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

Abstract

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.

Green synthesis of polymer materials via enzyme- initiated RAFT polymerization

“…Smith et al reported the synthesis of polymer brushes via RAFT of poly(2-vinylpyridine) (P2VP) on an inimer-coated silica surface, which exhibits high chemical stability against many organic solvents even at high temperatures. 108 The synthetic pathway chosen yields high grafting densities and allows the end-group functionalization for the generation of low surface energy domains after thermal annealing by thiol–ene ‘click’ chemistry. An alternative field of application for polymer brushes synthesized by “grafting-from” RAFT is shown by Choi et al 109 Polymer brushes of di(ethylene glycol) methylether methacrylate (DEGMA) were synthesized on titanium-coated glass substrates, which illustrated excellent anti-fouling properties and can be further tuned to allow cell adhesion after coupling of arginyl glycyl aspartic acid (RGD).…”

Porous Morphology of High Grafting Density Mixed Polyelectrolyte Brushes Grown from a Y-Inimer Coating

“…Most commonly, self-assembled monolayers (SAMs) have been used to grow homopolymer and mixed brushes by grafting-from methods . To overcome some of the limitations of SAMs, such as limited stability to various reagents, substrate-dependent anchoring chemistry, degrafting of swollen brushes, and nonhomogeneous distribution of initiators, , and to achieve high grafting density A/B mixed brushes, we have developed ultrathin, cross-linkable inimer-containing coatings for brush growth using controlled radical polymerization methods. ,− These coatings contain either two types of inimers that can orthogonally grow A and B brushes, respectively, or a Y-shaped inimer that bears two distinct initiators attached at a single junction point for high grafting density mixed A/B brush growth by sequential surface-initiated atom transfer radical polymerization (SI-ATRP) and nitroxide-mediated polymerization (SI-NMP). , The Y-inimer coating is especially useful for the synthesis of mixed PE brushes as it ensures intimate contact between oppositely charged brushes and an equal grafting ratio.…”