Process for preparing membranes and membrane structures from a sulfonated block copolymer fluid composition
First Claim
1. A process for preparing a membrane, comprising:
- (a) applying a fluid composition of sulfonated block copolymer, ester of residual carboxylic acid and non-halogenated aliphatic solvents onto the surface of a substrate, said fluid composition prepared by the steps of;
i. providing a precursor block copolymer having at least two end blocks A and at least one interior block B, wherein each A block is a polymer block resistant to sulfonation and each B block is a polymer block susceptible to sulfonation;
ii. reacting the precursor block polymer with a C2 to C8 acyl sulfate in a reaction mixture further comprising at least one non-halogenated aliphatic solvent to form a sulfonated block polymer, therein resulting in the formation of a solution of a sulfonated block copolymer and a residual carboxylic acid; and
iii. subsequently reacting the residual carboxylic acid contacted with a C1 to C4 alcohol or mixture thereof in a molar ratio of alcohol to residual carboxylic acid of at least 0.9;
1 to form the corresponding alkyl esters of the carboxylic acid and to reduce the residual level of the organic residual acid to less than 2.0 wt % based on the total weight of the solution, wherein the reaction mixture is free of any halogenated solvent,(b) spreading the fluid composition to form a uniform thickness layer on the substrate, and(c) allowing the solvent to evaporate from the fluid composition resulting in a solid membrane.
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Abstract
The present invention relates to an improved method for making sulfonated block copolymers and to methods for making membranes from such block copolymers. In particular, the present invention relates to an improved method for making sulfonated block copolymers having at least two polymer end blocks that are resistant to sulfonation and at least one polymer interior block that is susceptible to sulfonation where the sulfonation agent is C2 to C8 acyl sulfate. In the improved process the residual carboxylic acid formed from the C2 to C8 acyl sulfate is converted to C1 to C4 alkyl esters by contacting the residual carboxylic acid with at least a 0.9:1 molar ratio of a C1 to C4 alcohol to residual carboxylic acid, resulting in an improved sulfonated block copolymer solution. The present invention further relates to the use of such sulfonated block copolymer solutions to prepare various membranes and other articles.
137 Citations
11 Claims
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1. A process for preparing a membrane, comprising:
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(a) applying a fluid composition of sulfonated block copolymer, ester of residual carboxylic acid and non-halogenated aliphatic solvents onto the surface of a substrate, said fluid composition prepared by the steps of; i. providing a precursor block copolymer having at least two end blocks A and at least one interior block B, wherein each A block is a polymer block resistant to sulfonation and each B block is a polymer block susceptible to sulfonation; ii. reacting the precursor block polymer with a C2 to C8 acyl sulfate in a reaction mixture further comprising at least one non-halogenated aliphatic solvent to form a sulfonated block polymer, therein resulting in the formation of a solution of a sulfonated block copolymer and a residual carboxylic acid; and iii. subsequently reacting the residual carboxylic acid contacted with a C1 to C4 alcohol or mixture thereof in a molar ratio of alcohol to residual carboxylic acid of at least 0.9;
1 to form the corresponding alkyl esters of the carboxylic acid and to reduce the residual level of the organic residual acid to less than 2.0 wt % based on the total weight of the solution, wherein the reaction mixture is free of any halogenated solvent,(b) spreading the fluid composition to form a uniform thickness layer on the substrate, and (c) allowing the solvent to evaporate from the fluid composition resulting in a solid membrane. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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Specification