RAFT Polymerization-induced Self-assembly For The Synthesis Of Nano-objects With Controlled Morphology

Nano-sized materials such as nanospheres, fibers, and vesicles are currently drawing great attention for their potential applications in biomedicine, catalysts, food, analysis, testing and chemical industry. Amphiphilic block copolymers can self-assemble to form spheres, fibers vesicles or other morphologies. Some important parameters that in?uence the morphology of the particles formed by polymerization-induced self-assembly include molar ratio between the hydrophilic and the hydrophobic blocks, the chemical nature of the polymer components, their interactions with each other and with the solvent, p H and salt concentration of aqueous solvent, monomer concentration and so on. In this thesis, we synthesized several types core-shell amphiphilic block copolymers via reversible addition-fragmentation chain transfer(RAFT) aqueous heterogeneous polymerization and systemically studied morphology transition process. In addition, we studied the functionalization of core-shell amphiphilic block copolymer nano-objects. The main contents are listed as follows:1) Core cross-linked star(CCS) polymer is one kind polymer which has a large number of arms connected to a central point or core. Due to the interesting properties such as good solubility and nanometer-size, CCS polymers have been studied in applications for drug delivery, imaging, catalysis, nanoreactors and emulsion. Herein, CCS polymers of poly(N,N-dimethylacrylamide) were prepared and studied as “Macro-CTAs” in emulsion polymerization of styrene. The mass ratio of styrene/CCS and the solid content were systematically varied to elucidate the effect of these parameters on the size and morphology of the particles, which were characterized by TEM and DLS. Control experiments using linear PDMA Macro-CTAs were also performed in order to compare the differences of Macro-CTAs linear PDMA and CCS in mediating emulsionpolymerization. This morphology transformation was unique to CCS-mediated emulsion polymerization.2) While polymerization induced self-assembly(PISA) strategy can be conducted in one step to generate nano-objects with controllable morphologies at high concentrations, it suffers from a general lack of functionality of the core-forming block. Herein, we address this synthetic hurdle by choosing a single commodity monomer(AEMA) to realize multiple functions. AEMA is a commercial monomer bearing reactive b-ketoester groups. The keto group is functionalizable with alkoxylamine(bisalkoxylamine) to form oxime under ambient conditions. Moreover, the b-ketoester can engage in metal complexation. Facile preparation of both nanospheres and vesicles was achieved via polymerization induced self-assembly at solid contents up to 20%. High-yield keto-alkoxylamine chemistry was utilized to decorate and cross-link the nano-objects. Nanoparticles loaded with silver nanoparticles was easy synthesized via silver ion complexation and subsequent reduction. The concept of using a single monomer capable of both morphology control and multifunctionalization is expected to offer significant opportunities in functional nanomaterials.3) The ability to produce PISA-generated nano-objects in water is appealing for economic and environmental reasons. We have been interested in aqueous RAFT dispersion polymerization. However, examples of successful aqueous RAFT dispersion polymerization formulations have been limited due to the special requirement for a soluble monomer that produces an insoluble polymer in water. Therefore, developing new aqueous dispersion polymerization formulations for PISA is essential to expand the aqueous RAFT dispersion polymerization. Herein, we report a novel of aqueous RAFT dispersion polymerization to synthesize ketone-functionalized spheres and vesicles. In order to get vesicles with a remarkable low polydispersity, we developed a strategy to lower thepolymerization rate such that the produced block copolymers had more time to relax and reorganize.