Reversible Addition-fragmentation Chain Transfer(RAFT) Polymerization Mediated By Low-energy Light Based On Inorganic Nanocrystals

Photo-induced controlled/�living�radical polymerization is a general method for preparing a variety of polymers with complicated and well-defined structures.It has wide applications in the synthesis of crosslinked polymers and nanoparticles.Among them,photo-induced reversible addition-fragmentation chain transfer?RAFT?polymerization technology has received widespread attention due to its advantages such as a wide range of applicable monomers,low temperature reaction and excellent ability to regulate polymerization.Since the light sources used for photo-induced RAFT polymerization are mostly high-energy light?e.g.,ultraviolet light?,it often brings some unavoidable side reactions.In addition,visible light limits their wide applications due to weak penetrating ability in most solutions.Therefore,it is necessary to develop RAFT polymerization systems in the low-energy light region?e.g.,near-infrared light?.Based on inorganic nanocrystals,the different RAFT polymerization systems were studied under near-infrared light and blue light.First,a simple and efficient ligand exchange method was used to modify the upconversion nanoparticles?UCNPs?.Then,the RAFT polymerization of various monomers was studied under the near-infrared light irradiation at 980 nm,and the RAFT polymerization was also successfully achieved when the vessel was shielded by biological tissues.Second,polymer brushes grew in situ on the surface of UCNPs by photo-RAFT polymerization under 980 nm light irradiation by anchoring chain transfer agents on the UCNPs surface.Finally,considering the recycling problem of nanocatalysts in the polymerization system,the?-Fe₂O₃ magnetic materials were introduced into the polymerization system.The polymerization processes of a series of monomers mediated by blue light were examined,and the magnetic nanoparticles could be recycled after polymerization.The main results are as follows:?1?UCNPs were prepared by solvothermal method,and the surface was modified by ligand-exchange method using NOBF₄.The RAFT polymerization of various monomers was performed under 980 nm irriadiation.In addition,the penetrability of near-infrared light was also investigated.The experimental results showed that NIR can mediate the RAFT process well,and all polymerization confirmed�living�characteristics.In the case of chicken skin or pig skin as a barrier,a higher conversion?>60%?can be achieved after 32 h irriadiation,which proved that NIR has excellent penetration performances for biological tissue materials.?2?Based on the UCNPs prepared above,a two-step ligand-exchange method was used to modify the UCNPs so the chain transfer agents were anchored on the surface of UCNPs.Then the core-shell nanostructures of UCNPs were prepared in situ under near-infrared irriadiation using photo-RAFT polymerization.The experimental results suggested that the thickness of the polymer shell layer could be adjusted by illumination time.The thickness of the polymer shell layer reached11.9�0.3 nm after 20 h irradiation.In addition,we also found that the fluorescence intensity of the system increased linearly with the molecular weight and monomer conversion of the free polymers.?3?Considering the recovery of nanocatalysts in the polymerization system,the?-Fe₂O₃ magnetic nanomaterials were introduced into the system to prepare?-Fe₂O₃@carbon dot nanocomposites,which were used as photocatalyst in the polymerization system.The RAFT polymerization of various monomers under blue light at room temperature was carried out.The experimental results indicated that the polymerization of all monomers showed�living�features,and the molecular weight distribution was narrow?M_w/M_n<1.35?,and it also displayed the dual regulation of polymerization by light and magnetism.More importantly,the introduction of magnetic nanomaterials into the polymerization system realized the recycling and reuse of nanomaterials successfully.