| Dendritic polymers are characterized by their three dimensional spheric structure and large number of end-groups, which makes them easy to be tailored for various end-user's purposes using different routes compared with their linear counterparts. In present thesis, a series of amphiphilic block copolymers based on hydroxyl end-capped dendritic poly(ether-amide) (DPEA-OH) were prepared and characterized. Their crystallization, temperature-sensitive and encapsulation and control release behaviors were also investigated in detail.1. Synthesis of amphiphilic poly(ether-amide) dendrimer endcapped with poly(ethylene glycol) grafts and its solubilization to salicylic acidAn amphiphilic dendrmer (DPEA-PEG) grafting polyethylene glycol (PEG) at the terminals was prepared by endcapping of DPEA-OH with isocyanate terminated linear polyethylene glycol (PEG-NCO). The molecular structure was verified by gel permeation chromatography (GPC), 1H NMR and FT-IR measurements. The micelle characteristic of DPEA-PEG in water was investigated. The critical micelle concentration (CMC) was determined by a fluorescence technique to be 55.5 mg/L. The hydrodynamic radius of micelles was measured by dynamic light scattering (DLS) to be 76.2 nm. The UV-visible spectrum showed that the solubility of salicylic acid increased from 1.91 mg/L to 2.78 mg/L when the concentration of DPEA-PEG attained 5 mg/mL in an aqueous solution.2. Crystallization behavior of star-shaped amphiphilic block copolymer based on dendritic poly(ether-amide)The star-shaped amphiphilic block copolymer (DPEA-PCL-PEG) was prepared through ring opening polymerization of s-caprolactone (CL) initiated by hydroxyl end-capped DPEA-OH, then coupling with monomethoxy-terminated PEG via an esterification process. The molecular structure was verified by FT-IR, 1H NMR and GPC measurements. The number average molecular weight of the PCL arm was calculated to be about 1,910 g/mol by 1H NMR analysis. The number average molecular weight of the copolymer was determined to be 74,020 g/mol with the molecular weight distribution of 1.15 by GPC. The DSC and X-ray diffraction analysis indicated that the copolymer possesses double melting and crystallization peaks, attributed to PCL and PEG segments in DPEA-PCL-PEG. The corresponding melting and crystallization temperature, and value of crystallinity are much lower than that of their individual homo polymers.3. Encapsulation and controlled release of daidzein using biodegradable star-shaped amphiphilic block copolymer based on dendritic poly(ether-amide)The star-shaped block copolymer (DPEA-PCL-PEG) was found to easily form the micelle-like nanoparticles in water with a lower critical micelle concentration of 5.524 mg/L due to its amphiphilic characteristic, which was confirmed by the fluorescence and DLS techniques as well as transmission electron microscopy (TEM) observation. Daidzein, a hydrophobic traditional Chinese medicine, was efficiently-encapsulated during the particle formation. The optimal feeding concentrations of daidzein and star-shaped amphiphilic block copolymer were determined to be 9.1×10-6 g/mL and 0.5 mg/mL, respectively, which allowed 84.6% daidzein encapsulated. The micelles loaded with daidzein showed a slow drug release speed in the presence of Lipase PS.4. Synthesis and thermally responsive characteristics of dendritic poly(ether-amide) grafting with PNIPAAm and PEGThe thermally responsive dendritic core-shell polymers DPEA-PNIPAAm and DPEA-PNIPAAm-PEG were prepared based upon DPEA-OH, modified with carboxyl end-capped linear poly(N-isopropylacrylamide) (PNIPAAm-COOH) or both PNIPAAm-COOH and carboxyl end-capped methoxy PEG (PEG-COOH) in different ratios via an esterification process. Their molecular structures were verified by GPC, and 1H NMR and FT-IR spectroscopy. The temperature-dependent characteristics study has revealed that DPEA-PNIPAAm exhibits a lower critical solution temperature (LCST) of about 34℃, whereas DPEA-PNIPAAm-PEG polymers with the PNIPAAm/PEG ratio of about 1.0 and 0.4 possess about 36℃and 39℃, respectively, compared with 32℃for homopolymer PNIPAAm. The critical aggregation temperature was investigated using fluorescence excitation spectrum of pyrene as a sequestered guest molecule based upon the sharp increase in I338/I333 value.5. Temperature sensitivity and drug encapsulation of star-shaped amphiphilic block copolymer based on dendritic poly(ether-amide)The star-shaped amphiphilic block copolymer (DPEA-PCL-PNIPAAms) with different PCL block lengths were prepared through ring opening polymerization of CL initiated by hydroxyl end-capped DPEA-OH, then coupling with PNIPAAm-COOH via an esterification process. The molecular structure was characterized by FT-IR, 1H NMR and GPC analysis. As the copolymer dissolved in water, the core-shell structural nanoparticle was formed as a micelle, and confirmed by the fluorescence, 1H NMR and DLS measurements. The optical transmittance and US-DSC measurements demonstrated that the micelles performed the reversible dispersion/aggregation behavior in response to temperature through the outer PNIPAAm polymer shell. The micelles loaded with daidzein showed a much rapid drug release speed at the temperature above the LCST due to the temperature-induced structural change of the polymeric micelle.
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