Atom Transfer Radical Polymerization Of MMA And PEGA Catalyzed By Hematin

As one of the most widely used controlled/living radical polymerization techniques,atom transfer radical polymerization(ATRP)provides a new method for the synthesis of well-defined polymers with predetermined molecular weight and narrow molecular weight distributions and precisely controlled architecture.In the current ATRP catalytic system,copper-based catalysts are the most efficient for a broad range of monomers because of their high catalytic activity.However,the copper catalyst limits its application due to its high toxicity and unavoidable metal residues.Therefore,the development of "green" efficient ATRP catalytic system has always been a tireless pursuit of scientists.Consequently,enzyme,as environmentally friendly,non-toxic alternative to transition metal complexes,has been used to catalyze ATRP in recent years,but the control over the polymerization is limited,resulting in high molecular weight polymers with molecular weight distributions close to 1.5.This is due to their sensitivity to reaction conditions.Therefore,it is expected that analogs of enzymes can be developed to improve the degree of control over the polymerization and enhance the catalytic activity of the native enzyme on the basis of "green" polymerization.Based on the above research status,the ATRP of poly(ethylene glycol methacrylate)(PEGA)in aqueous and methyl methacrylate(MMA)in organic catalyzed by naturally occurring hematin which is used as precursor of ATRP catalyst,were studied systematically in order to extend green and efficient catalytic system range and to lay a theoretical foundation for further understanding the mechanism of enzyme catalyzed ATRP.First,the experimental method of ARGET ATRP catalyzed by heme was established by exploring the experimental conditions so that the polymerization can be medicated under low catalyst dosage.The effect of p H value on the activity of heme was investigated by cyclic voltammetry,which provided a guarantee for proper selection of reaction conditions and laid a theoretical foundation for the success of aqueous ATRP.Then the effect of p H value,initiator species,and concentration of hematin and ascorbic acid and target degree of polymerization(DP)on the polymerization kinetics was studied to master the law and characteristic of polymerization.Finally,UV/Vis was used to monitor the spectral changes of heme after the addition of initiator HEBIB in dimethyl sulfoxide model system with the initiator HEBIB,and the equilibrium constant of the reversible reaction between activation and deactivation in the model system was calculated according to Fisher's equation.The results show that the reaction kinetics of ARGET ATRP catalyzed by hematin is the first order reaction,the molecular weight increases with the increase of the conversion,the molecular weight distribution is less than 1.3,and obtained polymers can be used as macroinitiator to initiate polymerization of monomer.All this indicated that the polymerization is controlled/living radical polymerization and follows ATRP mechanism.Experimental results showed that the polymerization rate increases with the increase of reducing agent and decrease of catalyst.In DMSO model system,the equilibrium constant of reversible reaction between HEBi B and heme is 3.62 × 10-7,which is close to the equilibrium constant of CuIBr / HMTETA in the same solvent.The above studies have laid a theoretical support for the enzyme-catalyzed aqueous ATRP.In order to further extend the range of heme-catalyzed ATRP,the polymerization in organic was applied,since most of the vinyl monomers are oil-soluble,which can greatly extend the range of polymers that can be prepared by heme-catalyzed ATRP.We first studied the ATRP reaction with methyl methacrylate(MMA)as the reaction monomer and toluene / ethanol as the reaction solvent.The main research contents are as follows: the amount of Fe powder and tetrabutylammonium bromide on the kinetics of polymerization.The results showed that the ATRP of MMA can be implemented successfully in the presence of iron powder as reducing agent and tetrabutylammonium bromide.The polymerization reaction displayed first-order kinetics,the molecular weight increased with the conversion,and the molecular weight distribution was narrow.The polymerization reaction has the characteristic of controlled / living radical polymerization.The polymerization rate increases with the increase of tetrabutylammonium bromide in the system.Experiments results also show that species which play a catalytic role are heme and iron-based complex with bromine as ligand in the system,both of which synergistically mediate the atom transfer radical polymerization.Further,copolymers of methyl methacrylate and ethyl methacrylate are prepared in one pot by tandem ATRP catalyzed by heme and transesterification with aluminum isopropoxide as catalyst.