A photocleavable stabilizer for the preparation of PHEMA nanogels by dispersion polymerization in supercritical carbon dioxide

Abstract

A new photo-sensitive diblock copolymer composed of a hydrophilic sequence of poly(ethylene oxide) (PEO) linked to a CO₂-philic sequence of poly(1H,1H,2H,2H-heptadecafluorodecyl acrylate) (PFDA) by a light sensitive o-nitrobenzyl group was successfully synthesized by RAFT polymerization and used as a stabilizer for the free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) dispersion in α,α,α-trifluorotoluene and supercritical carbon dioxide (scCO₂). Thanks to this fluorinated stabilizer, well-defined particles of PHEMA down to 350 nm diameter were produced in scCO₂. Advantageously, the photocleavable group at the block junction of the stabilizer could be cleaved by exposing the particles to UV light so that the fluorinated block could be extracted in TFT or scCO₂. As supported by X-ray photoelectron spectroscopy (XPS) analysis, up to 80% of the fluorinated block of the stabilizer can be removed, leading to efficient swelling and dispersion of the resulting PHEMA nanogels in water.