Acrylamide-Based Copolymers Bearing Photoreleasable Thiols for Subsequent Thiol-Ene Functionalization

A new set of monomers is presented in order to incorporate thiols into radical polymers using a protecting chemistry/photocleavage route. The (co)polymerization kinetics of an o-nitrobenzyl thioether-containing acrylamide derivative are reported. The presence of the o-nitrobenzyl moiety is found to strongly affect the polymerization. Nevertheless, water-soluble copolymers with N,N-dimethylacrylamide (DMAAm) as a comonomer are obtained either by free radical polymerization (10 000 <= M-n <= 17 500 g mol(-1); 1.5 <= PDI <= 1.8) or by reversible addition-fragmentation transfer (RAFT)-mediated controlled/living radical polymerization (2000 <= M-n <= 5700 g mol(-1); 1.1 <= PDI <= 1.2). Deprotection under UV light (lambda = 366 nm) at ambient temperature is followed by UV/vis monitoring of the protecting group release, which proceeds to completion between 40 min and 2 h within the studied range of concentration as demonstrated by H-1 NMR spectroscopy. Thiol-maleimide addition is subsequently carried out and found to proceed with a nearly quantitative yield (ca. 90%) as measured by H-1 NMR. Different block copolymers (9400 <= M-n <= 16 500 g mol(-1); 1.3 <= PDI <= 1.4) with a PDMAAm water-soluble block, a polystyrene hydrophobic block, or a poly(N-isopropylacrylamide) thermosensitive block as the first segment and possessing the photoreleasable thiol moieties in the second block are subsequently synthesized by RAFT-mediated polymerization. We finally demonstrate the orthogonal sequential deprotection and reaction with benzyl maleimide of two different thiol species originating from the thiocarbonylthio functionality and the o-nitrobenzyl protected lateral groups, respectively.