Effect of catalyst deactivation on polymerization of electrolytes by surface-confined atom transfer radical polymerization in aqueous solutions

We have investigated the cause of catalyst deactivation observed during surface-confined atom-transfer radical polymerization of acidic monomers. Surface-tethered polyelectrolyte layers of poly(itaconic acid) and poly(methacrylic acid) were grown from self-assembled initiator monolayers of 2-bromoisobutyryl bromide terminated thiol molecules. This polymerization initiator molecule and a copper-based organometallic catalyst allowed tethered polyelectrolyte chains to be grown directly via radical polymerization at room temperature in aqueous solutions. Structural and surface properties of the layers were characterized using phase-modulated ellipsometry and external-reflection Fourier transform infrared spectroscopy. Catalyst deactivation due to generation of a coordination complex between the deprotonated acid monomers and copper catalyst during the polymerization process appears to be an important cause of chain growth cessation. Surface-initiated polymerizations performed after aging of the catalyst-containing deprotonated monomer solution revealed inhibition of polymer growth with increasing aging times. This suggests that catalyst is consumed over time by complexation with carboxylate groups of the monomer and dissociation and disproportionation in water.