A Dynamic Duo: Pairing Click Chemistry and Postpolymerization Modification To Design Complex Surfaces

Abstract

Advances in key 21st century technologies such as biosensors, biomedical implants, and organic light-emitting diodes rely heavily on our ability to imagine, design, and understand spatially complex interfaces. Polymer-based thin films provide many advantages in this regard, but the direct synthesis of polymers with incompatible functional groups is extremely difficult. Using postpolymerization modification in conjunction with click chemistry can circumvent this limitation and result in multicomponent surfaces that are otherwise unattainable. The two methods used to form polymer thin films include physisorption and chemisorption. Physisorbed polymers suffer from instability because of the weak intermolecular forces between the film and the substrate, which can lead to dewetting, delamination, desorption, or displacement. Covalent immobilization of polymers to surfaces through either a "grafting to" or "grafting from" approach provides thin films that are more robust and less prone to degradation. The grafting to technique consists of adsorbing a polymer containing at least one reactive group along the backbone to form a covalent bond with a complementary surface functionality. Grafting from involves polymerization directly from the surface, in which the polymer chains deviate from their native conformation in solution and stretch away from the surface because of the high density of chains. Postpolymerization modification (PPM) is a strategy used by our groups over the past several years to immobilize two or more different chemical functionalities onto substrates that contain covalently grafted polymer films. PPM exploits monomers with reactive pendant groups that are stable under the polymerization conditions but are readily modified via covalent attachment of the desired functionality. "Click-like" reactions are the most common type of reactions used for PPM because they are orthogonal, high-yielding, and rapid. Some of these reactions include thiol-based additions, activated ester coupling, azide-alkyne cycloadditions, some Diels-Alder reactions, and non-aldol carbonyl chemistry such as oxime, hydrazone, and amide formation. In this Account, we highlight our research combining PPM and click chemistry to generate complexity in polymer thin films. For the purpose of this Account, we define a complex coating as a polymer film grafted to a planar surface that acts as a template for the patterning of two or more discrete chemical functionalities using PPM. After a brief introduction to grafting, the rest of the review is arranged in terms of the sequence in which PPM is performed. First, we describe sequential functionalization using iterations of the same click-type reaction. Next, we discuss the use of two or more different click-like reactions performed consecutively, and we conclude with examples of self-sorting reactions involving orthogonal chemistries used for one-pot surface patterning.

Buckling Instabilities in Polymer Brush Surfaces via Postpolymerization Modification

“…34 The extended chain conformation of brushes has specific implications for the PPM process, where the high osmotic pressure and reduced chain conformational entropy disfavor the penetration of reactive modifiers into the brush. 35, 36 Thus, the penetration depth and the through-thickness compositional homogeneity of the brush resulting from the PPM process are ultimately dependent on i) the reaction conditions (solvent quality, reaction efficiency, and reaction time), ii) the tethered brush parameters (grafting density and thickness), and iii) the physical properties of the reactive modifier (molecular mass and steric bulk).…”

“Shine & Click” Photo‐Induced Interfacial Unmasking of Strained Alkynes on Small Water‐Soluble Gold Nanoparticles

“…The Popik group reported a cyclopropenone‐masked dibenzocyclooctyne (DIBO) that undergoes clean decarbonylation under ultraviolet A (UV‐A) irradiation to afford DIBO . They have also demonstrated the application of these cyclooctyne precursors in the surface functionalization of patterned polymer brush films . However, derivatization of AuNPs or Au surfaces with cyclopropenone‐masked DIBO moieties has never been reported.…”

Cyclopropenone-caged Sondheimer diyne (dibenzo[a,e]cyclooctadiyne): a photoactivatable linchpin for efficient SPAAC crosslinking

“…3 These quintessential “click-chemistries” have found numerous applications in molecular biology, 3b–c,4 drug development, 5 biotechnology, 6 and materials science. 3a,7 The SPAAC ligation is better suited for applications in living systems as it avoids the use of cytotoxic copper catalysts. 8 In addition, terminal acetylenes were found to inhibit cysteine proteases by forming thioethers with the catalytically active thiol.…”