Synthesis, Characterization And Study On The Self-assembly Of Amphiphilic Graft Copolymer Of Poly(Acrylic Acid) In Aqueous Solution

In water, the amphiphilic copolymer is energetically favorable to form micelles with its hydrophobic groups forming the core and the hydrophilic groups forming the outer shell through the self-assembly. Intensive interests on the self-assembly of amphiphilic copolymers in solution have been risen due to its potential applications in nano-materials, polymeric surfactants, biomedical substances and petrochemical technology. In order to study the effect of molecular structure on self-assembly, which can help people to reality for the controlling of micellar morphology and size, people expect to get the well-defined and controlled copolymers which is the main developing direction of modern synthetic high polymer Chemist.So far, much attention has been focused on the self assembly of amphiphilic block copolymer and most studies are performed in organic solvents. There are more reports about the synthesis of amphiphilic graft copolymer, but little descriptions were presented for the self-assembly of amphiphilic graft copolymers in aqueous solution in detail, the morphology of amphiphilic graft copolymers is till one of the dificults in polymer science. According to the state and trend , a well-defined amphiphilic graft copolymer of PAA as main chain were designed and synthesized by free radical copolymerization in our work, and the micellar formation of the amphiphilic graft copolymer in water were investigated in detail. This thesis consists of six parts.1. A surface-active macromonomer of C₈PhEO₁₀Ac was prepared with C₈PhEO₁₀ and acrylol chloride using toluene as solution in the presence of copper(I) chloride and triethylamine. The residue was further purified by column chromatography. The effects of acrylol chloride concentration, reaction temperature, reaction time and feeding order on the percentage of C₈PhEO₁₀ conversion have been discussed. The copolymer exhibited the expected structure as indicated by the results of detailed characterization with FT-IR, 1H-NMR, UV and fluorescence.2. A series of well-defined and water-soluble PAA-g-C₈PhEO₁₀Ac of PAA as main chain and C₈PhEO₁₀Ac as graft chains were synthesized by free radical copolymerization using K2S2O8 as initiator in water. The effects of monomer ratio,initiator concentration, reaction temperature, reaction time on the molecular weight and its distributions, the percentage of monomer conversion, grating and grating efficiency have been discussed. The copolymers obtained were characterized by FT-IR, 1H-NMR, UV, fluorescence, GPC, TG, DTA, the synthesis method of graft copolymer of PAA as main chain was feasible and successful.3. The CMC and correspondingγCMC values of the graft copolymer were obtained by surface tension measurements in aqueous solution. Influences of macromonomer and inorganic salt on CMC andγCMC have been investigated. Effects of the copolymer concentration and inorganic salts on the reduced viscosity of PAA-g-C₈PhEO₁₀Ac have been discussed. Dependence of absorption spectra on the micellar behavior of PAA-g-C₈PhEO₁₀Ac in aqueous solution on was studied. It was found that the CMC andγCMC decreased with the increase in the copolymer concentration. The presence of sodium chloride and magnesium chloride results in the lower CMC andγCMC. The graft copolymer is readily soluble in water and highly surface active at much lower concentration.4. The micellar behavior of PAA-g-C₈PhEO₁₀Ac in aqueous solution were studied by fluorescence technique using ANS, TNS and pyrene as probes. Influences of macromonomer, copolymer concentration, pH, NaCl and MgCl₂ on their fluorescence spectra were studied. The experimental results indicate that the fluorescence intensity increases with increasing concentration of AA-C₈PhEO₁₀Ac. these changes became sharper at CMC. The presence of NaCl and MgCl₂ results in the weaker polarity in micellar core and the fluorescence intensity of TICT of TNS and ANS sharply increases. The I1/I3 values of the pyrene decreases with the addition of inorganic salt; the microenvironmental polarity of the probes decreases with the rise in pH value in the range pH 6.2-8.0. The CMC of PAA-g-C₈PhEO₁₀Ac obtained by the fluorescence measurements is in a good agreement with those obtained by surface tension measurements.5. The micellization of PAA-g-C₈PhEO₁₀Ac in water have been monitored by fluorescent technique using EHS as a probe. Influences of the copolymer concentration, pH, NaCl and MgCl₂ on the fluorescence spectrum of EHS were investigated. The addition of PAA-g-C₈PhEO₁₀Ac resultes in sharply increased emission intensity with long wavelength for EHS with intramolecular hydrogen bonding and decreased emission intensity with short wavelength for EHS with intermolecular hydrogen bonding,the fluorescence intensity increases with increasing concentration of PAA-g-C₈PhEO₁₀Ac. Great changes in the long wavelength emission intensity and the peak position were made at CMC. The short wavelength emission intensity increased and the long wavelength emission intensity decreased from pH pH6.2 to pH8.0. The long wavelength emission intensity slightly decreases in the presence of NaCl. However, the effect of MgCl2 on the fluorescence of EHS is very different from that of NaCl. The long wavelength emission intensity of EHS begins to rapidly decrease with increasing concentration of AA-C₈PhEO₁₀Ac. Furthermore the bathochromic shift appears. The CMC of PAA-g-C₈PhEO₁₀Ac obtained by fluorescence measurements of EHS is in a good agreement with that obtained by surface tension measurements.6. The influences of copolymer concentration, pH, inorganic salts on surface topography and the shapes and sizes of PAA-g-C₈PhEO₁₀Ac micelles in water have been discussed using SEM and TEM. The results show that the micellar shapes and the sizes were dependent on copolymer concentration, pH and ionic strength. As the copolymer concentration increases, the micellar sizes became larger. The micellar shapes undergo spherical micelles, the spherical and columnar micelles and the spherical micelles again. The sizes of micelles increased with the addition of NaCl to water and decreased at high pH values. These findings are favorable for better understanding of the self-assembly of amphiphilic graft copolymer and were helpful for control of micellar shapes and sizes.