgin polyimide membranes at 35 ℃ and 100kPa (upstream pressure) are shown in table 2.

TABLE 2 permeation coefficient and Selectivity of membranes

Note: the unit of permeability coefficient is Barrer (1 Barrer-10)^-10cm³*cm/cm²*s*cmHg)。

Example 6: gas permeability coefficient and selectivity test

The gas permeability coefficient and the ideal selectivity of the polyimide membrane modified with potassium phthalimide salt (see example 4) at 35 ℃ and 100kPa (upstream pressure) were determined and are illustrated in table 3. For comparison, the table also shows the data relating to PI-0.7Br and virgin polyimide (BPDA-TrMPD) films. It is evident that the phthalimide potassium salt modified polyimide membranes exhibit significantly enhanced gas permeability coefficients and enhanced selectivity compared to the precursor membrane.

TABLE 3 permeation coefficient and Selectivity of membranes

As used herein, terms such as "comprises," "comprising," and similar terms used herein are open-ended terms that mean "including at least" unless specifically stated otherwise.

All references, tests, standards, documents, publications, etc. mentioned herein are incorporated by reference. If numerical limits or ranges are specified, endpoints are included. Also, all values and subranges within a numerical limit or range are specifically included as if explicitly written out.

The previous description is provided to enable any 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, the present 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, in a broad sense, certain embodiments of the invention may not show all of the benefits of the invention.

Claims

1. A method of preparing a functionalized polyimide, the method comprising the steps of:

a) providing a solution of a polyimide having a repeating unit (I)

Wherein each R is^AIndependently of one another, are aromatic dianhydride monomer units, each R^BIndependently of one another, an aromatic diamine monomer unit, and the aromatic diamine monomer unit R^BAt least a portion of (a) comprises one or more methyl groups on the aromatic ring;

b) reacting or photoinitiating the solution of step a) with a brominating agent and an initiator to convert at least part of the methyl groups to brominated methylene groups to provide a brominated polyimide, preferably having a degree of bromination of from 20% to 150%, such as from 20% to 120%, more preferably from 30% to 75%;

d) reacting the solution of step c) with a cyclic imide salt to convert at least a portion of the brominated methylene groups to imidomethylene groups; in step d), preferably at least 5 mol%, more preferably at least 10 mol% of the brominated methylene groups are converted into imidomethylene groups.

2. The method of claim 1, wherein the cyclic imide salt has structure (II):

wherein Ar represents:

each R₁To R₆Independently of one another, hydrogen, or unsubstituted or monoC substituted by one or more halogen radicals, e.g. fluorine, chlorine and bromine radicals₁To C₄An alkyl group; said C is₁To C₄The alkyl group is preferably selected from-CH₃、-CF₃、-CH(CH₃)₂and-C (CH)₃)₃(ii) a And

M⁺denotes a metal ion, preferably an alkali metal ion, especially K⁺Or Na⁺。

3. The method of claim 1 or 2, wherein the polyimide is a polymer of structure (III)

4. The method of claim 3, wherein the aromatic diamine monomer unit R^B1Independently of one another, selected from:

5. the method of claim 3, wherein the aromatic diamine monomer unit R^B1Independently of one another, selected from:

and x is 1.

6. The method of claim 5, wherein the aromatic dianhydride monomer unit R^AIndependently of one another, selected from:

7. the method of claim 1 or 2, wherein the polyimide is a polymer, in particular a block copolymer of structure (IV)

wherein: each R¹To R⁷As defined above; r⁸As described above;

y is a number of from 5 to 500,

z is from 5 to 500, and

R^A1is different from R^A2，R^B3Is different from R^B4Or R is^A1Are all different from R^A2And R is^B3Is different from R^B4。

8. The method of claim 7, wherein R^B4Selected from:

9. the process according to any one of the preceding claims, wherein the brominating agent is selected from the group consisting of N-bromosuccinimide, dibromoisocyanuric acid, and 1, 3-dibromo-5, 5-dimethylhydantoin.

10. A method as claimed in any preceding claim, wherein the photoinitiation is effected by ultraviolet light irradiation.

11. A process as claimed in any one of claims 1 to 10, wherein the initiator is used by adding an organic peroxide and heating.

12. The process according to claim 11, wherein the organic peroxide is a dialkyl peroxide, an alkyl acyl peroxide or a diacyl peroxide, preferably a diacyl peroxide, more preferably a dibenzoyl peroxide.

13. A process as claimed in any one of the preceding claims wherein the brominating agent reacts with the aromatic diamine monomer units R^BThe molar ratio of benzyl groups of (a) is from 0.05 to 1.

14. The process according to any of the preceding claims, wherein step b) is carried out in a chlorinated hydrocarbon solution, preferably in a 1,1,2, 2-tetrachloroethane solution.

15. The process according to any one of claims 1 to 14, wherein step b) is carried out in a carboxylic acid dialkylamide solution, preferably in a N, N-dimethylformamide, N-dimethylacetamide or N-methylpyrrolidone solution.

16. A process according to 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 alkali metal alpha-methyl-alpha-phenyl succinimide salt, alkali metal phthalimide salt or an alkali metal salt of naphthalene 1, 8-dicarboxylic acid imide.

18. The process according to any of the preceding claims, wherein step d) is carried out in a solution of a carboxylic acid dialkylamide, preferably in a solution of N, N-dimethylformamide, N-dimethylacetamide or N-methylpyrrolidone.

19. The method according to any of the preceding claims, wherein step d) is performed at a temperature of 30 ℃ to 120 ℃.

20. The process according to 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 performed by adding an alkali metal alkoxide to the solution obtained in step b) in an amount sufficient to convert the succinimide or phthalimide formed in step b) into an alkali metal succinimide salt or alkali metal phthalimide salt.

21. A functionalized polyimide obtainable by the process of any one of claims 1 to 20.

22. A functionalized polyimide, wherein the polyimide is a polymer comprising a random copolymer of structure (III)

R^cis methyl or CH₂R^dGroups, but with the proviso that at least 5 mol%, e.g., 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 8 mol%, are provided5 mol%, at least 90 mol% of radicals R^cIs CH₂R^dGroups, for example, 5-100 mol%, 10-99 mol%, 10-95 mol%, 10-90 mol%, 10-85 mol%, 10-80 mol%, 10-75 mol%, 10-70 mol%, 10-65 mol%, 10-60 mol%, 10-55 mol%, 10-50 mol%, 10-45 mol%, 10-40 mol%, 20-100 mol%, 20-99 mol%, 20-95 mol%, 20-90 mol%, 20-85 mol%, 20-80 mol%, 20-75 mol%, 20-70 mol%, 20-65 mol%, 20-60 mol%, 20-55 mol%, 20-50 mol%, 20-45 mol%, 20-40 mol%, 30-100 mol%, 30-99 mol%, 30-95 mol%, 30-90 mol%, 30-85 mol%, 30-80 mol%, 30-75 mol%, 30-70 mol%, 30-65 mol%, 30-60 mol%, 30-55 mol%, 30-50 mol%, 30-45 mol%, 30-40 mol% of the group R^cIs CH₂R^dThe radical(s) is (are),

R^dis of structure (II'):

wherein Ar represents:

each R₁To R₆Independently of one another, hydrogen, or C which is unsubstituted or substituted by one or more halogen radicals, such as fluorine, chlorine and bromine radicals₁To C₄An alkyl group; said C is₁To C₄The alkyl group is preferably selected from-CH₃、-CF₃、-CH(CH₃)₂and-C (CH)₃)₃；

23. The functionalized polyimide of claim 22, wherein each R is¹To R⁷Is a group R^c。

24. The functionalized polyimide of claim 22, wherein x is 1 and the aromatic diamine monomer unit R^B1Independently of one another, selected from:

25. the functionalized polyimide of claim 24, wherein the aromatic dianhydride monomer unit R^AIndependently of one another, selected from:

26. the functionalized polyimide of claim 22, wherein the polyimide is a polymer comprising a block copolymer of structure (IV)

the aromatic diamine monoBody unit R^B3Independently of one another, selected from:

wherein: r^cAs defined above;

R^das defined above;

wherein: each R¹To R⁸As defined above;

y is a number of from 5 to 500,

z is from 5 to 500, and

27. The functionalized polyimide of claim 26, wherein R^B4Selected from:

28. a gas separation membrane comprising the functionalized polyimide of any one of claims 21 to 27.

29. The gas separation membrane of claim 28, wherein the membrane is asymmetric to the non-porous polyimide membrane on the porous layer.

30. The gas separation membrane of claim 28 or 29, wherein the membrane has the shape of a hollow fiber.

31. A method of separating a gas mixture, the method comprising contacting the mixture with a gas separation membrane of any one of claims 28 to 30, and applying a pressure differential 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 membrane device comprising a gas separation membrane according to any one of claims 28 to 30.