Ionic Polymer Membrane Synthesis via Post-Polymerization Modification
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Solution Overview
Problem
Existing methods for producing ionic polymer membranes with multiple ion exchange groups face challenges such as high boiling point monomers, water solubility issues, difficulty in maintaining ion exchange groups, cross-linking problems, and low durability due to impurities and complex synthesis processes.
Innovation Solution
A method involving steps to convert a —SO2F group in a polymer to a pendant group with multiple ion exchange groups, using specific compounds and thermal treatments to prevent cross-linking and achieve high ion exchange capacity and low water uptake, while simplifying the synthesis process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a monomer with multiple ion exchange groups in one pendant group is synthesized and polymerized, then the ionic polymer membrane achieves high ion exchange capacity and low water uptake, but the monomer has high boiling point making purification by distillation difficult
Solution Approach 1:
The patent extracts the multiple ion exchange groups from a single complex monomer structure and instead introduces them through a post-polymerization modification process using compound (a). This avoids the need to synthesize and purify complex monomers with multiple ion exchange groups, while still achieving the desired high ion exchange capacity in the final polymer membrane.
Solution Approach 2:
The patent performs preliminary polymerization to create a polymer backbone first, then subsequently introduces multiple ion exchange groups through reaction with compound (a). This preliminary action of forming the polymer structure before adding functional groups simplifies the overall manufacturing process compared to attempting to create and purify complex functionalized monomers beforehand.
2Reliability
If a monomer with multiple ion exchange groups is used for polymerization, then the polymer membrane achieves high ion exchange capacity, but the monomer is water-soluble and hardly soluble in fluorinated solvents, restricting polymerization methods
Solution Approach 1:
The patent segments the functionalization process from the polymerization process. First, a fluorinated polymer is synthesized using standard fluorinated monomers that are soluble in fluorinated solvents. Then, multiple ion exchange groups are introduced in a separate step through reaction with compound (a). This segmentation allows each process to use appropriate solvents and methods without being constrained by the solubility requirements of the final functionalized structure.
Solution Approach 2:
The patent uses an intermediary compound (a) that reacts with the fluorinated polymer to introduce multiple ion exchange groups. This intermediary approach allows the polymerization to proceed in fluorinated solvents with fluorinated monomers, then transfers the multiple ion exchange functionality through a controlled chemical reaction, bypassing the solubility issues that would arise from using pre-functionalized monomers.
3Stability of the object's composition
If fluorine gas is used to convert unstable polymer terminals, then terminal stability is improved, but ion exchange groups react with fluorine causing difficulty in maintaining ion exchange capacity and durability
Solution Approach 1:
The patent performs preliminary stabilization of polymer terminals with fluorine gas before introducing ion exchange groups through reaction with compound (a). By stabilizing the terminals first, the subsequent introduction of ion exchange groups occurs on a stable backbone, preventing degradation of ion exchange capacity while maintaining terminal stability.
Solution Approach 2:
The patent maintains continuous protection of ion exchange groups by performing terminal stabilization before ion exchange group introduction, and by using compound (a) that selectively reacts with polymer chains without degrading the ion exchange groups. This continuous protective approach ensures ion exchange capacity is maintained throughout the synthesis process.
4Strength
If cross-linking is performed to improve membrane stability, then mechanical strength is improved, but solubility decreases making it difficult to prepare solutions for coating methods
Solution Approach 1:
The patent applies partial cross-linking by controlling the amount and reactivity of compound (a) introduced into the polymer. This partial action provides sufficient mechanical stability for membrane applications while maintaining enough solubility to allow solution preparation and coating methods. The cross-linking is optimized to achieve the minimum necessary stability without excessive cross-linking that would eliminate solubility.
5Reliability
If existing methods are used to produce ionic polymer membranes with multiple ion exchange groups, then ion exchange capacity is achieved, but the synthesis process becomes complex and durability decreases due to impurities
Solution Approach 1:
The patent merges multiple synthesis steps into a streamlined sequence: fluorinated polymer synthesis followed by reaction with compound (a) that simultaneously introduces multiple ion exchange groups and stabilizes the structure. This merging of operations reduces the number of separate synthesis steps, minimizes impurity formation, and simplifies the overall process while maintaining high ion exchange capacity.
Solution Approach 2:
The patent uses compound (a) as an intermediary reagent that facilitates the introduction of multiple ion exchange groups in a single controlled reaction step. This intermediary approach replaces complex multi-step functionalization sequences, reduces impurity formation, and simplifies the synthesis process while achieving high ion exchange capacity with improved durability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method results in an ionic polymer membrane with high ion exchange capacity and low water uptake, improving durability and economic efficiency, and enabling the production of electrolyte membranes, catalyst layers, and membrane/electrode assemblies for polymer electrolyte fuel cells.
Implementation Method 1
a step of reacting the polymer (ii) with a compound represented by formula (a) to convert the group represented by formula (2) in the polymer (ii) to a group represented by formula (3)
Implementation Method 2
thermal treatments to prevent cross-linking and achieve high ion exchange capacity and low water uptake
Implementation Method 3
a step of converting a —SO2F group in a polymer to a pendant group with multiple ion exchange groups
Data Source
AI summary
To provide a simple method whereby an ionic polymer membrane having a high ion exchange capacity and a low water uptake can be produced by converting a —SO2F group in a polymer to a pendant group having multiple ion exchange groups, while preventing a cross-linking reaction.At the time of obtaining an ionic polymer membrane by converting —SO2F (group (1)) in a polymer sequentially to —SO2NZ1Z2 (group (2)), —SO2N−(Mα+)SO2(CF2)2SO2F (group (3)), —SO2N−(H+)SO2(CF2)2SO2F (group (4)) and —SO2N−(Mβ+)SO2(CF2)2SO3−Mβ+ (group (5)), the polymer is formed into a polymer membrane in the state of any one of the groups (1) to (4), and the polymer membrane is thermally treated in the state of group (4). Here, Z1 and Z2 are hydrogen atoms, etc., Mα+ is a monovalent cation, and Mβ+ is a hydrogen ion or a monovalent cation.