Study On Synthesis, Characterization And Properties Of Amphiphilic Star Polymers With Polycaprolactones As Hydrophobic Blocks

Amphiphilic star block copolymers and amphiphilic star heteroarm polymers possessing the properties of both amphiphilic linear block copolymers and branched polymers are able to self-assemble into polymeric micelles in water. Compared to the conventional micelles from amphiphilic linear block copolymers, the micelles formed from amphiphilic star polymers have higher stability and higher loading capacity, which makes them very attractive in diverse fields of medicine and biology. In this thesis, we synthesized and characterized five series of amphiphilic star polymers with polycaprolactones as hydrophobic segments, and investigated their properties. The main results obtained in this thesis are as follows.The star-shaped poly(ε-caprolactone)-b-poly(2-(dimethylamino) ethyl methacryl-ate) (HPs-Star-PCL-b-PDMAEMA) was synthesized by ring-opening polymerization (ROP) and reversible addition-fragmentation chain transfer (RAFT) polymerization. The resultant polymer was characterized by 1H-NMR and GPC. Furthermore, the micellar properties of HPs-Star-PCL-b-PDMAEMA in water were studied at various temperatures and pH values by means of dynamic light scattering (DLS). The results indicated that the hydrodynamic diameters of micelles decreased with increasing pH and temperature of aqueous solutions. The release behaviors of model drug aspirin from the star polymer indicated that the rate of drug release increased with the decrease of pH value and temperature of aqueous solutions.The amphiphilic star block copolymers HPs-Star-PCL-b-P(NIPAAm-co-DMAEMA) with a hyperbranched polyester (HPs) core, a hydrophobic poly(ε-caprolactone) (PCL) inner shell and a hydrophilic copolymer of NIPAAm and DMAEMA (P(NIPAAm-co-DMAEMA)) outer shell were synthesized by ROP and atom transfer radical polymerization (ATRP). The star block copolymers were characterized using'H-NMR spectrum and GPC analysis. The crystallization behavior of star block copolymer was investigated by DSC, XRD, and polarized optical microscope (POM). The results indicated that the branched structure and the presence of PNIPAAm and PDMAEMA segments reduced the capacity of the PCL segments to crystallize. The micellar properties of the star block copolymer were studied by DLS, fluorescence spectroscopy and AFM. The results showed that unimolecular micelles and aggregated multimolecular micelles coexisted in the star block copolymer aqueous solution. The lower critical solution temperature (LCST) depended on both the NIPAAm/DMAEMA feed molar ratio and the pH value of water. In pH 3 buffer solution, when the feed molar ratio of NIPAAm to DMAEMA is more than 8/1, LCST increased from 34℃to 54℃with decreasing NIPAAm/DMAEMA feed molar ratio. However, when the feed molar ratio of NIPAAm to DMAEMA is less than or equal to 8/1, no phase transiton could be observed up to 60℃. In pH 9 buffer solution, the increase of DMAEMA content in the star copolymer led to the gradual increase of LCST from 35℃to 40℃. The release behaviors of model drug indomethacin from the star polymer micelles indicated that the rate of drug release increased with the increase of pH value and temperature.The heterofunctional macroinitiator (OH)4-PAMAM-(Br)4 was synthesized by sequential Michael addition reaction of acryloyloxyethyl 2-bromoisobutyrate and 2-hydroxyethyl acrylate with amine-terminated PAMAM. The heteroarm star polymer (PCL)4-PAMAM-(PDMAEMA)4 was obtained via ROP and ATRP, and was characterized using 1H-NMR and GPC. Heteroarm star polymer could self-assemble into spherical micelles in aqueous solution, which were characterized by TEM and DLS. In addition, the increase of temperature resulted in a noticeable decrease in hydrodynamic diameter. Silver nanoparticles were prepared by in situ synthetic method utilizing PDMAEMA as both reductant and stabilizer. The average size of the silver nanoparticles was about 7 nm. The hybrid micelles had an obvious surface plasmon resonance absorption band, and a red-shifting plasmon peak as environmental temperature increaseed. Finally, a model was proposed to explain the formation of silver nanoparticles.The star block copolymer HPs-Star-PCL-b-PtBMA with a hyperbranched polyester (HPs) core, poly (ε-caprolactone) (PCL) and poly (tert-butyl methacrylate) (PtBMA) segments was synthesized by ROP and ATRP. Subsequently, the PtiBMA segments were converted into poly (methacrylic acid) (PMAA) segments by hydrolysis with trifuoroacetic acid. The star block copolymers were characterized by 1H-NMR and GPC. Interpolymer complexes were prepared from HPs-Star-PCL-b-PMAA and poly (N-vinylpyrrolidone) (PVP) in dimethyl formamide (DMF). At 3/7 of the mass ratio of PVP to HPs-Star-PCL-b-PMAA, the blue-opalescent solution was formed. At 5/5 and 7/3 of the mass ratio of PVP to HPs-Star-PCL-b-PMAA, precipitates were formed immediately on mixing DMF solutions of HPs-Star-PCL-b-PMAA and PVP. The hydrodynamic diameters of complexes increased with increasing PVP dosage.The hydrogen bonding interactions of the complexes were investigated using FT-IR and DSC. It was revealed that there was very strong hydrogen bonding interactions between the carboxyl groups of PMAA segments of HPs-Star-PCL-b-PMAA and the carbonyl groups of PVP. The self-assembly behavior of complexes was examined by TEM and DLS. It was observed that spherical micelles and vesicles were formed at the low mass ratio of PVP to HPs-Star-PCL-b-PMAA. With increasing PVP content in the complexes, the particles of interpolymer complexes coiled up and aggregated to large dimension, even precipitated. Finally, a model was proposed to explain the aggregation process of the HPs-Star-PCL-b-PMAA/PVP complexes. The polyelectrolyte complexes were prepared from HPs-Star-PCL-b-PMAA and poly(allylamine hydrochloride) (PAH), which were characterized by UV-Vis, DLS, TEM andξ-potential. When the mass ratio of PAH to HPs-Star-PCL-b-PMAA was less than or equal to 2/8, water-soluble complexes had core-shell-corona structure, with a core formed by the hyperbranched polyester and PCL, a shell assembled from the coupled oppositely charged polyelectrolyte fragments, and a corona built up from the fragments of PMAA segments not involved in the interpolyelectrolyte. At 3/7 of the mass ratio of PAH to HPs-Star-PCL-b-PMAA, multimicellar aggregates were formed due to the bridging action of PAH among polyelectrolyte complexes particles. When the mass ratio of PAH to HPs-Star-PCL-b-PMAA was more than or equal to 4/6, the precipitate was formed as aggregated solid structure. Finally, a model was proposed to explain the formation of HPs-Star-PCL-b-PMAA/PAH complex. The amphiphilic star block polyelectrolyte HPs-Star-PCL-b-QPDMAEMA with a hyperbranched polyester (HPs) core, a hydrophobic PCL inner shell and a hydrophilic quaternized poly (2-(dimethylamino) ethyl methacrylate) (QPDMAEMA) outer shell was synthesized by ROP and ATRP. The star block copolymers were characterized by 1H-NMR and GPC. HPs-Star-PCL-b-PMAA was assembled alternately with HPs-Star-PCL-b-QPDMAEMA at different pH conditions to form pH-responsive multilayer films characterized using QCM and AFM. The film thickness increased linearly with increasing bilayer numbers for each pH value of the HPs-Star-PCL-b-PMAA solution. The film thickness and roughness increased with decreasing pH value of HPs-Star-PCL-b-PMAA solution. For the multilayer films buildup at the HPs-Star-PCL-b-PMAA dipping solution of pH 5, the surface roughness and grain size of the film increased distinctly as the number of deposited bilayers increased. For the film prepared from the HPs-Star-PCL-b-PMAA solution of pH 9. the diameters of the granules were approximately 50-100nm, and the surface roughness and grain size of the film showed no significant difference during assembly. The multilayer films were treated by immersion into pH 2 and pH 11 solutions after assembly. AFM measurements showed that all the multilayer films were stable in pH 2 aqueous solution. The multilayer films deposited at HPs-Star-PCL-b-PMAA solutions of pH 5 and pH 7 were unstable in pH 11 aqueous solution. The effect of dipping time, polyelectrolyte concentration and ionic strength on the formation of multilayer films by sequential adsorption of HPs-Star-PCL-b-QPDMAEMA and poly (sodium-p-styrenesulfonate) (PSS) was investigated by means of UV-Vis absorption spectroscopy, QCM and AFM. The results demonstrated that the multilayer films grew linearly with increasing layer number. The growth rate first increased as dipping time increased, then saturated beyond the dipping time of approximately 15min. The amount of polyelectrolyte deposited per bilayer rapidly increased with increasing polyelectrolyte concentration up to 0.5 mg/mL, while the solution concentration above 0.5 mg/mL had no appreciable effect on the adsorbed amount. With increasing ionic strength, the polyelectrolyte chains underwent a transition from an extended to a coiled conformation, which led to an increase in the thickness and surface roughness of multilayer film. For the film prepared from a salt concentration of 0.5 mol/L NaCl, small pores with typical diameters of 14-20 nm and apparent depths of 6-10 nm were observed. Finally, a model was proposed to explain the LbL assembly of HPs-Star-PCL-b-QPDMAEMA and PSS in aqueous solutions with various salt concentrations.