Structure Design And Synthesis Of Novel Polymer Nanoparticles

Recently, the design, synthesis and application of polymeric nanomaterials becomes one of the most attended research subjects in the world. Polymer nanomaterials refer to polymer materials which have at least one dimension at nanometer scale. These materials possess a series of different geometries such as spheres, rods, tubes, lines,dendrimers and layers. Polymer nanoparticles are polymer nanomaterials with spherical or approximately spherical geometries, such as solid spheres, hollow spheres, porous spheres, capsules, vesicles, dumbbells and onions. Their size is at mesoscopic scale. As a result, they have a lot of unique properties, such as surface effect, volume effect,quantum size effect and macroscopic quantum tunneling effect. Besides, compared with inorganic nanoparticles, polymer nanoparticles possess excellent designability at the molecular level. That is, the structures and functional groups of polymer nanoparticles can be accurately manipulated by the selection of monomer, synthetic route and polymerization method. Such designability results in a lot of special functions, such as sensing, catalysis, stimuli-responsive properties, storage function and drug loading function. Due to these properties and functions, polymer nanopartilces have a wide range of application prospect in chemical industry, biomedicine, electromagnetics,optics, materials science, environmental protection and other fields.Although there have been a lot of research in the synthesis of polymer nanoparticles,some defects still exist. Firstly, it is still difficult to control the structure of polymer nanoparticles and the location of functional groups accurately. Secondly, some synthetic methods require complicated steps and harsh conditions, are not easy to achieve. Therefore, it is necessary to develop more advanced design schemes and synthesis methods. For this purpose, the following research are carried out.1. Novel polymer nanoparticles were synthesized by the intramolecular quaternization cross-linking, and the polymerization of the "nanoparticle monomers"was realized. A core-shell polymer brush was synthesized with grafting onto method by the combination of reversible addition fragmentation chain transfer (RAFT)polymerization and click reaction. There are two blocks in the side chain of the polymer brush, and the interior block contains a certain proportion of 4-vinyl pyridine repeating units. After adding halohydrocarbon crosslinking agent, the intramolecular quaternization cross-linking occurred and the polymer brushes became nanoperticles.The outside block of the side chain is composed of polystyrene (PS), which does not take part in the cross-linking reaction. The PS block can prevent the occurrence of intermolecular cross-linking. In a polymer brush, there are two carboxyl groups locating at both ends of the main chain. The polymer nanoparticles can be connected with each other by the reaction of these carboxyl groups, resulting in the formation of nanoparticle chains. This process is similar to the polymerization of monomers, in which the behavior of polymer nanoparticles is similar to that of small molecule monomers.Therefore, such polymer nanopartilces can be named as "nanoparticle monomers".2. Polymer nanoparticles possessing a functional group with a controllable position were synthesized by efficient UV crosslinking under mild conditions. A core-shell structure polymer brush was synthesized with RAFT polymerization and grafting from method. There are two blocks in the side chain of the polymer brush, and the interior block contains azide groups, which are able to conduct nitrene insertion reaction under UV irradiation. The outside block consisting of PS plays a role in avoiding intermolecular cross-linking. After a certain time of UV irradiation in the dilute solution,intramolecular crosslinking occurred and the polymer brushes became nanoperticles.Each nanoparticle contains an exposed carboxyl group on the surface. The polymer nanoparticles can be connected with each other by the reaction of these carboxyl groups,resulting in dimeric nanoparticles. These exposed carboxyl groups can be further modified to provide the possibility for the preparation of new functional materials.3. PS hollow nanospheres were synthesized through living radical miniemulsion polymerization catalyzed by copper acetate. The amphiphilic iniferter agent 2-(N,N-dicarboxymethyl dithiocarbamate) dodecyl isobutyrate (DIBDC) was synthesized. A surfactant was obtained after transforming the carboxyl group of DIBDC into sodium carboxylate. This iniferter surfactant can be used in miniemulsion polymerization.During the polymerization process, copper acetate did not enter the oil droplets, and the dithiocarbamates acted as pseudohalogens, so that the initiation process only occurred at the oil-water interface. Due to the chain transfer in the presence of iniferter agent,propagation reaction also occurred only at the oil-water interface. Therefore, the whole polymerization process was carried out only at the oil-water interface, rather than inside the oil droplets. As a result, hollow nanospheres formed. This convenient method prevents the formation of solid polymer nanoparticles.