The Evolution of Catalysis for Alkyd Coatings: Responding to Impending Cobalt Reclassification with Very Active Iron and Manganese Catalysts, Using Polydentate Nitrogen Donor Ligands

NMR and GPC Analysis of Alkyd Resins: Influence of Synthesis Method, Vegetable Oil and Polyol Content

Alkyd resins are oil-based polymers that have been widely used for generations in the surface coating industry and beyond. Characterization of these resins is of high importance to understand the influence of its components on its behavior, compatibility with other resins, and final quality to ensure high durability. Here, NMR spectroscopy and GPC were used for characterizing differences in the chemical structure, molecular distribution, and dispersity between oil-based and fatty acid-based alkyd polymers made from sacha inchi and linseed oils. Sancha inchi (Plukentia volubilis L.) is a fruit-bearing plant native to South America and the Caribbean, and has a rich unsaturated fatty acid content. The effect of vegetable oil and polyol selection on the synthesis of alkyd resins for coating applications was analyzed. The influence of two different synthesis methods, monoglyceride and fatty acid processes, was also compared. Important structural differences were observed using NMR: one-dimensional spectra revealed the degree of unsaturated fatty acid chains along the polyester backbone, whereas, 2D NMR experiments facilitated chemical shift assignments of all signals. GPC analysis suggested that alkyd resins with homogeneous and high molecular weights can be obtained with the fatty acid process, and that resins containing pentaerythritol may have uniform chain lengths.

Photoactive Fe Catalyst for Light-Triggered Alkyd Paint Curing

Herein, we show that the photoactive complexes [(Cp)Fe(arene)]⁺ (Cp = cyclopentadienyl; arene = C₆H₆, C₆H₅Me) act as latent catalysts that allow for photochemical control over the onset of alkyd paint curing, without the need for antiskinning agents such as the volatile 2-butanone oxime normally used to prevent curing during paint storage. The highly soluble neutral complexes [(Cp)Fe(Ch)] and [(Cp)Fe(Ch')] (Ch = cyclohexadienyl, Ch' = methylcyclohexadienyl) readily convert to the photoactive complexes [(Cp)Fe(arene)]⁺ upon oxidation in alkyd, allowing the latter to be dosed in a wide range of concentrations. Infrared and Raman studies show similar spectral changes of the alkyd paint matrix as have been observed in alkyd curing mediated by well-known, industrially applied cobalt- and manganese-based catalyst Co(neodecanoate)₂ and [(Me₃TACN)₂Mn₂(μ-OOCR)₃](OOCR). The [(Cp)Fe(Ch)]/[(Cp)Fe(arene)]⁺ system performs equally well as these cobalt- and manganese-based catalysts in terms of drying time and outperform the manganese catalyst by showing a hardness development (increase) similar to that of the cobalt-based catalyst. Based on electron paramagnetic resonance and light-activity studies, we propose that photolysis of [(Cp)Fe(arene)]⁺ generates short-lived active Fe^II species, explaining the desired latency. The [(Cp)Fe(Ch)]/[(Cp)Fe(arene)]⁺ alkyd curing systems presented herein are unique examples of intrinsically latent paint curing catalysts that (1) are based on an abundant and harmless transition metal (Fe), (2) do not require any antiskinning agents, and (3) show favorable performance in terms of drying times and hardness development.

Helmet Phthalocyaninato Iron Complex as a Primary Drier for Alkyd Paints

This study describes the catalytic performance of an iron(III) complex bearing a phthalocyaninato-like ligand in two solvent-borne and two high-solid alkyd binders. Standardized mechanical tests revealed strong activity, which appeared in particular cases at concentrations about one order of magnitude lower than in the case of cobalt(II) 2-ethylhexanoate, widespread used in paint-producing industry. The effect of the iron(III) compound on autoxidation process, responsible for alkyd curing, was quantified by kinetic measurements by time-resolved infrared spectroscopy and compared with several primary driers. Effect of the drier concentration on coloration of transparent coatings was determined by UV–Vis spectroscopy.

Modified Ferrocenes as Primary Driers for Formulations of Alkyd Paints

The effect of modification of benzoylferrocene periphery on catalytic activity toward drying of alkyd resins has been investigated by the combination of experimental techniques. A series of substituted ferrocenes have been synthesized and characterized by analytical and spectroscopic tools including X-ray diffraction analysis on single crystals. The electrochemical behavior of the ferrocene derivatives has been elucidated by cyclic voltammetry and rotation disk voltammetry. The activity toward room temperature curing of alkyd resin has been evaluated by standard mechanical tests on coated plates, which enabled to establish a structure/catalytic activity relationship. Fast drying of test coatings has been observed for formulations of (3-methoxybenzoyl) ferrocene. Time-resolved infrared spectroscopy in combination with attenuated total reflectance sampling technique enabled to reveal the kinetic origin of the improved performance for this ferrocene derivative.

Editorial: Cobalt and Iron Catalysis

Cobalt and iron have long history of importance in the field of catalysis that continues to this day [...]