A novel heterogeneous catalytic system consisting of Eosin Y conjugated to silica nanoparticle (EY-SNP) is explored in this work to promote visible light photoinduced electron/energy transfer–reversible addition–fragmentation chain transfer (PET-RAFT) polymerization. In contrast to unconjugated Eosin Y (EY) that has been extensively studied and employed in free radical and controlled/“living” radical polymerization, EY-SNP was found to be tolerant to photodegradation during the polymerization. In addition, ultralow concentration of EY-SNP (less than 10 ppm) was found to efficiently catalyze polymerization of hydrophobic and hydrophilic monomers to reach high monomer conversions with narrow molecular weight distributions in a range of different solvents, including water, dimethyl sulfoxide, and N-methyl-2-pyrrolidone. Finally, the EY-SNP was also recovered via centrifugation and was reused to perform multiple cycles of polymerization.

In this communication, we investigate the photoinduced electron/energy transfer−reversible addition− fragmentation chain transfer (PET-RAFT) polymerization of 2-(methylthio)ethyl methacrylate (MTEMA) using 5,10,15,20tetraphenylporphine zinc (ZnTPP) as a photocatalyst under visible red light (λ max = 635 nm). Interestingly, the polymerization kinetics were not affected by the presence of air as near identical polymerization kinetics were observed for nondeoxygenated and deoxygenated systems, which is attributed to the singlet oxygen quenching ability of MTEMA. In both cases, well-defined polymers were obtained with good control over the molecular weight and molecular weight distribution (MWD). Furthermore, we have demonstrated that MTEMA can undergo the polymerization-induced self-assembly (PISA) process from a poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) macromolecular chain transfer agent (macro-CTA) to yield well-defined polymeric nanoparticles of various morphologies. These nanoparticles were rapidly disassembled after exposure to visible light due to the formation of singlet oxygen by the encapsulated ZnTPP and subsequent rapid oxidation of the thioether group.

We report a facile benchtop process for the synthesis of cross-linked polymeric nanoparticles by exploiting wavelength-selective photochemistry to perform orthogonal photoinduced polymerization-induced self-assembly (Photo-PISA) and photo-crosslinking processes. We first established that the water-soluble photocatalyst, zinc meso-tetra­(N-methyl-4-pyridyl) porphine tetrachloride (ZnTMPyP) could activate the aqueous PET-RAFT dispersion polymerization of hydroxypropyl methacrylate (HPMA). This photo-PISA process could be conducted under low energy red light (λmax = 595 nm, 10.2 mW/cm2) and without deoxygenation due to the action of the singlet oxygen quencher, biotin (vitamin B7), which allowed for the synthesis of a range of nanoparticle morphologies (spheres, worms, and vesicles) directly in 96-well plates. To perform wavelength selective nanoparticle cross-linking, we added the photoresponsive monomer, 7-[4-(trifluoromethyl)­coumarin] methacrylamide (TCMAm) as a comonomer without inhibiting the evolution of the nanoparticle morphology. Importantly, under red light, exclusive activation of the photo-PISA process occurs, with no evidence of TCMAm dimerization under these conditions. Subsequent switching to a UV source (λmax = 365 nm, 10.2 mW/cm2) resulted in rapid cross-linking of the polymer chains, allowing for retention of the nanoparticle morphology in organic solvents. This facile synthesis of cross-linked spheres, worms, and vesicles demonstrates the utility of orthogonal light-mediated chemistry for performing decoupled wavelength selective chemical processes.