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"Living"/Controlled Radical Polymerization In The Presence Of Metal (Salt) And Thioesters

Posted on:2012-05-31Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q F ChenFull Text:PDF
GTID:1221330368491349Subject:Polymer Chemistry and Physics
Abstract/Summary:PDF Full Text Request
“Living”/controlled radical polymerization (LRP) which combines the advantages of free radical polymerization and living polymerization, has attract more and more attention of polymer chemists. Up to date, the iniferter polymerization, nitroxide-mediated polymerization (NMP), reversible addition-fragmentation chain transfer (RAFT) polymerization, atom transfer radical polymerization (ATRP) and single electron-transfer living radical polymerization (SET-LRP) have been developed as the important techniques in LRP field. For different LRP techniques, the way to achieve the“living”/controlled polymerization is the same, that is establishing an equilibrium between the active species and the dormant species. Based on the mechanism, one LRP technique can be transferred to the other which may provide theoretical support to develop a new LRP system with the merits of the both LRP techniques.This thesis is based on the combination of thioesters and metal (salt)/ligands to enlarge and enrich the LRP techniques. The work can be summarized as follows:(1) The catalyst system used in activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP) was added to the RAFT polymerization of MMA at 80 oC using 2-cyanoprop-2-yl dithionaphthalenoate (CPDN) as the chain transfer agent. The polymerization behavior of MMA both in the presence of air and in the absence of air was studied. After the CuBr2/PMDETA (Copper(II) bromide/ N,N,N’,N’’,N’’-pentamethyldiethylenetriamine) was added, the polymerization rate was enhanced, and the conversion of MMA was higher than 90% within 5 hours. The polymerization kept all the characters of“living”/controlled free radical polymerization: the number-average molecular weights (Mn,GPC) increasing linearly with monomer conversion and the molecular weight distributions (Mw/Mn) were narrow. Importantly, the increase of CPDN concentrations accelerated the polymerization rate. 1H NMR spectroscope confirmed that PMMA chain was end-capped by the CPDN moieties and could be reactivated for chain-extension reaction. In this work, CPDN was supposed to act as the pseudohalogen initiator. When a little amount of oxygen was presented, similar results were obtained. Besides, when iron catalyst (Iron(III) chloride hexahydrate, FeCl3.6H2O) was used instead of CuBr2, similar results were obtained.(2) At 110 oC, the polymerization of St was mediated by different chain transfer agents with the addition of CuBr/PMDETA. The chain transfer agents used in this work were 2-cyanoprop-2-yl dithiobenzoate (CPDN), 2-cyanoprop-2-yl dithiobenzoate (CPDB), benzyl dithiobenzoate (BDB) and dibenzyl trithiocarbonate (DBTTC) The polymerization proceeded smoothly. The polymerization rate was enhanced when CuBr/PMDETA was added as well as the increase of chain transfer agent concentrations. Besides, the polymerization kept all the characters of LRP. According to the result, an ATRP dominating mechanism was suggested, wherein the dithioesters and trithiocarbonate acted as the pseudohalogen initiator. Furthermore, the structure of the chain transfer agent had intense influence on the polymerization control: when CPDN and CPDB were chosen as the pseudohalogen initiator, perfect control of the polymerization was observed; when BDB or DBTTC was selected, the molecular weights were deviated from the theoretical ones and Mw/Mn values were relatively high.(3) A non-ATRP catalyst, ferrocene (Fe(Cp)2) was added to the RAFT polymerization of MMA using thermal initiation method, the polymerization was conducted smoothly. Compared to the RAFT polymerization of MMA, the polymerization rate was enhanced when Fe(Cp)2 was added and the polymerization kept all the characters of LRP. It was proposed that the formation of a redox initiation system, with poly(methyl methacrylate) peroxide (PMMAP) generated in situ as the oxidizer and Fe(Cp)2 as the reducer. Such a redox initiation mechanism was further validated with ascorbic acid (VC) as the reducer instead of Fe(Cp)2. An ATRP catalyst, CuBr was added instead of Fe(Cp)2, the polymerization rate was enhanced with the increase of the CPDN concentration. An ATRP dominating mechanism was proposed with CuBr as ATRP catalyst. (4) The single electron-transfer living radical polymerization (SET-LRP) of acrylonitrile (AN) was successfully conducted at room temperature (25 oC) using ethyl 2-bromoisobutyrate (EBIB) as the initiator, 2,2’-bipyridine (Bpy) as the ligand and Cu(0) as the catalyst, respectively. The polymerization proceeded smoothly in dimethyl sulphoxide (DMSO) with higher than 90% conversion in 13 hours and it kept the features of LRP. 1H NMR spectra proved that the resultant polymer was end-capped by ethyl 2-bromoisobutyrate species and could be reactivated for chain-extension reaction. For a better control of the polymerization of AN, the SET-RAFT polymerization of AN was introduced: the GPC molecular weights agreed well with the theoretical ones and the Mw/Mn values were low.(5) The SET-RAFT polymerization of vinyl acetate (VAc) was successfully carried out at room temperature with o-ethyl-S-(1-ethoxycarbonyl)ethyl dithiocarbonate (EEDC) as chain transfer agent, 2-bromopropionoate (MBP) as halide initiator and Cu(0) (or Fe(0)) as catalyst. The polymerization can proceed, however, moderately low monomer conversion was obtained. To enhance the VAc conversion of at room temperature, the RAFT polymerization of VAc was successfully carried out using 60Coγ-irradiation initiation method with EEDC as the chain transfer agent without any thermal or photoinitiators. The polymerization proceeded smoothly in bulk with higher than 90% conversion within 7 hours at an irradiation dose rate of 10 Gy/min and the features of LRP were maintained. The molecular weight distribution (Mw/Mn) kept narrow (Mw/Mn < 1.35) up to 90% conversion, conveying a better control over molecular weights in comparison with RAFT polymerization initiated by thermal radical source. 1H NMR spectra and matrix assisted laser desorption/ionization time-of-flight mass spectrometry confirmed that PVAc chain end was living and can be reactivated for chain-extension reaction.(6) CuBr/PMDETA was added to the s thermal-initiated RAFT polymerization of MMA with CPDN as the RAFT agent at room temperature under 60Coγ-irradiation. The polymerization proceeded smoothly in dimethyl sulphoxide (DMSO) and maintained the features of LRP. Compared to the RAFT polymerization of MMA using 60Coγ-irradiation initiation method, the addition of CuBr/PMDETA can accelerate the polymerization rate. When increasing the CPDN concentration, the polymerization rate decreased. Base on this evidence, a RAFT polymerization dominating mechanism was suggested. Besides, the ATRP of MMA using CuBr2/PMDETA as catalyst was studied under 60Coγ-irradiation at room temperature. The polymerization proceeded smoothly even when the Cu(II) concentration was reduced to 20 ppm level, while keeping good control over molecular weights. This work provided the first example for the ATRP of MMA under 60Coγ-irradiation at room temperature.
Keywords/Search Tags:“Living”/controlled radical polymerization, atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, single electron-transfer living radical polymerization (SET-LRP), SET-RAFT
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