Exploration In Synthesis Of Complex Architecture Polymers By Controlled/Living Radical Polymerization

The way of preparing complex architecture polymers was opened with the discovery of living polymerization initiated by Szwarc. Radical polymerization is one of the most commonly used methods for the commercial production in the industry. Thus, it is very import to explore the synthesis of complex architecture polymers by controlled/living radical polymerization.1. The synthesis of copolymer poly(itaconic anhydride-co-a-methyl styrene)[P(Ita-co-AMS)] was prepared by precipitation polymerization using isoamyl acetate as the solvent. Molecular weight of copolymer was3,700g·mol-1measured by gel permeation chromatography (GPC). The content of copolymer was conformed by1H Nuclear Magnetic Resonance (NMR) with Ita:AMS=1:1. The copolymers consisted of AMS segments will undergo a thermal degradation mechanism to generate free radical when they were heated to certain temperature. Thus, the copolymers can be used as the macro-initiators. The solution polymerization of BA was used to study the re-initiation property of P(Ita-co-AMS). The saponified P(Ita-co-AMS) was used as the emulsifier to prepare poly(methyl methacrylate-co-trimethylolpropane triacrylate)[P(MMA-co-TMPTA)] seed emulsion and was used as macro-initiator to synthesize poly(methyl methacrylate)-poly(butyl acrylate)[P(MMA)-P(BA)] core-shell particle. The copolymerization of AMS, BA and acrylic acid (AA) were carried out by soap-free emulsion polymerization. In a second step, the copolymer P(AMS-co-BA-co-AA) was used as macro-initiator for the emulsion polymerization of styrene (St) to prepare core-shell particle. The morphology and particle size of seed particle and core-shell particle were observed though transmission electron microscope (TEM). The particle sizes were increased from120nm to220nm for P(MMA)-P(BA) core-shell particle, and from120nm to170nm for P(AMS-co-BA-co-AA)-P(St) core-shell particle.2. P(MMA), poly(methacrylate)[P(MA)] and poly(vinyl acetate)[P(VAc)] were prepare through the solution polymerization as the backbone polymers with the molecular weight P(MMA):19,200g·mol-1; P(MA):31,800g·mol-1; P(VAc)(C):65,700g·mol-1; P(VAc)(D):6,800g·mol-1. The macro-initiators were prepared by the combination of photoinitiator xanthone or isopropylthioxanthone (ITX) to the backbone polymers after ultraviolet (UV) irradiation. Ultraviolet-visible (UV-vis) absorption spectra indicated that the xanthone or ITX was conbined with backbone polymers in reduced state. When using P(VAc)(C) as backbone polymer, the combination ratio increased with the increase of P(VAc) concentration and the Xanthane:VAc unit ratio. The macro-initiators with P(MMA) and P(MA) as backbone polymers can not intiate the St in80℃. When using macro-initiators with P(VAc)(C, D) as backbone polymers, the graft polymers were synthesized by the polymerization of MM A with higher conversion and St with lower conversion in80℃.3. The kinetic studies of oligo(ethylene glycol) methacrylate (OEGMA8.9), dimethyl amino ethyl methacrylate (DMAEMA) and butyl methacrylate (BMA) were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization using4-Cyano-4-[(dodecylsulfanylthiocarbonyl) sulfanyl]pentanoic acid (DTTCP) as chain transfer agent. The studies suggest the RAFT polymers of these monomers were in good control. Under certain condition, the reaction times when monomer conversions reached80%were estimated. RAFT polymerizations were used to prepare the arm polymers with different properties:hydrophilic P(OEGMA8-9), cationizable P(DMAEMA) and hydrophobic P(BMA). A heterogeneous polymerization process was then involved to cross-link a mixture of the different arm polymers (macro chain transfer agent) into mikto-arm star polymers. The polymerizations using ethylene glycol dimethacrylate (EGDMA) as cross-linker were performed with an automated parallel synthesizer. Various parameters were studied to understand the formation of star polymers. These include the molar ratios of cross-linker, the concentration of arm polymers and the ratio of spacing monomers. When using a redox-cleavable cross-linker, disulfide dimethacrylate (DSDMA), the polymerizations were prepared in ampules, and the mikto-arm star polymers can be cleaved to linear polymers by adding tributylphosphine into star polymers solution. GPC traces show both formation and cleavage of star polymers. The molar ratios of cross-linker and the ratio of different arm polymers were studied. After quaternized by methyl iodide (Mel), the aqueous solution properties of star polymers were learned by atomic force microscope (AFM) and dynamic light scattering (DLS). The AFM images reveal nanoparticles with sizes in the range30to180nm and DLS analysis shows a broad distribution with145nm in particle size. This indicates that the mikto-arm stars have self-assembled into larger micellar agglomerates under the conditions used in DLS and AFM sample preparation.4. A library of functional (fluorescence, anti-cancer, hydrophobic, hydrophilic and cationizable) linear macro RAFT agents were established by RAFT polymerization to prepare multi-functional mikto-arm star polymers. Using an arm-first approach,17recipes were performed to the RAFT copolymerization with the different combination of arm polymers and [DSDMA]:[M-RAFT] ratio. The mikto-arm star polymers with P(OEGMA8-9), P(DMAEMA) and P(BMA) were successfully synthesized and analyzed. The arm conversions were low when poly(cholesteryl methacrylate)[P(CMA)] was chosen as the hydrophobic arm polymer. The products with poly(2-methacryloyloxyethyl phosphorylcholine)[P(MPC)] arms were failed to have GPC characterization. Blue or green fluorescence was observed when the star polymer solutions were under365nm UV light.The mikto-arm star polymers were cleaved to linear polymers on reduction with Bu3P. The P(DMAEMA) arms were quaternized by Mel to provide quaternized star polymers with the ability of binding siRNA as carriers in drug delivery.