Research On The Synthesis And Application Of Amphiphilic Block Copolymers Via RAFT Polymerization

With the development of controlled/"living" polymerization inrecent years, it’s convenient to synthesize the amphiphilic blockcopolymers with controlled molecular weight and narrow molecularweight distribution. Among the available controlled/“living”polymerization techniques, the reversible addition-fragmentation chaintransfer （RAFT） polymerization has received much attention due to itscompatibility with a wide range of monomers, functional groups andconvenient experimental conditions. Amphiphilic block copolymers canself-assemble to form micelles in water. Amphiphilic block copolymersas stabilizers in emulsion polymerization are expected to overcomedisadvantages caused by low molecular weight surfactants. Latex wasstabilized by steric stabilization or electrosteric stabilization. So theresearch on amphiphilic block copolymers used as emulsifier inemulsion polymerization caused more and more attention. Wesynthesized and characterized two series of amphiphilic blockcopolymers with poly（acrylic acid） as hydrophilic segments in thisthesis. Their properties and applications in the emulsion polymerizationwere investigated. The main results obtained are as follows.Poly（acrylic acid） was synthesized via RAFT polymerization byusing2-{[（dodecylsulfanyl）carbonothioyl]sulfanyl}succinic acid（DCTSS） as chain transfer agent. The structure of the polymer wascharacterized by FT-IR,1H-NMR and GPC. Kinetic exhibited first-orderpolymerization and the monomer conversion increased linearly withtime, exhibiting the living polymerization characteristics. Themolecular weight distribution of the final polymerization products wasless than1.37. The molecular weight and molecular weight distributionhas little effect by changing the molar ratio of V501to CTA. The molecular weight increased linearly with increasing the molar ratio ofAA to CTA.Amphiphilic block copolymer poly（acrylic acid）-b-polystyrene（PAA-b-PS） was obtained by chain extending reaction of PAA via RAFTpolymerization. The structure of the polymer was characterized byFT-IR,1H-NMR and GPC. A series of PAA-b-PS with molecular weightdistribution from1.07to1.23were obtained by changing the molarratios of V501to PAA-RAFT and St to PAA-RAFT, which indicated thatthe polymerization was controllable. Results of the properties study ofPAA-b-PS in aqueous solution showed that the optimal emulsifyingproperty achieved when the molar ratio of V501to CTA was0.2, molarratio of AA to CTA was20, molar ratio of V501to PAA-RAFT was0.1,and molar ratio of St to PAA-RAFT was20. The emulsifying propertyof PAA-b-PS was much better than that of low molecular surfactants,such as SDS, SDBS and MS-1, and with low foamability and foamstability. The CMC of PAA-b-PS in aqueous solution was estimated tobe2.940×10^-4g/mL, which was lower than that of SDBS(CMC=3.240×10^-3g/mL). However, the surface tension could only reduce to39.89mN·m-1. The ability of reducing surface tension was weaker thanthat of SDBS. With increasing the amount of alkali, the surface tensiondramatically increased to a maximum and then decreased. Then thePAA-b-PS with optimal emulsifying property was used in emulsionpolymerization of styrene-acrylate. The effects of some parameters onthe emulsion and properties of its film were investigated. The emulsionwas characterized by FT-IR,1H-NMR, DLS and TEM. Evaluating theobtained results, the optimal synthesis conditions were the NaHCO3mass fraction of0.55wt%, the ammonium persulfate mass fraction of0.8wt%, the PAA-b-PS mass fraction of4wt%, the AA to CTA molarratio of20, the St to PAA-RAFT molar ratio of20, the BA to St massratio of60to40. The latex particles were uniform spheres with thediameter about90nm and narrow distribution observed by TEM, whichwas consistent with the results measured by DLS.Amphiphilic block copolymer poly（acrylic acid-b-hexafluorobutyl acrylate）（PAA-b-PHFBA） was obtained by chain extending reaction ofPAA via RAFT polymerization. The structure of the polymer wascharacterized by FT-IR,1H-NMR and GPC. A series of PAA-b-PHFBAwith molecular weight distribution from1.16to1.47were obtained bychanging the molar ratios of V501to PAA-RAFT and HFBA toPAA-RAFT, which indicated that the polymerization was controllable.Results of the properties study of PAA-b-PHFBA in aqueous solutionshowed that the optimal emulsifying property achieved when the molarratio of AA to CTA was30, molar ratio of V501to CTA was0.15, molarratio of HFBA to PAA-RAFT was15, and molar ratio of V501toPAA-RAFT was0.1. The emulsifying property of PAA-b-PHFBA wasmuch better than that of low molecular surfactants, such as SDS, SDBSand MS-1, and with low foamability and foam stability. The CMC ofPAA-b-PHFBA in aqueous solution was estimated to be1.35×10^-4g/mL,which was much lower than that of SDBS(CMC=3.240×10^-3g/mL).Meanwhile, the surface tension could reduce to39.89mN·m-1, more orless with SDBS. With increasing the amount of alkali, the surfacetension dramatically increased to a maximum and then decreased. Thenthe PAA-b-PHFBA with optimal emulsifying property was used in theemulsion polymerization of fluorinated polyacrylate. The effects ofsome parameters on the emulsion and properties of its film wereinvestigated. Evaluating the obtained results, the optimal synthesisconditions were the ammonium persulfate mass fraction of1.2wt%, thePAA-b-PHFBA mass fraction of4wt%, the HFBA mass fraction of10wt%, the BA to MMA mass ratio of7to3. The contact angle wouldreach a maximum of96.8°when the amount of HFBA was10wt%. TGAanalysis showed that the initial decomposition temperature and thermalstability increased with increasing the amount of HFBA. The filmformed from the fluorinated polyacrylate emulsion with PAA-b-PHFBAas emulsifier showed higher thermal stability and hydrophobocity thanthat of DNS-86as emulsifier. The TEM and DLS results indicated thatthe latex particles presented uniform spherical core-shell particles about80nm in diameter and a narrow particle size distribution. XPS and CA analysis showed that the signal intensity of the fluorine in the film-airinterface was higher than that in the film-glass interface, suggesting thefluorine preferentially concentrated at the film-air interface during filmformation process. Finally, schematic representation of the formation ofcore-shell fluorinated polyacrylate particles with poly（acrylicacid-b-hexafluorobutyl acrylate） trithiocarbonate as emulsifier wasproposed.