Rapid Synthesis of Functional Polymer Brushes by Surface-Initiated Atom Transfer Radical Polymerization of an Acidic Monomer

Abstract

The combination of a highly reactive monomer, 2-(methacryloyloxy)ethyl succinate (MES), and active catalyst systems, e.g., Cu(I) complexed with 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA), allows rapid formation of poly(carboxylic acid) brushes by atom transfer radical polymerization (ATRP) from a surface. ATRP from initiators immobilized on Au-coated Si wafers yields films with an ellipsometric thickness of 120 nm in less than 15 min. To the best of our knowledge, this is the first example of direct ATRP of protonated acidic monomers that is capable of yielding such thick films, and MES polymerizes much more rapidly than methacrylic acid both in solution and on a surface. The MES films are attractive for a number of applications, including immobilization of proteins. Assuming that a lysozyme monolayer has a thickness of 2 nm, a 55 nm poly(MES) brush binds ∼70 monolayers of lysozyme via ion-exchange interactions. Additionally, when derivatized with nitrilotriacetate−Cu2+ complexes, poly(MES) films bind ∼34 monolayers of BSA through metal-ion affinity interactions (assuming a BSA monolayer thickness of 4 nm). These binding capacities are similar to those of poly(acrylic acid) brushes prepared by polymerization of tert-butyl acrylate and subsequent hydrolysis, but the poly(MES) synthesis is a one-step, aqueous process.