Diazonium Salt-Derived 4-(Dimethylamino)phenyl Groups as Hydrogen Donors in Surface-Confined Radical Photopolymerization for Bioactive Poly(2-hydroxyethyl methacrylate) Grafts

Abstract

In this paper we describe a novel methodology for grafting polymers via radical photopolymerization initiated on gold surfaces by aryl layers from diazonium salt precursors. The parent 4-(dimethylamino)benzenediazonium salt was electroreduced on a gold surface to provide 4-(dimethylamino)phenyl (DMA) hydrogen donor layers; free benzophenone in solution was used as a photosensitizer to strip hydrogen from the grafted DMA. This system permitted efficient surface initiation of photopolymerization of 2-hydroxyethyl methacrylate. The resulting poly(2-hydroxyethyl methacrylate) (PHEMA) grafts were found to be very adherent to the surface as they resist total failure after being soaked in the well-known paint stripper methyl ethyl ketone. The PHEMA grafts were reacted with 1,1'-carbonyldiimidazole to yield carbamate groups that are able to react readily with amino groups from proteins. The final surface consisted of protein-functionalized PHEMA grafts where bovine serum albumin (BSA) protein is specifically linked to the grafts by covalent bonds. We used X-ray photoelectron spectroscopy to monitor the chemical changes at the gold surface all along the process from the neat gold to the end-protein-functionalized polymer grafts: the PHEMA graft thickness ranged from 7 to 27 nm, and the activation by 1,1'-carbonyldiimidazole reached 37% of the OH groups, which was sufficient for 90% surface coverage of the grafts by BSA. This work conclusively provides a new approach for bridging reactive and functional polymers to surfaces via aryl diazonium salts in a simple, fast, and efficient approach of importance in biomedical and other applications.

Diazonium salts for surface-confined visible light radical photopolymerization

“…In previous publications we have employed grafted hydrogen donors from diazonium salts for conducting radical polymerization using benzophenone as photosensitizer capable of abstracting hydrogen from the aryl layers . In this work, we electro reduced the structurally designed diazonium salt in order to attach dimethylaminophenyl (DMA) groups as hydrogen donor species.…”

“…Through accurate combinations of substrates, diazonium salts, polymerization methods and functional monomers, it became possible to design efficient and robust systems for removal of heavy metals, bioactive surfaces, electrochemical and optical sensors, and supercapacitors . In these systems, diazonium salts have a central role as they bridge the support to the reactive and functional polymers.…”

Synthesis of clickable hydrogels and linear polymers by type II photoinitiation

“…Free radical photopolymerization is based on the photochemical generation of initiating species through two main processes, namely cleavage (type I) or hydrogen abstraction (type II) reactions. In type II systems, initiating radicals are generated by bimolecular interactions of compounds whose triplet excited states readily react with hydrogen donors . Many thioxanthone and camphorquinone based photoinitiators have been developed and successfully used in various applications …”

Efficient photoinduced In situ preparation of clay/poly(glycidyl methacrylate) nanocomposites using hydrogen‐donor silane

“…Thus, homopolymer formation is minimized and higher grafting efficiencies are achieved. For example, surfaces functionalized with hydrogen‐donating sites were prepared using dimethylamino‐functionalized thiols or diazonium salts in view of designing reactive and functional coatings, clay/polymer nanocomposites, or bioactive hybrid platforms by radical graft‐photopolymerization.…”