How dense are cylindrical brushes grafted from a multifunctional macroinitiator?

A series of cylindrical brushes with poly(methyl methacrylate) (PMMA) and poly(n-butyl acrylate) (PBA) side chains of different lengths was studied to understand the grafting density of brush molecules prepared by the ‘grafting from’ approach. Molecules with PMMA side chains were prepared by grafting MMA from a multifunctional macroinitiator, poly(2-(2-bromoisobutyryloxy)ethyl methacrylate). Molecules with PBA side chains were prepared with poly(2-(2-bromopropionyloxy)ethyl methacrylate) as a macroinitiator. Analysis of the detached side chains showed an incomplete initiation process resulting in longer side chains than expected for complete initiation. Limited initiation (40-80%) was also observed for short PMMA chains using a low molar mass initiator ethyl 2-bromoisobutyrate with CuCl catalyst systems. The lower initiation efficiency was confirmed via visualization of individual molecules by atomic force microscopy. The larger distance between adsorbed brush molecules was consistent with <50% initiation efficiency.