Solution behavior of temperature-responsive molecular brushes prepared by ATRP

Molecular brushes, with side chains consisting of two copolymers: 2-(dimethylamino)ethyl methacrylate with methyl methacrylate, and NN-dimethylacrylamide with butyl acrylate were prepared by grafting-from via atom transfer radical polymerization (ATRP). Poly(2-(2-bromoisobutyryloxy) ethyl methacrylate) and poly(2(2 -bromopropionyloxy) ethyl methacrylate) were used as macroinitiators. Dynamic light scattering (DLS) studies were performed for aqueous solutions of molecular brushes below and above the lower critical solution temperature (LCST), and an unusual concentration-dependent LCST was observed. Due to the compact structure of molecular brushes, intramolecular collapse can occur when the average distance between molecules is much larger than the hydrodynamic dimensions of the individual macromolecules. However, if the concentration of the solution of molecular brushes is increased to the level in which the separation distance is comparable with the brush hydrodynamic dimensions, intermolecular aggregation occurs, as typically observed for solutions of linear polymers.