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Iron-Mediated Atom Transfer Radical Polymerization Of Methyl Methacrylate And Styrene

Posted on:2011-08-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:L F ZhangFull Text:PDF
GTID:1101360305473487Subject:Polymer Chemistry and Physics
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Two kinds of novel methods, activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP) and initiators for continuous activator regeneration ATRP (ICAR ATRP) catalyzed by copper, have been developed by combining the advantages of normal ATRP and reverse ATRP. In the two polymerization systems, an alkyl halide is used as an initiator, and a transition metal complex in its oxidatively stable state (Cu(II)) is used as a catalyst. The activators (Cu(I)) with higher activity are produced by the in situ reduction of the copper(II) complexes with nontoxic and easily available glucose, vitamin C (VC), tin(II) 2-ethylhexanoate (Sn(EH)2) and other reducing agents for AGET ATRP or with a conventional radical initiator such as 2,2'-azobis(isobutyronitrile) (AIBN) for ICAR ATRP. It is noted that the reducing agents do not generate initiating radicals but are exclusively used for the reduction of Cu(II) to Cu(I) activating species for AGET ATRP process. In addition, the reducing agents can simultaneously reduce the oxide of a transition metal complex formed with oxygen to activating species, which makes it possible to conduct AGET ATRP in the presence of a limited amount of air. It will be much important for the industrial process.In this dissertation, a series of works about iron-mediated AGET ATRP and ICAR ATRP were conducted in view of the better biocompatibility and low toxicity of iron catalysts as compared with copper ones. And we reported the iron-mediated AGET ATRPs and ICAR ATRP for the first time using VC as the reducing agent, FeCl3.6H2O as the catalyst, triphenylphosphine (PPh3), iminodiacetic acid (IDA) and tris(3,6-dioxaheptyl) amine (TDA-1) as the ligands, ethyl 2-bromoisobutyrate (EBiB), benzyl bromide (BB), 1,3,5-(2'-bromo-2'-methylpropionato) benzene (BMPB) and (1-bromoethyl)benzene (PEBr) as the initiators, methyl methacrylate (MMA) or styrene (St) as the monomer. End-chain analyses and chain extension experiments confirmed the features of"living"/controlled radical polymerization of the iron-mediated polymerization systems. We also applied the iron-mediated AGET ATRP technique to the surface modification of the carbon nanotubes with potential application as biomaterials, and a controlled polymer layer was grafted onto the surfaces.The following conclusions were drawn according to the detailed studies:1. Iron-mediated AGET ATRP of MMA was first developed using FeCl3.6H2O as the catalyst, PPh3 as the ligand, EBiB as the initiator and VC as the reducing agent. It was found that the polymerization rate in DMF was faster than that in toluene; however, the latter polymerization system had better controllability over the molecular weight and molecular weight distribution than the former. The"living"features of the polymerization system were confirmed by analysis of the chain end and chain extension of PMMA.2. A novel iron-mediated AGET ATRP system in DMF was developed using low toxic organic acid of IDA as the ligand, FeCl3.6H2O as the catalyst, EBiB as the initiator, VC as the reducing agent and MMA as the monomer in the presence of a limited amount of air. The kinetics of AGET ATRP of MMA was investigated using different amount of VC in the presence of a limited amount of air, and the plausible polymerization mechanism was drawn correspondingly. The reducing agent VC played a key role for the polymerization of MMA in the presence of a limited amount of air. Increasing the amount of VC increased the polymerization rate of MMA under the same oxygen concentration.3. An iron-mediated bulk AGET ATRP of St was developed using BB as the initiator, FeCl3·6H2O as the catalyst, PPh3 as the ligand and VC as the reducing agent. The kinetics was studied in the absence of oxygen at 110oC. The results showed that the number-average molecular weight of the PS increased with monomer conversion linearly and the molecular weight distribution kept low (PDI = 1.14-1.31), demonstrating the features of"living"/controlled radical polymerization.4. A highly active iron-based catalyst system for the bulk AGET ATRP of St was obtained using FeCl3·6H2O as the catalyst, TDA-1 as the ligand, BMPB as the initiator and VC as the reducing agent in the presence of limited amounts of air. The results of the polymerizations demonstrated the features of'living'/controlled radical polymerization, such as first order kinetic plot, the number-average molecular weights being close to their corresponding theoretical values and increasing linearly with monomer conversion, and narrow polydispersity indices (PDI = 1.18-1.26), and the controlled polymerization of St was also obtained even if 5 mol-% of catalyst was used.5. ICAR ATRPs for St and MMA were developed using FeCl3·6H2O as the catalyst, TDA-1 as the ligand and PEBr as the initiator in the absence of any thermal radical initiator, and the corresponding polymerization mechanism was provided. The results demonstrated that the polymerization of St could be carried out successfully even if the amount of iron catalyst increased to 50 ppm. In the polymerization of MMA, oxygen was used to form in situ thermal radical initiators, MMA peroxides, which were generated from the interpolymerization of molecular oxygen and MMA monomer; therefore it could enhance the polymerization rate of MMA.6. A surface-initiated AGET ATRP system was developed on the surface of multiwall carbon nanotubes (MWCNTs) using FeCl3·6H2O as the catalyst, TDA-1 as the ligand and VC as the reducing agent, and different polymers were successfully grafted onto the surfaces. The core-shell structure of MWCNTs@PS was observed by TEM. Both Raman spectra and the results of hydrolysis of MWCNTs@PS (after extraction by THF) confirmed that the PS chains were covalently tethered onto the surfaces of the MWCNTs. The molecular weights grafted onto the MWCNTs were controlled by the polymerization conditions, but the polydispersity indices were broad (PDI 2.0) due to the special structure of the MWCNTs.
Keywords/Search Tags:iron catalyst, atom transfer radical polymerization (ATRP), AGET ATRP, ICAR ATRP, carbon nanotubes, surface modification, "living"/controlled radical polymerization
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