Peroxide-Free and Amine-Free Redox Free Radical Polymerization: Metal Acetylacetonates/Stable Carbonyl Compounds for Highly Efficient Synthesis of Composites

Abstract

New peroxide-free, amine-free, and phosphine-free redox free radical polymerization (RFRP) initiating systems comprising remarkably stable (i) metal acetylacetonates (Mn­(acac)3, Cu­(acac)2) and (ii) carbonyl compounds bearing labile hydrogen in the α-position are presented for polymerization initiation under mild conditions (under air, at room temperature, nonpurified monomers). The systems proposed in this work are competitive or even outranked the well-known peroxide-based RFRP reference in several criteria: (i) toxicity, (ii) stability, (iii) surface curing, (iv) overall double-bond conversions, and (v) workability of the RFRP mixture (longer gel times are now possible). Radical initiating reactions are studied using many complementary experimental/theoretical techniques: optical pyrometry, thermal imaging, Raman confocal microscopy, electron spin resonance (ESR), ESR spin trapping (ESR-ST), high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), density functional theory (DFT), simulations of bond dissociation energies (BDE), reaction enthalpies, and DFT simulations of seven unknown ESR-ST adducts. A full consistent picture of the chemical mechanisms involved in these new redox systems is provided.

Recent advances on ferrocene-based photoinitiating systems

“…Over the years, a wide range of families have been designed and synthesized as efficient photoinitiators of polymerization, activable under visible light and even under low light intensity. Among these structures, naphthalimides, [40,[52][53][54][55][56][57][58][59][60][61][62] copper complexes, [63][64][65][66][67][68][69][70][71][72][73] flavones, [20,74] iron complexes, [75][76][77][78][79] iodonium salts, [80][81][82] coumarins, [83][84][85][86][87][88][89], acridine-1,8dione, [90][91] iridium complexes, [92][93][94][95][96][97]…”

Performance of Manganese(III) Acetylacetonate in Solvent-Borne and High-Solid Alkyd Formulations

“…This work is focused on application of manganese(III) acetylacetonate (Mn, Scheme 1, Formula a). Such compound is known as initiator of radical polymerizations [15][16][17][18], mediator in organic synthesis [19,20] and catalyst of oxidation reactions [21,22]. Patent literature reports application of acetylacetone solution of Mn in alkyd-based paints, where it performs as the primary drier [23].…”

Recent Advances on Copper Complexes as Visible Light Photoinitiators and (Photo) Redox Initiators of Polymerization

“…In 2018, mechanosynthesis was applied to the synthesis of photoinitiators activatable under near infrared light [69]. Indeed, on the basis of an interesting reaction discovered in 2016, where the grinding of copper (II) acetylacetonate (Cu(acac) 2 with 2-diphenylphosphinobenzoic acid (2-dppba) could give rise to a ligand exchange combined with a modification of the oxidation degree of Cu and the release of an acac• radical (see Figure 25) [70,71,[120][121][122], this approach based on a redox reaction was named metal acetylacetonate-bidentate ligand interaction (MABLI). Optically, reaction between Cu(acac) 2 can be easily detected in solution, the initial blue solution turning green upon addition of 2-dppba.…”