Molecular Brushes with Spontaneous Gradient by Atom Transfer Radical Polymerization

Spontaneous gradient copolymers were synthesized by atom transfer radical polymerization (ATRP) of acrylates and methacrylates and were subsequently employed to prepare macroinitiators for the synthesis of molecular brushes. Simultaneous copolymerizations of methyl methacrylate (MMA) and 2-(trimethylsilyloxy)ethyl acrylate (HEA-TMS) with different monomer feed ratios were conducted, and the resulting poly(MMA- grad -HEA-TMS) copolymers were transformed to a macroinitiator, poly(MMA- grad -(2-(2-bromopropionyloxy)ethyl acrylate) (BPE)). Another monomer pair of 2-(trimethylsilyloxy)ethyl methacrylate (HEMA-TMS) and n -butyl acrylate ( n -BA) was also used for a simultaneous copolymerization for comparison between these two systems. Brushes were synthesized from these macroinitiators by the “grafting from” method with n -BA. The gradient composition of the backbone was formed spontaneously due to the difference in the reactivity ratios of the two monomers. The reactivity ratios were determined by nonlinear least-squares calculations for both monomer pairs from conversion data obtained by gas chromatography. AFM images confirmed the gradient shape of brushes by resolving two different ends of brushes: densely grafted heads and loosely grafted tails.