Study Of Zero-valent Iron Co-mediated CRP And Its Functionalization

This thesis was based on the previous work of zero-valent iron/reversible addition fragmentation chain transfer(RAFT) agent mediated controlled radical polymerization(CRP) proposed by the same group in which zero-valent iron(Fe(0)) was used as a catalyst and RAFT agent as both initiator and chain transfer agent for the control polymerization of methyl methacrylate(MMA) in the absent of traditional thermal initiator and ligand at ambient temperature. The result indicated that the polymerization was a living/controlled process with high chain-end functionality. Compared with atom transfer radical polymerization(ATRP) transition metal catalysts, the introduction of Fe(0) reduced both toxicity and cost of production. On account of advantages of Fe(0)/RAFT agent catalyzed CRP, this strategy was utilized to control polymerization of functional, sensitive and hydrophilic monomers in this thesis. A kinetic investigation was conducted along with zero-valent metal/RAFT agent catalytic system. Furthermore, magnetic polymeric nanoparticles were also fabricated via this approach. Detailed two parts of work were involved as following:(1) Zero-valent metal/RAFT agent mediated CRP of functional monomersZero-valent iron and RAFT agent 2-Cyanoprop-2-yl 1-dithionaphthalate(CPDN) were used to mediate CRP of glycidyl methacrylate(GMA) without traditional thermal initiator and ligand at ambient temperature. Good livingness of the polymerization was observed with appropriate Fe(0) and CPDN concentrations. Most of the GMA polymer chains were “living” by 1H NMR spectrum and chain extension analysis. Good control polymerization behavior was also observed in Fe(0)/CPDN mediated CRP of 4-vinyl pyridine(4VP) and butyl methacrylate(BMA). Interestingly, the combination of Fe(0) with the hydrophilic RAFT agent 4-(4-cyanopentanoic acid) dithiobenzoate(CPADB) catalyst system can also enable good control polymerization of hydrophilic monomers in aqueous solution, such as 2-(dimethylamino) ethyl methacrylate(DMAEMA) or poly(ethylene glycol) monomethyl ether methacrylate(PEGMA). In some other transition metals, such as Co(0), Ni(0), and Zn(0) instead of Fe(0), good control polymerization behavior was also observed. In addition, tetramethyl-piperidin-1-oxyl(TEMPO) was employed to capture free radicals in polymerization process, and we found that primary radical came from iso-butyronitrile group.(2) Zero-valent iron(Fe(0)) co-mediated RAFT miniemulsion polymerizationThis thesis extended a RAFT polymerization catalyzed by Fe(0) to miniemulsion polymerization and thus proposed an interesting approach to encapsulate magnetic Fe(0) within polymeric shell. The attractive point was that the process did not use any additional initiator, which might be important for the potential biomedical applications. The polymerization demonstrated good control/livingness: linear kinetic plots, linear increased molecular weights, narrow molecular weight distributions and high chain-end fidelity as characterized by size exclusion chromatography, 1H NMR, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Crosslinked uniform PMMA nanoparticles with encapsulated Fe(0) were about 130 nm of diameter as characterized by transmission electron microscopy and dynamic light scattering measurements. The miniemulsion system was stable for up to two months with no obvious flocculation and aggregation of Fe(0). Polymer magnetization curve displayed a ferrimagnetism behavior. This work provides a facile and alternative approach for the fabrication of magnetic polymeric nanoparticles.