Research On Photo-induced Iron-Catalyzed ATRP Systems

Atom transfer radical polymerization(ATRP),as a powerful "living" radical polymerization method,has been attracting extensive attention from academia and industry since its discovery.In ATRP,transition metal salts are often used as catalysts for the system,such as copper,ruthenium,iron,and nickel salts.Compared with other transition metals,iron has many advantages,such as abundant reserves,low toxicity,and good biocompatibility,so iron-catalyzed ATRP has received particular attention these years.Light is an ideal green energy.Compared to thermochemistry,photochemistry has many advantages,such as low energy consumption,small environmental pollution,and safe operation.Therefore,it is significant to develop photo-induced iron-catalyzed ATRP.In addition,the metal residue in the polymer has always been an inherent defect of ATRP.It is of great practical value to remove and recycle the catalyst effectively in the polymer.The liquid/liquid biphasic system has the advantages of simple operation and high recycling utilization as a commonly used catalyst separation and recovery method.However,the liquid/liquid biphasic systems reported before,such as thermo-regulated phase transfer catalysis(TRPTC)and thermo-regulated phase separable catalysis(TPSC)all require the changing process from high temperature to low temperature.It is clear that these methods are not suitable for photo-induced systems conducted at room temperature.Fortunately,the polar/non-polar potential biphasic system can realize the change of homogeneous phase to two phase only by a simple post-treatment(such as adding a certain amount of water)without the change of temperature.Combining the content above,this dissertation focused on the construction of photo-induced iron-catalyzed ATRP system and the use of polar/non-polar two-phase system to further develop the catalyst separation and recovery system in photo-induced iron-catalyzed ATRP.The main research contents and conclusions are as follows:(1)Photo-Induced Iron-Catalyzed ATRP of Methyl Methacrylate Using 1,3-Dimethyl-2-Imidazolidinone as Both Solvent and Ligand.Iron salt is the most ideal transition metal catalyst for ATRP,while photo-induced ATRP has the advantages of mildness,high efficiency,low energy consumption,and small pollution.Combining the advantages of both,we constructed a photo-induced iron-catalyzed ATRP at room temperature successfully using FeBr2 as the catalyst,a "green" solvent 1,3-dimethyl-2-imidazolinone(DMI)as both solvent and ligand,ethyl 2-bromophenylacetate(EBPA)as the initiator and methyl methacrylate(MMA)as the model monomer without additional ligands and reducing agents.The polymer number-average molecular weight(Mn,GPC)increased linearly with monomer conversion and matched the predicted molecular weight.The molecular weight distribution was narrow(Mw/Mn<1.33).The polymerization system exhibited a relatively fast rate of polymerization(monomer conversion could reach 91.2%after 26 hours)and could be controlled well,even under a 1000 target degree of polymerization(Mw/Mn=1.28).Besides,the successful chain-extension experiments and the characterization(1H NMR and MALDI-TOF)of the polymer had proved the "living" end in the polymer.(2)Photo-induced Iron-Catalyzed Water-Induced Phase Separable Catalysis(WPSC)ICAR ATRP of Poly(ethylene glycol)Methyl Ether Methacrylate.In this chapter,a practical iron catalyst recycling system,photoinduced iron-catalyzed water-induced phase separable catalysis ATRP with initiators for continuous activator regeneration,at room temperature was developed for the first time.We constructed the ICAR ATRP using 5,10,15,20-tetraphenyl-21H,23H-porphine iron(?)chloride(Fe(?)-TPP)as the catalyst,tetrabutylammonium bromide(TBA-Br)as the ligand,and ethyl 2-bromophenylacetate(EBPA)as the ATRP initiator,2,4,6-trimethylbenzoyl-diphenyl phosphine oxide(TPO)as the photoinitiator and poly(ethylene glycol)methyl ether methacrylate as the model hydrophilic monomer in the homogeneous solvent system consisting of p-xylene and ethanol.After polymerization,a certain amount of water was added to induce the phase separation,so that the p-xylene(containing the catalyst)and the ethanol(containing the polymer phase and water)could be separated.For simplicity,we named this process water-induced phase separation catalysis(WPSC)ATRP.The system had good controllability and fast polymerization rate.The catalyst could still effectively control the polymerization after conducting recycle experiments for six times,and the metal residue in the polymer kept at a low level(<12 ppm).It was worth mentioning that all the materials used in this system are commercialized raw materials,there was no need to pre-synthesize the macro-ligand.