Bioinspired Anchorable Thiol-Reactive Polymers: Synthesis and Applications Toward Surface Functionalization of Magnetic Nanoparticles

In this study, we report on the synthesis of novel thiol-reactive polymers containing a catechol moiety at their chain ends and demonstrate their application toward surface modification of magnetic nanoparticles. Poly(ethylene glycol) methyl ether acrylate (PEGMEA) based hydrophilic polymers incorporating maleimide group containing side-chains were synthesized using reversible addition fragmentation chain transfer (RAFT) polymerization. A novel furan-protected maleimide-containing acrylate monomer was synthesized and copolymerized with hydrophilic monomers in the presence of a catechol moiety containing chain transfer unit. Removal of the furan protecting group after polymerization yields thiol-reactive polymers possessing an intact catechol unit at their chain-end for anchoring onto various surfaces. Polymers with varying composition of the masked maleimide monomer were obtained with narrow molecular weight distributions as inferred from size exclusion chromatography. Obtained polymers were characterized using proton nuclear magnetic resonance ((HNMR)-H-1), infrared (IR) spectroscopy, and electrochemistry to establish their chemical composition. Oleic acid coated organo-dispersible magnetic nanoparticles were modified with the hydrophilic catechol terminated polymers to obtain water dispersible polymer-coated magnetic nanoparticles. The reactive maleimide units on the polymer-coated nanoparticles were utilized to conjugate thiol-containing hydrophobic dye using the nucleophilic Michael addition reaction to obtain water dispersible magnetic and fluorescent nanoparticles. Alternatively, it was demonstrated that radical thiol-ene reaction can also be utilized to functionalize nanoparticles coated with polymers where the maleimide group is in masked as a furan-cycloadduct. Efficient anchoring of the polymer onto nanoparticle surfaces and their subsequent functionalization was verified using various techniques such as infrared spectroscopy (IR), thermogravimetric analysis (TGA), and phase transfer studies, whereas the subsequent functionalization was evident from the organic to aqueous phase transfer of the hydrophobic fluorescent dye.