Terraced and Smooth Gradient Polymer Brushes via a Polymer Single-Crystal Assisted Grafting-To Method.

Gradient polymer brushes provide a spatial gradient change in molecular characteristics of the brush, and such a change can be utilized to study structure-property relationships in a combinatorial fashion. In this study, a bottom-up method was used to synthesize gradient polymer brushes with a predesigned and precisely controlled grafting density gradient and brush pattern. A polymer single-crystal assisted grafting-to (PSCAGT) method was employed where end-functionalized polymers were grown into two-dimensional polymer single crystals. The latter were chemically coupled to a solid substrate to form well-defined polymer brushes. To tune the grafting density, end-dissimilar polymers were used to co-crystallize into one single crystal. Programmed single-crystal growth was introduced to synthesize brushes with two different gradient architectures, that is, terraced and smooth gradient with pyramid patterns. This work demonstrates that the PSCAGT method offers a unique means to tune polymer brush nanostructure.