Abstract
Atom Transfer Radical Polymerization (ATRP) is an important polymerization process in polymer synthesis. However, a typical ATRP system has some drawbacks. For example, it needs a large amount of transition metal catalyst, and it is difficult or expensive to remove the metal catalyst residue in products. In order to reduce the amount of catalyst and considering good biocompatibility and low toxicity of the iron catalyst, in this work, we developed a homogeneous polymerization system of initiators for continuous activator regeneration ATRP (ICAR ATRP) with just a ppm level of iron catalyst. Herein, we used oil-soluble iron (III) acetylacetonate (Fe(acac)3) as the organometallic catalyst, 1,1′-azobis (cyclohexanecarbonitrile) (ACHN) with longer half-life period as the thermal initiator, ethyl 2-bromophenylacetate (EBPA) as the initiator, triphenylphosphine (PPh3) as the ligand, toluene as the solvent and methyl methacrylate (MMA) as the model monomer. The factors related with the polymerization system, such as concentration of Fe(acac)3 and ACHN and polymerization kinetics, were investigated in detail at 90 °C. It was found that a polymer with an acceptable molecular weight distribution (Mw/Mn = 1.43 at 45.9% of monomer conversion) could be obtained even with 1 ppm of Fe(acac)3, making it needless to remove the residual metal in the resultant polymers, which makes such an ICAR ATRP process much more industrially attractive. The “living” features of this polymerization system were further confirmed by chain-extension experiment.
Highlights
Reversible deactivation radical polymerization (RDRP) [1–7] including initiator-transfer agent-terminator (Iniferter) [8–11], nitroxide-mediated polymerization (NMP) [12–18], atom transfer radical polymerization (ATRP) or metal-catalyzed living radical polymerization [19–43] and reversible additionfragmentation chain transfer polymerization (RAFT) [44–55] has been used to design and synthesize various polymeric structure and architectures extensively
The most important advantage of ICAR ATRP [60–65] over normal ATRP is that the desired amount of catalyst is significantly reduced because the continuously produced free radicals can reduce the high oxidation transition metal complexes so that the catalyst can remain active during the polymerization process
A predetermined quantity of PMMA obtained by ICAR ATRP of methyl methacrylate (MMA) was added to a clean ampoule, and the determined quantities of MMA (0.2 mL), toluene (1.0 mL), Fe(acac)[3 ], PPh3 and azobis cyclohexanecarbonitrile (ACHN) were added
Summary
Reversible deactivation radical polymerization (RDRP) [1–7] including initiator-transfer agent-terminator (Iniferter) [8–11], nitroxide-mediated polymerization (NMP) [12–18], atom transfer radical polymerization (ATRP) or metal-catalyzed living radical polymerization [19–43] and reversible additionfragmentation chain transfer polymerization (RAFT) [44–55] has been used to design and synthesize various polymeric structure and architectures extensively. The concentration of iron catalyst is relatively high and the polymerization system was heterogeneous due to the use of polar reducing agent ascorbic acid Based on these problems, we try to use an organic iron salt as the catalyst to set up a homogeneous iron-mediated ICAR ATRP suitable for oil-soluble polymerization system, which can be controllable when the amount of catalyst is reduced to ppm level. We used ACHN as the thermal initiator to establish an iron-mediated homogeneous ICAR ATRP system using oil-soluble Fe(acac)[3] as the organometallic catalyst and PPh3 as the ligand This polymerization system provided an efficient homogeneous polymerization of MMA under ppm level of iron catalyst at 90 ̋ C
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