Photo-Sensitive Raft-Agents For Advanced Microparticle Design

The current contribution describes the combination of an efficient reversible deactivation radical polymerization process (reversible addition fragmentation chain transfer (RAFT) polymerization) with a mild light-induced modular ligation technique. A novel RAFT-agent was synthesized which carries a photoactive group based on ortho-quinodimethane (photo-enol) chemistry. The novel photoreactive RAFT-agent controls the polymerization of a wide range of monomers such as styrene, N,N-dimethylacrylamide and a protected glycomonomer (2-(2',3',4',6'-tetra-O-acetyl-beta-D-mannosyloxy)ethyl acrylate) with dispersities between 1.07 and 1.17 (3500 g.mol(-1) <= M-n <= 10100 g.mol(-1)) and quantitative end-group functionalization. The photoenol group reacts with dieneophiles under mild irradiation (lambda(max) = 320 nm) at ambient conditions - so that the RAFT-group remains intact and without any catalyst to form block copolymers in a matter of minutes. Furthermore, the RAFT-polymers can be photografted onto porous polymeric (poly(glycidyl methacrylate)) microspheres, after a one-step prefunctionalization with maleimide moieties. The successful photografting is evidenced by scanning electron microscopy (SEM), elemental analysis (EA), X-ray photoelectron spectroscopy (XPS) and high resolution attenuated total reflectance (ATR) FT-IR microscopy, which leads to qualitative as Well as quantitative grafting data. The grafting densities obtained for polystyrene are close to 0.11 chains per nm(2) (M = 3900 g.mol(-l)) and for poly(N,N-dimethylacrylamide) close to 0.12 chains per nm(2) (M-n = 3500 g.mol(-1)). To highlight the additional benefit of employing a light-induced grafting reaction, Janus microspheres were prepared with poly(N,N-dimethylacrylamide) employing a Pickering emulsion approach and illustrated via ATR-FT-IR microscopy.