CN114716709B

CN114716709B - Preparation method of polystyrene ion exchange membrane

Info

Publication number: CN114716709B
Application number: CN202210631793.1A
Authority: CN
Inventors: 汪权波; 陈海风; 吴生强
Original assignee: Jiangsu Lu'an Qingfeng New Material Co ltd
Current assignee: Jiangsu Lu'an Qingfeng New Material Co ltd
Priority date: 2022-06-07
Filing date: 2022-06-07
Publication date: 2022-08-23
Anticipated expiration: 2042-06-07
Also published as: CN114716709A

Abstract

The invention discloses a preparation method of a polystyrene ion exchange membrane, which comprises the following steps: (1) preparing 4- (3, 5-dibromomethyl) phenoxystyrene; (2) preparing a chain transfer agent 2- (phenethylthiocarbonate) isobutyric acid; (3) carrying out reversible addition-fragmentation chain transfer polymerization on 4- (3, 5-dibromomethyl) phenoxystyrene and fluorine-containing styrene serving as monomers by taking 2- (phenethyl trithiocarbonate) isobutyric acid as a chain transfer agent to prepare a copolymer, and carrying out quaternization reaction to obtain a polystyrene ion exchange membrane; the AEMs have pendant quaternary ammonium salts separated from the main chain by phenoxy groups, which can reduce OH ^‑ The hydrolysis of the main chain improves the alkali resistance of AEMs; in addition, the side group structure of the dication structure improves the IEC of the membrane, is beneficial to self-assembly of quaternary ammonium salt into an effective ion channel, combines the advantages of long-side chain type and dense functional anion exchange membranes, and has good potential application prospect.

Description

Preparation method of polystyrene ion exchange membrane

Technical Field

The invention belongs to the technical field of fuel cell materials, and particularly relates to a preparation method of a polystyrene ion exchange membrane.

Background

Alkaline Anion Exchange Membrane Fuel Cells (AEMFCs) are considered to be one of the most promising fuel cells because they have the advantages of a wide range of fuel selection, low manufacturing cost, low fuel permeability, and the like. Anion Exchange Membranes (AEMs) are used as core components of AEMFCs, and the performance of the AEMs directly determines the future development prospect of the AEMFCs. AEMs with excellent performance must possess high ionic conductivity and good alkali-resistance/dimensional stability, however, high ionic conductivity usually requires high Ion Exchange Capacity (IEC), which tends to result in membranes with high water absorption and swelling capacity, and in severe cases, AEMs are cracked. Therefore, how to obtain AEMs having both high ionic conductivity and excellent dimensional stability is one of the difficulties faced so far.

In the prior art, AEMs taking quaternary ammonium salts as ionic groups are most widely researched, and polyether ketone, polyether sulfone and polybenzimidazole are mostly taken as polymer frameworks, and the polymer main chains all have aromatic rings, so that the rigidity is high, and the structural stability of the AEMs can be endowed. However, by observing the degradation of the AEMs skeleton under alkaline conditions in different systems, it was found that the alkali stability of the following backbones with pendant trimethylammonium groups was from high to low: polystyrene>Polyphenylene ether>Polysulfones, since hetero atoms in the polymer main chain are susceptible to cations and thus to OH groups ^- Of the attack (c). (Zhao Chong Fu, Liu Wei, Zhang Chun Qing, Cheng Ping, Bai Zhen Min, Shi Yue, preparation, structure and Property of anion exchange Membrane of high Performance hydrogenated Star-shaped Poly (styrene-b-butadiene-b-styrene) Block copolymer [ J]Application chemistry, 2019,36(10): 1135-1146). In addition, when quaternary ammonium groups are far away from the polymer skeleton or a microphase separation structure exists in the polymer, the alkali resistance stability of the AEMs can be obviously improved. Furthermore, the development of cationic side chains containing multiple positive charges (charged groups away from each other without changing the ion exchange capacity) also contributes to the increase in chemical stability of the polymer backbone. Currently, the prior art does not have a polystyrene ion exchange membrane that meets the above requirements.

Disclosure of Invention

According to the defects of the prior art, the technical problems to be solved by the invention are as follows: how to improve the alkali resistance of the polystyrene ion exchange membrane.

The polystyrene ion exchange membrane provided by the invention is designed and synthesized to prepare AEMs by reversible addition fragmentation chain transfer polymerization of a dicationic polystyrene monomer and fluorine-containing polystyrene. The polystyrene monomer containing dications not only has dications, improves the density of unit cations to effectively construct an ion channel, but also enlarges the distance between the cations and the main chain of the polymer, reduces the influence on the hydrophilicity of the main chain, improves the prior polystyrene anion exchange membrane to a certain extent, and improves the alkali resistance and the conductivity of the polystyrene anion exchange membrane.

The reaction flow and the preparation method of the polystyrene ion exchange membrane are as follows:

1. preparation of 4- (3, 5-dibromomethyl) phenoxystyrene (BBS)

4- (3, 5-dimethyl) phenoxy styrene is prepared by nucleophilic substitution of 4-fluoro styrene and 3, 5-dimethylphenol by using potassium carbonate as a catalyst and N, N-dimethylformamide as a solvent.

The feeding molar ratio of the 4-fluorostyrene to the 3, 5-dimethylphenol is 1: 1.

1, 2-dichloroethane is used as a solvent, benzoyl peroxide is used as an initiator, N-bromosuccinimide is used as a brominating agent, and 4- (3, 5-dimethyl) phenoxyl styrene is subjected to bromination reaction to prepare the 4- (3, 5-dibromomethyl) phenoxyl styrene, and has a structure of a formula (II):

（II）

the feeding molar ratio of the 4- (3, 5-dimethyl) phenoxystyrene to the N-bromosuccinimide to the benzoyl peroxide is 1:2: 0.1.

2. Preparation of 2- (phenethyltrithiocarbonate) isobutyric acid (TCIA)

Adding 2-mercaptoisobutyric acid into an alkaline aqueous solution, dropwise adding carbon disulfide, stirring at room temperature for 5 hours, adding benzyl bromide, reacting at 80-90 ℃ for 8 hours, and performing rotary evaporation and column chromatography purification on the reaction solution to obtain an orange-yellow product TCIA.

The alkaline aqueous solution is an aqueous solution dissolved with potassium hydroxide or sodium hydroxide and having a pH = 8-10.

The 2- (phenethyl trithiocarbonate) isobutyric acid is a reversible addition-fragmentation chain transfer polymerization chain transfer agent and has the following molecular structure:

(III)

3. preparation of copolymers by reversible addition-fragmentation chain transfer polymerization

Weighing 2- (phenethyl trithiocarbonate) isobutyric acid (TCIA), BBS, fluorine-containing styrene, azodiisobutyronitrile and a solvent, putting the materials into a reaction bottle, performing three freezing-unfreezing cycles, polymerizing in an oil bath at 70-90 ℃, quenching the reaction by using liquid nitrogen, precipitating in glacial ethyl ether or methanol, and performing suction filtration, washing and drying to obtain the copolymer.

The solvent may be N, N-dimethylformamide, toluene, N-methylpyrrolidone.

The fluorine-containing styrene is 2,3,4,5, 6-pentafluorostyrene or p-trifluoromethylstyrene.

The feeding molar ratio of the BBS to the fluorine-containing styrene is 1 (2 or 4).

4. Preparation of Dicationic polystyrene ion exchange Membrane

N, N-dimethylformamide is taken as a solvent, the copolymer reacts with tertiary amine to prepare the dication polystyrene ion exchange membrane, reaction liquid is filtered and poured into a glass plate, the glass plate is placed in a vacuum drying oven for drying, and finally the membrane is soaked in sodium hydroxide solution for ion exchange and then is stored in deionized water.

The tertiary amine compound is one or more selected from trimethyl tertiary amine aqueous solution and N, N, N ', N' -tetramethyl-1, 4-butanediamine.

The invention has the following advantages and beneficial effects:

(1) compared with AEMs of the polysulfone polymer main chain, the polystyrene ion exchange membrane prepared by the invention has better alkali resistance, on one hand, the polymer main chain does not contain heteroatoms, and on the other hand, the hydrophobic property of the main chain is less influenced by increasing the distance between cations and the main chain.

(2) The polystyrene ion exchange membrane provided by the invention can form an obvious microphase separation structure, increases the distance between cations and a main chain to ensure that the degree of freedom of quaternary ammonium salt ions is higher, and is favorable for separating hydrophilic cations and a hydrophobic main chain to construct an effective ion channel.

Drawings

FIG. 1 is an AFM phase plot of AEMs prepared in example 6.

FIG. 2 is a graph of conductivity as a function of time for AEMs prepared in example 6 in 2mol/L potassium hydroxide solution at 60 ℃.

Detailed Description

The present invention will be described in further detail with reference to specific examples, which are not intended to limit the present invention in any manner. Reagents, methods and apparatus used in the present invention are conventional in the art unless otherwise indicated.

Gel Permeation Chromatography (GPC): the molecular weight of the copolymer is tested by a WATERS 515 type gel permeation chromatograph at normal temperature by taking N, N-dimethylformamide as a solvent and narrow distribution linear polystyrene as a standard sample.

Water content (WU) and Swelling Ratio (SR) test: cutting 1cm × 4cm film, soaking in 80 deg.C deionized water for 24 hr, and measuring wet film mass m _w And length l _w Drying the film at 60 ℃ in vacuum to constant weight, and measuring the mass m of the dry film _d And length l _d Calculating the value of WU or SR according to:

ion Exchange Capacity (IEC) test: the completely dry sample film, determined by Mohr titration, is weighed as W _dry Immersing in 1 mol/L NaCl solution at room temperature for 24h for ion exchange, taking out the membrane, and washing with deionized water to remove free Cl ^- Then the film was immersed in 0.5 mol/L Na ₂ SO ₄ Ion exchange is carried out in the aqueous solution for 24h to completely release Cl ^- . Then with K ₂ CrO ₄ As an indicator, 0.01 mol/L AgNO was used ₃ The solution was titrated with an aqueous solution. The IEC value is calculated according to the following formula:

and (3) ion conductivity test: the impedance of the anion exchange membrane is measured by using a Princeton Versa STAT 4 electrochemical comprehensive test system, and the frequency range is 1 MHz-1 Hz. The ionic conductivity (σ, mS/cm) of the membrane at 80 ℃ was calculated according to the following formula

Wherein L is the distance between two copper electrodes, cm; a denotes the cross-sectional area of the membrane between the two electrodes, cm ² (ii) a R is the resistance value of the film, K omega.

Alkali resistance test: the membrane was immersed in 2mol/L potassium hydroxide solution at 60 ℃ and sampled at intervals to determine the ionic conductivity of the membrane.

And (3) testing mechanical properties: the tensile strength and elongation at break of the sample films were tested using an Instron model 3343 universal tester. The test conditions were: the film was soaked in deionized water for 24 hours at room temperature at a draw rate of 0.2 mm/s before testing.

Example 1

Preparation of 4- (3, 5-dibromomethyl) phenoxystyrene (BBS).

In a three-necked flask equipped with a reflux condenser, a mechanical stirrer and a nitrogen blanket, 20.05 g (0.16mol) of 4-fluorostyrene, 20.22 g (0.16mol) of 3, 5-dimethylphenol, 16.57 g (0.16mol) of potassium carbonate and 200mL of N, N-Dimethylformamide (DMF) were charged. Stirring until the raw materials are completely dissolved, heating to 100 ℃ for reaction for 10 h, and pouring the milky turbid liquid into water for sedimentation to obtain a crude product. Washing with deionized water 5 times to remove potassium carbonate and solvent DMF gave 4- (3, 5-dimethyl) phenoxystyrene.

Respectively adding 18.56g (82.7 mmol) of 4- (3, 5-dimethyl) phenoxystyrene and 200mL of dichloroethane into a three-neck flask provided with a reflux condenser tube, a mechanical stirrer and a nitrogen atmosphere protection device, heating to 60 ℃, stirring to completely dissolve a polymer, cooling to room temperature, respectively adding 2.01g (8.27 mmol) of benzoyl peroxide and 29.54g (166 mmol) of N-bromosuccinimide into the three-neck flask, heating to 80 ℃, reacting for 5 hours, pouring a reaction solution into ethanol, precipitating to obtain a white solid, washing for 5 times by using the ethanol, and drying in a vacuum oven at 100 ℃ for 12 hours to obtain the 4- (3, 5-dibromomethyl) phenoxystyrene.

Example 2

Preparation of chain transfer agent 2- (phenethyl trithiocarbonate) isobutyric acid (TCIA)

500 mL of an aqueous potassium hydroxide solution having pH =8 was prepared, 2.12g (17.64 mmol) of 2-mercaptoisobutyric acid was added thereto, and after stirring uniformly, 1.42g (18.65 mmol) of carbon disulfide was added dropwise, and after stirring at room temperature for 5 hours, the temperature was raised to 85 ℃ and 2.95g (17.25 mmol) of benzyl bromide was added and the reaction was stirred for 8 hours. The reaction solution is decompressed and distilled to remove the solvent, and methylene dichloride is taken as a washing and dehydrating machine and is filtered by a column to obtain an orange-yellow product.

Example 3

Random copolymer P (BBS-co-PFS) was prepared.

Weighing 2- (phenethyl trithiocarbonate) isobutyric acid (TCIA), BBS and Azobisisobutyronitrile (AIBN) and placing the mixture into a reaction bottle, performing three freezing-thawing cycles, injecting and adding 2,3,4,5, 6-Pentafluorostyrene (PFS) and N-methylpyrrolidone (NMP), polymerizing for 18 h in an oil bath at 80 ℃, then quenching with liquid nitrogen, precipitating in methanol with three times of volume, performing suction filtration, washing filter residue with methanol for 3 times, and placing in a vacuum oven at 90 ℃ for drying for 24h to obtain P (BBS-co-PFS).

The amounts and numbers of the reactants are shown in Table 1.

TABLE 1

Numbering	m(TCIA),g	m(BBS),g	m(PFS),g	m(AIBN),g	V(NMP),mL	Mn,g/mol
							C1	0.05	3.07	6.23	0.01	10	52120
C2	0.05	4.14	4.20	0.01	10	48560

Example 4

Random copolymer P (BBS-co-TFS) was prepared.

The material charge of each reactant is as follows: 0.05g TCIA, 2.67g BBS, 4.82g p-Trifluoromethylstyrene (TFS), 0.01g AIBN, 10mL NMP. The sample was designated C3, and Mn was 57654 g/mol.

The reaction procedure was the same as in example 3.

Example 5

Block copolymer P (BBS-b-PFS) was prepared.

Weighing TCIA, BBS and Azobisisobutyronitrile (AIBN), putting into a reaction bottle, performing three times of freezing-unfreezing cycles, injecting NMP, polymerizing for 18 hours in an oil bath at 80 ℃, continuing injecting PFS, keeping the temperature for reaction for 24 hours, quenching the reaction by using liquid nitrogen, pouring the mixed solution into methanol with the volume of 3 times for precipitation, performing suction filtration, washing filter residue for 3 times by using methanol, and drying in a vacuum oven at 90 ℃ for 24 hours to obtain P (BBS-b-PFS).

The feeding amount of each reactant is as follows: 0.06g TCIA, 3.2g BBS, 6.5g 2,3,4,5, 6-Pentafluorostyrene (PFS), 0.01g AIBN, 10mL NMP. The sample was designated B1, and Mn was 45650 g/mol.

Example 6

Preparing the dication polystyrene ion exchange membrane.

Adding the copolymer prepared in the example 3-5 and N, N-Dimethylformamide (DMF) into a flask provided with a constant-pressure dropping funnel and a mechanical stirrer, heating to 80 ℃, stirring to fully dissolve the copolymer, starting to dropwise add a DMF solution (20 wt%) of N, N, N ', N' -tetramethyl-1, 4-butanediamine, and carrying out heat preservation reaction for 12 hours after dropwise adding; adding a metered trimethylamine aqueous solution (33 wt%) into a reaction bottle, preserving heat, refluxing for 24h, finishing the reaction, filtering the reaction solution by using a PTFE filter head with the aperture of 0.45 mu m, pouring the reaction solution on a glass plate, placing the glass plate on a vacuum drying oven at 60 ℃ for drying for 24h, finally soaking the obtained membrane in 1 mol/L sodium hydroxide solution for ion exchange for 24h, and storing the membrane in deionized water to obtain the dicationic polystyrene ion exchange membrane.

The feed ratio of each reactant and the results of the performance test are shown in Table 2.

TABLE 2

Numbering	m (copolymerization) Thing), g	m (N, N, N ', N' -tetramethyl) 1, 4-butanediamine radical), g	m (trimethylamine) Aqueous solution), g	WU，%	SR，%	IEC， mmol/g	Ion conductance Rate, mS/cm	High tensile strength Degree, MPa	Elongation at break,%
										C1-80%	2.42	0.24	0.09	46.5	11.4	1.78	78.8	39.2	15.4
C1-60%	2.14	0.16	0.13	48.7	15.8	1.82	85.4	27.6	26.5
										C1-30%	2.23	0.08	0.24	49.4	24.5	1.80	89.2	15.4	33.8
C2-30%	2.06	0.12	0.33	62.8	22.3	2.59	98.6	29.4	22.9
										C3-60%	2.05	0.15	0.13	51.2	17.4	1.75	83.8	24.8	27.3
B1-60%	2.18	0.16	0.13	53.6	21.9	1.85	91.6	27.4	33.7

Number A of each sample in Table 2 _X Specific meanings of-Y% are: a. the _X A sample number representing the copolymer from which the film was prepared; y% represents the molar amount of benzyl bromide participating in the crosslinking reaction in the copolymer, reflecting the charged molar ratio of N, N, N ', N' -tetramethyl-1, 4-butanediamine to the copolymer, in the case of C1-80%: the input mass of N, N '-tetramethyl-1, 4-butanediamine =2.42 ÷ theoretical repeat unit Mn × 80% × N, N' -tetramethyl-1, 4-butanediamine Mn =2.42 ÷ (382.1 +194.1 × 4) × 80% + 144.26=0.24 g.

From the test results in table 2, it can be seen that the combination of the properties of C1 is the best among the three films of the C1 series, the higher the degree of crosslinking, the higher the tensile strength of the film, the lower the elongation at break, and the lower the swelling rate, and the too strong the rigidity of the film when the degree of crosslinking is 80%, i.e., 80% mole amount of benzyl bromide is crosslinked with the di-functional tertiary amine; when the degree of crosslinking is 30%, the swelling ratio of the film becomes too high. The performance results of C1-60% and C3-60% are similar, and C1-60% using PFS as comonomer has lower water content, higher ionic conductivity and mechanical strength than C3-60% using TFS, because PFS has a larger hydrophobic effect on the polymer backbone, resulting in a higher degree of microphase separation. The cross-linking density of the C1-60% is similar to that of the C2-30%, but the unit cation content of the film is higher, so the mechanical properties of the C1-60% are similar to those of the film, but the C2-30% has higher water content, IEC and ionic conductivity; referring to the AFM phase diagrams of both of FIG. 1, C2-30% of the black regions (hydrophilic regions) were more extensive and the results were consistent. Compared with B1-60%, the C1-60% is a random copolymer, and the B1-60% is a block copolymer, and the performance of the two is similar from the viewpoint of each test result. The swelling rate of the C1-60% compared with the B1-60% in unit water content is lower, which shows that the C1-60% has better dimensional stability; but the ionic conductivity of B1-60% is higher under the condition of similar IEC of the two compounds; and B1-60% has higher elongation at break. The reason is that the hydrophilic and hydrophobic blocks are more beneficial to inducing microphase separation during polymer molding, the larger the area of a micro-region is, so that ion conduction is facilitated, but the influence on the macroscopic size of the membrane after water absorption is larger, and the result is consistent with the AFM test result.

Claims

1. The preparation method of the polystyrene ion exchange membrane is characterized by comprising the following steps:

(1) preparation of 4- (3, 5-dibromomethyl) phenoxystyrene (BBS)

4- (3, 5-dimethyl) phenoxy styrene is prepared by nucleophilic substitution of 4-fluoro styrene and 3, 5-dimethylphenol by using potassium carbonate as a catalyst and N, N-dimethylformamide as a solvent; brominating 4- (3, 5-dimethyl) phenoxy styrene to obtain 4- (3, 5-dibromomethyl) phenoxy styrene;

the 4- (3, 5-dibromomethyl) phenoxystyrene has a structure of formula (II):

（II）

(2) preparation of chain transfer agent 2- (phenethyl trithiocarbonate) isobutyric acid (TCIA)

Adding 2-mercaptoisobutyric acid into an alkaline aqueous solution, dropwise adding carbon disulfide, stirring at room temperature for 5 hours, adding benzyl bromide, reacting at 80-90 ℃ for 8 hours, and performing rotary evaporation and column chromatography purification on the reaction solution to obtain TCIA;

the 2- (phenethyl trithiocarbonate) isobutyric acid has the structure of formula (III):

(III)

(3) preparation of copolymers by reversible addition-fragmentation chain transfer polymerization

TCIA is taken as a chain transfer agent, BBS and fluorine-containing styrene are taken as monomers, azobisisobutyronitrile is taken as an initiator to carry out reversible addition-fragmentation chain transfer polymerization to prepare a copolymer,

(4) preparation of Dicationic polystyrene ion exchange Membrane

N, N-dimethylformamide is taken as a solvent, the copolymer reacts with tertiary amine to prepare the dicationic polystyrene ion exchange membrane, reaction liquid is filtered and poured into a glass plate, the glass plate is placed in a vacuum drying oven for drying, and finally the membrane is soaked in sodium hydroxide solution for ion exchange and then is stored in deionized water.

2. The method for preparing a polystyrene ion exchange membrane according to claim 1, wherein the alkaline aqueous solution in the step (2) is an aqueous solution dissolved with potassium hydroxide or sodium hydroxide and having a pH = 8-10.

3. The method for preparing a polystyrene ion-exchange membrane according to claim 1, wherein the fluorine-containing styrene of step (3) is 2,3,4,5, 6-pentafluorostyrene or p-trifluoromethylstyrene.

4. The method for preparing a polystyrene ion-exchange membrane according to claim 1, wherein the tertiary amine compound in step (4) is trimethyl tertiary amine aqueous solution or N, N, N ', N' -tetramethyl-1, 4-butanediamine or a mixture thereof.