Chain End-Functionalized Dense Polymer Brushes from an Inimer Coating by SI-RAFT

Polymer brushes with controllable grafting density are grown on an inimer coating bearing Reversible Addition-Fragmentation Chain Transfer polymerization (RAFT) chain transfer agents (CTAs). The inimer coating is cross-linked on the substrate to provide an initiator layer that is stable during exposure to organic solvents at high temperatures. Surface-initiated RAFT is conducted to grow poly(2-vinylpyridine) (P2VP) brushes on the coating at grafting densities approaching the theoretical limits. This methodology allows facile end-group functionalization using an efficient thiol-ene click chemistry. Chain ends were functionalized with low surface energy groups to modulate the location of the untethered chain ends by thermal annealing. At lower grafting densities, the low surface energy groups segregate to the surface upon annealing. This effect is less pronounced at higher grafting densities. Detailed characterization of the brushes at varying grafting densities using X-ray photoelectron spectroscopy (XPS) is presented. In tandem with experiments, Monte Carlo simulations examine the effect of the chain-end group size and selectivity on the conformation of the polymer brush, providing numerical evidence of laterally non-uniform distributions of functional groups at different locations in the brush. Simulations further predict the existence of morphologies with an interlayer formed by spherical micelles rich in functional end groups, demonstrating the possibility of end-group functionalization for synthetic modulation of both brush conformation and chain-end location.