Construction Of Smart Nanocarriers From Photo-controllable Double Hydrophilic Block Copolymers

Nanocarriers have attracted much interest in recent years due to their promising applications in diverse fields such as catalysis, material preparation and biomedicine. In this dissertation, a series of photo-responsive block copolymer nanocarriers were fabricated via different non-covalent interactions with diverse chemical architectures. This dissertation focuses on the pohoto controllable self-assembly and disassembly of double hydrophilic block copolymers (DHBCs). The details are given in the following parts:1. A novel photo and thermo double responsive block copolymer was developed to fabricate micelles and reverse micelles in aqueous solution. The block copolymer was synthesized by ATRP block copolymerization of a spiropyran-containing methacrylate (SPMA) with di(ethylene glycol) methyl ether methacrylate (DEGMMA). By facile control of the photo irradiation and solution temperature, PSPMA-core and PDEGMMA-core micelles can be obtained respectively. The thermo and photo-responsive micelles were used as smart polymeric nanocarriers for controlled encapsulation, triggered release and re-encapsulation of model drug coumarin 102. The double responsive self-assembly and disassembly were tracked by dynamic light scattering (DLS), transmission electron microscopy (TEM) and fluorescence spectroscopy.2. Photo cross-linkable double hydrophilic block copolymer poly(butanedioic acid,1-[3-[(2-methyl-1-oxo-2-propen-1-yl)oxy]propyl] ester)-b-poly(methoxydi (ethylene glycol)methacrylate-co-4-methyl-[7-(methacryloyl)oxyethyloxy] coumarin) (PSPMA-b-P(DEGMMA-co-CMA)) was synthesized via atom transfer radical polymerization (ATRP). The temperature and pH responsive "schizophrenic" micellization behaviors of PSPMA-b-P(DEGMMA-co-CMA)) were investigated to obtain P(DEGMMA-co-CMA)-core and PSPMA-core micelles. After the two types of micelles were exposed to 365 nm UV light, core cross-linked (CCL) micelles and shell cross-linked (SCL) micelles were facilely prepared. The photo cross-linking was proved to be reversibly controlled under alternative irradiation of 365 nm and 254 nm UV light. More interestingly, block copolymer nanogels were fabricated by translating the hydrophobic core of the CCL and SCL micelles into hydrophilic via adjusting the temperature and pH. The sizes, swollen degrees and cross-linking degrees of the block copolymer nanogels can be facilely controlled by UV light irradiation.We also designed reversibly photo cross-linkable pH-responsive block copolymer poly(ethylene oxide))-b-poly(2-(diethylamino)ethyl methacrylate-co-4-methyl-[7-(methacryloyl) oxyethyloxy] coumarin) (PEO-b-P(DEA-co-CMA)). This block copolymer can be used to construct photo cross-linkable pH-responsive nanogels. The nanogels can be served as nanoreactors for the synthesis of gold nanoparticles. The protonated DEA units were first coordinated with HAuC14, and then the electrostatically bounded AuC14-anions were reduced to gold nanoparticles by NaBH4. The catalytic activity of the nanogel-supported gold nanoparticles was further studied.3. Because of the suparmolecular host-guest interactions between photo-responsive trans-azobenzene andβ-cyclodextrin (β-CD), the reversible photo-responsive supramolecular self-assembly and disassembly of vesicles were constructed. Azobenzene-containing block copolymer poly(ethylene oxide)-b-poly (6-[4-phenylazo phenoxy]hexyl methacrylate-co-2-(dimethylamino)ethyl methacrylate) (PEO-b-P(AzoMA-co-DMAEMA)) was successfully designed to explore the self-assembly behavior in aqueous solution. PEO-b-P(AzoMA-co-DMAEMA) can self-assemble into vesicles. The morphologies and sizes of the vesicles can be controlled by copolymerization of hydrophobic AzoMA with different content of DMAEMA. Spherical vesicle-to-compound vesicle-to-irregular vesicle transitions were observed just by facilely adjusting the content of DMAEMA and AzoMA. After the addition of different content ofβ-CD, vesicles were transited to micelles and at last dissociated. Alternating irradiation of the solution with UV and visible light induced the reversible supramolecular self-assembly and disassembly of vesicles because of the photo-induced trans-to-cis isomerization of azobenzene units. The supramolecular self-assembly and disassembly procedure was studied by dynamic light scattering (DLS), transmission electron microscopy (TEM) and UV-vis spectra.