Iron-Mediated Homogeneous ICAR ATRP of Methyl Methacrylate under ppm Level Organometallic Catalyst Iron(III) Acetylacetonate

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 1 -azobis (cyclohexanecarbonitrile) (ACHN) with longer half-life period as the thermal initiator, ethyl 2-bromophenylacetate (EBPA) as the initiator, triphenylphosphine (PPh 3 ) 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 (M w /M n = 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.

The fate of copper catalysts in atom transfer radical chemistry

“…At the centre of the ATRP mechanism is a dynamic halogen atom transfer equilibrium modulated by a redox-active transition metal complex (Scheme 1 -KATRP). Complexes of various transition metal ions have been used in ATRP including those of groups 5 (V), 4, 5 6 (Mo), [6][7][8] 7 (Mn), 9 8 (Fe & Ru), [10][11][12][13][14][15][16] 9 (Co) 17 and 10 (Ni) 18 , but the vast majority of studies (~ 65%) utilise Cu. 19,20 [Cu Multidentate, N-donor ligands (L) are typically used to solubilise the copper ion and concomitantly tune the position of the central equilibrium constant (KATRP) by controlling the thermodynamic and kinetic properties of the transition metal complex.…”

Structure-Directing Weak Interactions with 1,4-Diiodotetrafluorobenzene Convert One-Dimensional Arrays of [MII(acac)2] Species into Three-Dimensional Networks

“…1 It has found a widespread application as one of the most common chelating ligands for metal species and various aspects of versatile chemistry of acac complexes have been repeatedly reviewed over the years (for comprehensive books and reviews of the past decade, see refs 2 and 3). The great amount of publications on (acac)M species and, in general, on 1,3diketonate metal compounds relates to their extensive application in materials chemistry (e.g., in polymer industry, 4,5 energy storage devices, 6,7 CVD-, 8−10 FEBID-, 11,12 OLED applications 13,14 ), medicine, 15,16 and in organic chemistry where (1,3-diketonate)M's are broadly employed as efficient catalysts for substantial number of organic transformations. 17 As far as the solid state properties of acetylacetonate metal complexes are concerned, in the crystalline state they exhibit unique mechanical 18 and triboluminescent properties, 19 nonlinear optical (NLO) effect, 20,21 and they form wave-like coordination polymers.…”

Metal Acetylacetonates as a Source of Metals for Aqueous Synthesis of Metal–Organic Frameworks

“…Metal acetylacetonate (acac) complexes that are formed of highly labile acetylacetonate linkers have found widespread use in industry, including in vulcanization of plastics for rubber; , curing processes for coatings (e.g., epoxy resins); − as oxidative reagents for degradation of organic pollutants and also shelf-stable nonwoven fabrics and films used in dippers, wipes, towels and bathmats; as polyvinyl chloride (PVC) stabilizers; and as catalysts in many polymerizations. − For example, Zr­(acac) 4 is used to initiate lactide polymerization and copolymerization for the production of bioresorbable materials; in drug-releasing processes; and to form scaffolds for tissue cultures and in biodegradable implants for surgical use . In most of these processes, metal acetylacetonate complexes are considered green reagents due to their low toxicity and ease of handling in air…”