Synthesis of Poly(N,N-dimethylacrylamide) Brushes from Charged Polymeric Surfaces by Aqueous ATRP: Effect of Surface Initiator Concentration

Abstract

We have synthesized polystyrene shell latex (PSL) surfaces with different initiator concentrations by changing the feed ratio of styrene to 2-(methyl-2‘-chloropropionato)ethyl acrylate (HEA−Cl) in a series of shell-growth copolymerization reactions. Surfaces were characterized by conductometric titration of saponified and nonsaponified functionalized PSL to give the surface charge and initiator concentrations accessible to aqueous reagents and by 1H NMR methods. Poly(N,N-dimethylacrylamide) brushes were grafted from the functionalized surfaces by aqueous atom transfer radical polymerization and the dependence of molecular weight and chain density determined as a function of monomer concentration, ligand type, and surface initiator concentration by analyzing the chains cleaved from the PSL by saponification. Mn varies linearly with monomer concentration for most systems, and grafting density is roughly independent of monomer concentration except at the highest initiator concentration. Very high molecular weights were obtained at low initiator concentration, up to Mn ∼ 1.2 × 106 with Mw/Mn < 1.3; chain separations down to 1.1 nm and brush thicknesses to ∼800 nm were found. Grafting density varies as (initiator surface concentration)2.6. The surface charge density also varies among the latexes synthesized and seems to play a role in this strong dependence on surface initiator concentration, perhaps by partially immobilizing the positively charged catalyst complex.