Synthesis And Properties Of Polymers With Multiple Topologies

As one of the basic parameters of polymer structures,chains' topologies play an important role in the properties of block copolymers such as self-assembly, thermo-properties,and mechanical properties.However,it is still less studied concerning the detailed relationship between the polymer topologies and properties, since it is difficult for the preparation of polymers with some special topologies such as ring polymers and multiblock copolymers.In this dissertation,a series of block copolymers with particular topologies involving linear and cyclic diblock copolymers, multiblock copolymers,and novel star polymers,were prepared in the combination of widely-noted controlling radical polymerizations(CRP),supramolecular self-assembly,and click chemistry.The properties of the obtained polymers including the self-assembly and thermo-properties were also researched.The dissertation includes the following four parts:1.As for the synthesis and aggregation behavior of linear and cyclic diblock copolymers,three works are concerned.First,we prepared thermo-responsive double hydrophilic block copolymers(DHBCs)of N,N-dimethylacrylamide (DMA)and N-Vinyl Caprolactam(VCL)by the use of MADIX(Macromolecular Design via Interchange of Xanthanes).The aqueous solution of the obtained polymer,PDMA-b-PVCL,showed similar phase transition behavior with those more common DHBCs containing PNIPAM block,while it is more expectable for this new polymer to be used in biomedical fields since PVCL is more biocompatible than the PNIPAM.Second,double thermo-responsive block copolymer of 4-vinylpyridine(4VP)and NIPAM,P4VP-b-PNIPAM,was prepared via the consecutive atom transfer radical polymerization(ATRP).When the temperature of the aqueous solution of P4VP-b-PNIPAM with 8-aminonaphthalene-1,3,6-trisulfonic acid disodium salt(ANTS)(pH 1.5)was low,the polymers self-assembled into vesicles due the complex between the protonated P4VP block and SO₃^-;with the temperature increasing,the complex was destroyed and the block copolymer dissolved molecularly;while when the temperature was even higher,micelles was formed due to the lower critical solution temperature(LCST)behavior of PNIPAM block.Namely,the nano-aggregates of P4VP-b-PNIPAM can be easily transformed from vesicles to micelles upon heating.Thirdly,we prepared cyclic poly[2-(dimethylamino)ethyl methacrylate]- b-poly-[2-(diethylamino)ethyl methacrylate] (cyclic-PDMAEMA-b-PDEAEMA)via the intramolecular ring-closure reaction of linear-PDMAEMA- b-PDEAEMA,in selective solvents at relatively high concentrations.Owning to self-assembly of the linear precursor,the reactive end functionalities were spatial organized and interchain coupling was effectively prevented.On the other hand,intrachain ring-closure reactions can proceed unhindered for unimers at a concentration of critical micellar concentration(CMC) which was often very low.Thus,cyclic block copolymers can be prepared with high efficiency at relatively high concentrations.The obtained cyclic pH-responsive DHBC showed different aggregation behavior compared with its linear precursor.2.Using a synthesized polytrithiocarbonate,we prepared multiblock DHBCs via RAFT polymerizations.First,a series of multiblock copolymers of DMA and NIPAM with different sequence length were prepared,and the micellation behavior at low concentration and gelation behavior at relative high concentration were further researched compared with corresponding diblock and ABA triblock copolymers,respectively.It was found that when the PNIPAM block was short and PDMA block was long,unimolecular micelle and gelation behavior occured at low and high concentrations,respectively.While multimolecular micelles and phase separation occurred for the polymers with long PNIPAM sequence and short PDMA sequence.The gel from multiblock copolymers showed higher strength and lower critical gelation concentrations(CGCs)compared with that from ABA triblock copolymers.Furthermore,it was found that addition of inorganic salts can effectively facilitate the gelation behavior,such as elevating the gel strength and decreasing the CGC valuses.On the basis of the work concerning gelation behavior of multiblock copolymers,multiblock copolymer of 4-vinylpyridine and NIPAM,m-P(NIPAM-co-DMA)-b-P4VP,was further synthesized to prepare multi thermo-responsive physical gel.When sodium 2,6-naphthalene disulfonate was added into the aqueous solutions of m-P(NIPAM- co-DMA)-b-P4VP(pH 1.5),physical gels can be obtained both at tow and high temperatures while free-flowing solution was obtained at the middle temperatures in the range of body temperature,i.e.,Gel-Sol-Gel transition was achieved for the first time upon heating the aqueous solution.3.On the basis of the works concerning the aggregation behavior of block copolymers in selective solvents mentioned above,we are further devoted to fixation of the nano-structures from the self-assembly of block copolymers.First, we synthesized a new monomer,1-(3'-aminopropyl)-4-acrylamido-1,2,3-triazole hydrochloride(APAT),via click chemistry and its block copolymer with NIPAM, PNIPAM-b-PAPAT,via RAFT polymerization.On the basis of the reaction between amine groups of the PAPAT block and glutaric dialdehyde,core cross-linked and shell cross-linked micelles with inverted structures were prepared at 25℃and 50℃,respectively.Furthermore,the shell or core of the crosslinked micelles can be modified with gold nanoparticles due to the metal coordination and stabilization properties of the triazole groups along the PAPAT block.In the second work,we prepared ABA block copolymer ofγ-methacryloxypropyl- trimethoxysilane(MPS)and ethylene oxide (PMPS-b-PEOob-PMPS)with different PMPS block lengths via RAFT polymerizations.In aqueous medium,this block copolymer self-assembled into nano-aggregaetes whose morphologies were largely influenced by the block length and the initial organic common solvent,furthermore,the structure of the aggregated can be self-fixed at the same time due to hydrolysis and cross-linking of the PMPS block in water.4.In the last section,we prepared two novel structured star polymers in the combination of ATRP and click chemistry.First,core crosslinked star polystyrene (PS)with dialkynyl groups on the surface per arm,was pre-synthesized by polymerizing divinylbenzene(DVB)employing a dialkynyl-containing ATRP macroinitiator.Then the surface of the star polymer was intramolecularly crosslinked using octa(3-azidopropyl)polyhedral oligomeric silsesquioxane, POSS-(N₃)₈,as the inorganic multifunctional crosslinker at high dilution concentration via click chemistry,forming a novel POSS/polymer hybrid nanostructure.Thermogravimetric analysis shows that after surface crosslinking, the thermostability of the core crosslinked PS can be remarkably improved.In the second work,we synthesized of a novel polymer with quatrefoil-shaped topology. Star-linear-polystyrene(starolinear-PS)with～8 linear arms was pre-synthesized from atom transfer radical polymerization(ATRP)employing an eight-functional initiator.Then the objective polymer,star-cyclic-PS,was prepared via intramolecular arm-arm coupling of the star-linear-PS precursor via click reaction at high dilution concentration.Differential scanning calorimetry thermograms (DSC)characterization showed that star-cyclic-PS possessed a little higher glass transition temperature(T_g)than that of the star linear precursor.