Synthesis Of Star-shaped Water-soluble Polymers By Single-electron Transfer Living Radical Polymerization

Star polymers with compact three-dimensional core-shell structure are a special kind of branched macro-molecules.They are widely used in biomedical and industrial fields.Presently,star polymers with different sizes and functions can be prepared via controlled radical polymerization.In this work,?-bromoisobutyryl bromide(BIBB)was used to modify functional groups of macromolecules glycerol ethoxylate(Gly)and hyperbranched polyethylenimine(HPEI),a series of novel initiators were synthesized as star-shaped core,and they were used to prepare aqueous stimuli responsive star-shaped polymers.The supramolecular hydrogel was constructed through combining the star-shaped poly(dimethylaminoethyl methacrylate)and partially hydrolyzed polyacrylamide.The structure-property relationships between polymer structure and performance were analyzed.The main research contents and results were listed below:(1)The homopolymerization of AM and copolymerization of AM?Na AMPS and NVP were carried out at 0?in aqueous solution,using Gly-Br₃as iniator,full in situ disproportionation of CuBr/Me₆TREN to Cu(0)powder and Cu^?Br₂/Me₆TREN as catalyst system.Multifunctional initiator Gly-Br₃was synthesized by acylation of poly(ethylene glycol ether)with 2-bromoisobutyryl bromide.The polymers prepared via SET-LRP were characterized by¹H NMR,FT-IR and GPC.The effects of temperature,initiator types and molar ratio of CuBr/Me₆TREN on the homopolymerization of AM were investigated.The results show that the appropriate molar ratio of CuBr to Me₆TREN is 1.5:1.Water-soluble initiator is suitable to initiate the SET-LRP of AM at low temperature,while oil-soluble initiator is opposite.The effects of reaction time,temperature,initiator concentration,CuBr dosage and molar ratio of CuBr/Me₆TREN on the copolymerization were also investigated.The results show that the liner increment of ln([M]₀/[M])with time was maintained throughout polymerization,which could indicate a first order propagation rate with respect to both radicals and monomer concentration.Further discussion revealed that the lower temperature is more conducive to the living/“controlled”polymerization in this experiment.With the increasing of CuBr/Me₆TREN(mola ratio)and initiator concentration,the monomer conversion and molecular weight both increase first and then decrease.The copolymer has excellent properties of temperature resistance and salt resistance.It is expected to be used as targeted flooding polymer in high-temperature and high-salinity oil reservoir.(2)A novel star-shaped copolymer containing nano-SiO₂by SET-LRP in aqueous solution was reported.The results confirmed that the nano-SiO₂functional monomer was successfully combined in the SET-LRP.The optimum polymerization conditions were established through orthogonal experiments as a ratio of[AM]:[AANa]:[I]:[CuBr]:[Me₆TREN]of 1687.5:562.5:1.0:2.3:1.5 at a total concentration of[AM]+[AANa]of 4.5mol/L.The appropriate concentration of nano-SiO₂functional monomer(NSFM)was 0.5wt%with respect to AM+AANa.The rheology of the star-shaped copolymer exhibited a shear thickening property when the shear rate exceeded a critical value(100 s^-1).It was found that AM/DMAEMA/NSFM exhibited better salt and temperature tolerances.(3)In order to efficiently synthesis the thermal responsive star-shaped polyacrylamides,we investigated the copolymerization of acrylamide with AM-based macromonomer(MPAD)by single-electron transfer living radical polymerization(SET-LRP).Copolymerizations using Gly-Br₃as initiator were catalyzed by full in situ disproportionation of CuBr/Me₆TREN to Cu(0)powder and CuBr₂and performed in H₂O at 0?.The polymerization proceeded smoothly and the time dependence of ln([M]₀/[M])was linear,which could indicate the copolymerizations were the living polymerizations.The effects of monomor mass ratio,initiator and catalytic system on the controllability of copolymerization of AM and MPAD were studied.With the increase of MPAD dosage,the chain growth rate constant k_p^appdecreased gradually.With the increase of initiator concentration and the molar ratio of CuBr/Me₆TREN,the conversion and the molecular weight of the copolymer increased first and then decreased.The responsive behaviors of the water-soluble star-shaped copolymers have been studied by turbidity measurements and Dynamic light scattering.The lower critical solution temperature(LCST)of random copolymer can be tunable by changing the feed ratio of MPAD in the random copolymer.And star-shaped P(AM-co-MPAD)has excellent viscosity retention at high temperature.(4)A series of macroinitiators derived from HPEI were used to initiate the SET-LRP of DMAEMA at 0?in aqueous solution.The polymers prepared were characterized by ¹H NMR,FT-IR and GPC.The effects of DMAEMA/H₂O(v/v)on polymerization were studied and the optimum condition was given.The response behavior of star-shaped PDMAEMA with different amounts of arms was studied by turbidimetry.The results showed that the process is a well-controlled living radical polymerization.With the increase of the arms,the LCSTs of star PDMAEMA decreased,the thermo sensitive property of the copolymer can be magnified by the increasing arms.The supramolecular hydrogel was constructed by blending star-shaped PDMAEMA with HPAM.The effects of PDMAEMA structure on the viscosity of HPAM aqueous solution were investigated.The results show that the star-shaped PDMAEMA can improve the viscosity of HPAM aqueous solution;with the increasing arms of PDMAEMA,the viscosifying ability is improved;compared with HPAM,the PDMAEMA/HPAM supramolecular hydrogel solution system has excellent heat resistance,salt resistance and shear resistance.(5)The synthesis of a well-defined dual-responsive double-hydrophilic star-block copolymer by SET-LRP in aqueous solution is reported.Conditions for iterative block formation have been optimized for an N-isopropylacrylamide three-armed star-shaped polymer,which was prepared with DP=120-360 with full conversion in<30 min with polydispersity index((?))<1.18.A well-defined block polymer containing N-isopropylacrylamide,dimethylaminoethyl methacrylate,and N-vinylpyrrolidone has been prepared in high purity.The(?)after each chain extension was below 1.20.The responsive behaviors of the block-star copolymer have been studied.The phase transition temperature of the star-block copolymer increased with decreasing pH.At pH 3.0,the copolymer displayed weak thermo-responsive behavior.At higher pH(8.6 and10.0),the star-block copolymer showed a strong thermal response and formed spherical micelles and vesicles.