TEMPO Driven Mild and Modular Route to Functionalized Microparticles.

Abstract: The synthesis of crosslinked polymeric microspheres (3.8–15.0 µm) via (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) initiated thiol‐ene dispersion polymerization under ambient conditions is reported for the first time. The initiating ability of TEMPO for the thiol‐ene reaction is validated by electron paramagnetic resonance (EPR) and 1H nuclear magnetic resonance (NMR) spectroscopy on model reactions between 1‐octadecanethiol and two electron deficient enes, n‐butylacrylate and divinyl sulfone. Critically, the TEMPO resonance observed in the EPR spectra decreases with time when TEMPO is mixed with thiol and an electron deficient ene. The 1H NMR spectra demonstrate formation of up to 90% of thioether under ambient conditions. Based on these model reactions, a variety of crosslinked polymeric microspheres are synthesized with excellent morphological stability using poly(vinyl pyrrolidone) as surfactant. The ability of the microspheres for a second TEMPO initiated thiol‐ene reaction is demonstrated by the ligation of fluorescein‐5‐maleimide (an ene) to the microspheres' surface containing excess of thiol functionality and by ligation of cysteine (containing a thiol group) to the microspheres' surface containing an excess of ene functionality. The synthesized polymeric microspheres are characterized using scanning electron microscopy, differential scanning calorimetry, Fourier‐transform infrared spectroscopy, zeta potential, and X‐ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]