Application Of Silicon Quantum Dots In "Living"/Controlled Radical Polymerization

Photo-induced"living"/controlled radical polymerization combines the advantages of photochemistry,such as environmentally friendly,mild reaction conditions,and excellent time and space contrability,with"living"/controlled radical polymerization,which can synthesize polymers with precise molecular weights and well-defined structures.It provides a new method for preparing functional materials which has a wide range of applications in the fields of biomaterials,block and graft copolymer preparation,nanocomposites,and surface modification.At present,many types of photocatalysts had been developed,such as metal complexes,organic non-metals,metal oxides,quantum dots and so on.However,traditional metal-based catalysts were easy to remain and had high toxicity,and most organic catalysts were difficult to synthesize.Therefore,the development of metal-free,non-toxic and harmless photocatalysts has become a research hotspot.Silicon quantum dots(SiQDs),as a kind of semiconductor nanocrystals,are rich in content,simple to prepare,and have low cytotoxicity and good biocompatibility,which makes SiQDs a very competitive low-cost catalyst.In addition,surface-initiated living radical polymerization technology had become an important means for preparing functional surfaces and synthesizing composite materials with specific functions.However,in most polymerization systems,apart from the catalysts,an additional linking agent was required to combined initiators with substrates.Due to the functionality of the amino groups on the surface of SiQDs,SiQDs can play dual roles for photocatalysts and linking agents between polymers and substrates,thereby providing a simple method for surface-initiated polymerization.In this paper,amino-terminated SiQDs were used as photocatalysts to perform photo-induced electron or energy transfer reversible addition-fragmentation chain transfer(PET-RAFT)polymerization and photo-induced atom transfer radical polymerization(ATRP)under visible light.And then considering the functionality of the amino groups on the surface of SiQDs,it was used as the linking agent between the RAFT reagents and the substrates and the photocatalyst for surface-initiated PET-RAFT polymerization.(1)A series of PET-RAFT polymerizations were carried out under visible light irradiation by using amino-terminated SiQDs synthesized by hydrothermal method as photocatalysts,and the influences of different solvents,light resources and monomers on the polymerization were explored.The experimental results showed that the polymerizations exhibited good controllability,and polymer with precise molecular weight and narrow molecular weight distribution was obtained.In addition,the introduction of electron donors could increase the polymerization rate.(2)A series of light-induced ATRP experiments were carried out under visible light using the amino-terminated SiQDs prepared above as the photocatalysts.And we studied the impact of different solvents and monomers on the polymerization by changing the experimental conditions.The results showed that the ATRP catalyzed by SiQDs exhibited good"living"characteristics,and the resulting polymer had well-defined structure and narrow molecular weight distribution.It was proved that SiQDs could be used as general catalysts for PET-RAFT polymerization and light-induced ATRP,and the versatility of SiQDs in different monomers and solvents had also been proved.(3)Considering the functionality of the amino groups on the surface of SiQDs,it provided a possible facile way for the surface-initiated PET-RAFT polymerization.SiQDs can play as a bridge between substrates and carboxyl group ended chain transfer agents(CTAs)and catalysts for PET-RAFT polymerization as well.The results showed that the polymer brushed were successfully grafted on the surface of silicon wafer and Si O₂particles.Kinetic studies had shown that the molecular weight of the surface grafted polymers could be controlled by controlling the photopolymerization time,so that the regulation of the thickness of the polymer shell layer on the Si O₂ surface realized.