Polymer Brushes: Surface Initiated and Bottlebrush Self-Assembly

The term “polymer brush” may refer to chains closely bound to one another on a surface or chains bound to a central polymer backbone forming an architecture that has been described as a bottlebrush. Polymer brushes exhibit unique properties arising from the repulsive excluded volume interactions between adjacent polymer chains. These interactions can cause polymers chains that would normally exist as random coils to take on a highly extended conformation depending on the density of grafted chains. Surface bound polymer brushes have been used for a myriad of applications including colloidal stability, biocompatibility, and low-friction surfaces among others. Bottlebrushes are being studied for applications similar to those of linear block copolymers due to their ability to self-assemble. However, their chain conformation and self-assembly is dictated by architecture in a way that linear block copolymer assembly is not. We have investigated both surface bound brushes, grown by controlled radical surface-initiated polymerization, and bottlebrushes grown by anionic polymerization. We find that the distribution of polymers grown by surface-initiated polymerization contains a low molecular weight fraction that we argue is a result of terminations occurring early during polymerization. We have performed preliminary investigations into techniques for the reduction of brush polydispersity and have also used surface-initiated polymerization to enhance the dispersibility of nanofillers for composite materials. Our studies of amphiphilic bottlebrushes describe self-assembly trends and indicate a structural difference in the coronas of micelles formed by dense versus sparsely grafted bottlebrushes