Near Infrared Light Induced Atom Transfer Radical Polymerization

Photo-induced ATRP is one of the active radical polymerization methods,which has the advantages of energy saving,mild,high efficiency and good temporal control of the polymerization,which is widely used in the design of polymer molecular structure and the synthesis of functional polymer materials.The core of ATRP is to establish balance between activation and deactivation in the process.Generally,the balance is established by introducing free radical initiator,metal catalyst or heating.In addition,it is another important way to activate chemical reaction by light irradiation,which has been widely studied because of its mild reaction conditions,fast polymerization rate and controllable time space ompared with other activation methods.However,most of the light sources of ATRP are UV light,which has poor penetration and its application in large-scale ATRP is limited.In addition,the UV light with high energy may be harmful in some organic and biological systems,and lead to side reactions,such as self initiated polymerization and polymer decomposition.These problems can be solved by using the near infrared light with low energy and long wavelength.With low Rayleigh scattering near-infrared light(NIR)is hardly absorbed by traditional photosensitive components.Therefore,it is not only beneficial for side reaction but improve the depth.However,the absorption wavelength of traditional photoinitiators or photosensitizers is concentrated in the near ultraviolet and visible region,which can not match with the NIR light(700 nm-2500 nm).Although the maximum absorption wavelength of cyanine is close to 800 nm,the synthesis route is complex and the storage stability is poor.Rare earth upconversion materials can absorb near-infrared light and produce ultraviolet/visible light.In order to improve the applicability of photo-ATRP,NIR induced upconversion particles(UCPs)in situ luminescence was used to realize ATRP radical polymerization,and the structure and properties of the polymer were further improved through the design and optimization of NIR-ATRP system.Under the irradiation of 980 nm near-infrared light,upconversion particles(UCPs)can convert NIR light into UV/Vis light.UCPs are used as internal light source,ethyl 2-bromoisobutyrate(EBi B)as initiator,copper bromide(CuBr₂)/N,N,N'',N''',-pentamethyldiethanolamine(PMDETA)as catalyst,the Cu(?)was reduced to Cu(?)by direct irradiation in the presence of excessive amine ligands,balance between active species and dormant species was achieved,and realizing photo induced ATRP in near infrared band.The polymerization process and mechanism were studied by adjusting the parameter.The results show that ATRP assisted by UCPs has the characteristics of living polymerization.The obtained polymer has controllable molecular weight and narrow molecular weight distribution,and the molecular weight increases linearly with the increase of monomer conversion.The feasibility of ATRP induced by near-infrared light assisted by UCPs was proved.In ATRP with copper halide as photocatalysis system,Cu(?)can be obtained by the electron transfer between Cu(?)and free radicals.Based on the first part,the photoinitiator matching with UCPs emission light is introduced in second part.UCPs are internal light source,EBi B as initiator,CuBr₂/N,N,N'',N''',-pentamethyldiethanolamine(PMDETA)as catalyst.The Cu(?)is reduced to Cu(?)by the free radicals generated by photolysis of photoinitiator,and SR&NI ATRP and reverse ATRP are realized in near infrared band.The proper photoinitiator was selected by the matching of the emission spectrum of UCPs and the absorption spectrum of photoinitiator and the polymerization result.The polymerization process and mechanism were studied by adjusting the parameter of polymerization.The results show that the UCPs assisted NIR induced SR&NI ATRP and reverse ATRP are suitable for monomers such as MMA,MA and St,and have the characteristics of living polymerization.The obtained polymer has controllable molecular weight and narrow molecular weight distribution,and the molecular weight increases linearly with the increase of monomer conversion.The free radicals produced by photoinitiators inevitably produced free radicals,which have a certain impact on the controllability of polymerization.It is necessary to introduce photocatalysts which can effectively reduce Cu(?)but couldn't initiate monomers.In the third part,decacarbonyl manganese[Mn₂(CO)₁₀]is introduced as a photocatalyst.The free radicals generated by this Mn₂(CO)₁₀ only reduce Cu(?)to generate Cu(?)in situ,but it couldn't react with the monomers in the system,which can retain the advantages of SR&NI ATRP and improve the controllability of the system.Using UCPs as internal light source,EBi B as initiator,CuBr₂/N,N,N'',N''',-pentamethyldiethanolamine(PMDETA)as catalyst,the Cu(?)was reduced to Cu(?)by the free radical produced by Mn₂(CO)₁₀ photolysis,and the electron transfer in NIR band was realized to generate activated ATRP.The polymerization process and mechanism were studied by adjusting the polymerization parameter.The results show that ATRP assisted by UCPs has the characteristics of living polymerization.The obtained polymer has controllable molecular weight and narrow molecular weight distribution,and the molecular weight increases linearly with the increase of monomer conversion.The NIR light used in this part has the longest wavelength and the lowest energy in the reported photo-induced ATRP.UCP assisted NIR-ATRPis a new method to realize living polymerization,which provides a new idea for the further development of NIR light induced ATRP.