Application Of Upconversion Nanorods In Near-infrared Light Photo-induced Controlled Radical Polymerization

Controlled radical polymerization（CRP）is a major revolution in polymer chemistry,enabling the synthesis of a wide range of functional polymers with precise sequences,molecular weights,low dispersion and well-defined structures,which has greatly contributed to the further development of the polymer discipline.Over the past decade,photoinduced controlled/living radical polymerization has developed into an excellent strategy for achieving spatial and temporal control of polymerization under mild reaction conditions.The most commonly used ones are photoinduced electron transfer-reversible addition-fragmentation chain transfer polymerization（PET-RAFT）and photo-atom transfer radical polymerization（Photo-ATRP）.Photocatalysts play a crucial role in photoinduced CRP,but most current photocatalysts can only perform polymerization reactions under the radiation of short-wavelength light,which limits their applications in polymerization due to poor penetration and side reactions such as initiation of polymer decomposition.In recent years,near-infrared（NIR）photoinduced polymerization has been widely used in polymer synthesis for its high penetration,low safety risk,no self-initiation and polymer degradation.In particular,rare earth element-doped upconversion materials with stable luminescence color and intensity,low toxicity,and resistance to photobleaching can stably convert long-wave NIR light to short-wave UV or visible light,thus activating the photocatalyst as an internal light source to initiate polymerization,which is currently the most common NIR photoinduced polymerization strategy.However,the quantum yield of the upconversion material is low and the fluorescence intensity needs to be enhanced as much as possible.Optimizing the spectral match and energy transfer distance between the upconversion material and the catalyst is the main strategy to enhance the polymerization efficiency.Based on this,the main researches of this thesis are as follows:（1）A series of UCMs with tunable dimension,size,and fluorescence color were prepared and applied to NIR PET-RAFT polymerization.By comparing the fluorescence intensity of different UCMs and the spectral match with the catalyst,the green fluorescent UCNR withβcrystalline had the best degree of spectral overlap and fluorescence intensity,and thus the efficiency of assisted catalytic NIR PET-RAFT polymerization was relatively high,while the polymerization also showed good activity and controllability.The NIR PET-RAFT polymerization reactions under different conditions of monomer,polymerization degree,and oxygen tolerance were verified,indicating the excellent versatility of the system.Finally,the penetrating nature of the NIR photo polymerization was demonstrated using pig skin and chicken skin as barriers.（2）A novel photocatalyst UCNR@Si O₂@EY was prepared by covalently coupling the optimized green fluorescent UCNR with the organocatalyst eosin Y,then applied to catalyze aqueous-phase NIR PET-RAFT polymerization.The grafting of EY on the UCNR surface greatly shortens the energy transfer distance and improved the catalytic efficiency of the polymerization reaction.The encapsulated Si O₂ not only dispersed the catalyst into aqueous,but also prevented the occurrence of fluorescence quenching.The EY grafted to the Si O₂ surface underwent red-shifting,leading to better spectral matching and photobleaching resistance of the catalyst.In combination with ultrafiltration centrifuge tubes,efficient separation of the catalyst from the polymerization product is achieved,avoiding contamination and degradation of the final polymerization product.（3）A novel catalyst,UCNR@Si O₂@CDs,was prepared by coupling UCNR@Si O₂ with carbon quantum dots（CDs）via simple positive and negative electrical interactions,which can catalyze aqueous-phase NIR Photo-ATRP polymerization.The utilization of CDs simplifies the synthesis steps and avoids the inherent photodegradation properties of organocatalysts.The effects of different CDs loadings and different Cu Br₂ contents on the polymerization of NIR Photo-ATRP were investigated,and the controllability of polymerization increased significantly with the increase of Cu Br₂ content,however,the polymerization rate decreased.The addition of Na Br improved the controllability of the polymerization reaction at high DP and effectively avoided the contamination of the final polymerization product by excess Cu Br₂ despite the reduced polymerization rate.The vacancy trap EDTA-2Na can significantly improve the catalytic efficiency of the catalyst,and the mechanism of UCNR@Si O₂@CDs-catalyzed polymerization of NIR Photo-ATRP in the presence of oxygen is discussed.Finally,hydrogels with end-group initiation activity were prepared,which can be used not only for the preparation of multifunctional block hydrogels,but also for the deep repair of hydrogels.（4）In situ NIR PET-RAFT polymerization was used for the surface functionalization modification of UCNR.Various shell-polymers were prepared using different monomers.The molecular weight of polymers brushs on the UCNR@PMMA with different reaction times was investigated in relation to the polymer shell layer size,graft density,and fluorescence intensity.After that,different methods were used to prepare UCNR@Au,and the effects of different solvents,different reductant agent types,and different precursor concentrations on the Au NP of UCNR surface were discussed.While the surface plasma energy transfer pathway of UCNR@Au and the effect of surface plasma effect on the fluorescence spectrum of UCNR@Au were also investigated.