Methods and materials for removing metals in block copolymers

A method of forming a directed self assembly pattern comprising the steps of;

• a. coating a substrate with a solution with reduced metal ion contamination content, wherein the solution comprises a block copolymer where the block copolymer is derived from monomers which are arranged in blocks which are different compositionally, structurally or both and are capable of phase separating and forming domains, and further wherein the blocks have differing etch properties which can be used to remove one block while keeping the other block intact on the surface of the substrate, thus providing a pattern on the surface of the substrate and further where the solution with reduced metal ion contamination is produced by,
• i. treating the solution with a basic ion exchange to form a slurry;
• and,
• ii. filtering the slurry to remove the ion exchange resin;
• b. heating the substrate to form a directed self assembly polymer layer;
• and
• c. removing one block of the block copolymer and thereby forming a pattern.