Photoinitiating free‐radical polymerization electron‐transfer pairs applying amino acids and sulfur‐containing amino acids as electron donors

Abstract

A series of free-radical polymerization initiation systems, based on xanthene dyes as the absorbing chromophores [Rose bengal derivative, 3-(3-methylbutoxy)-5,7-diiodo-6-fluorone and 3-acetoxy-2,4,5,7-tetraiodo-6-fluorone] and sulfur-containing amino acids as the electron donors, were investigated. The photoredox pair xanthene dye/sulfur-containing amino acid was effectively used for photoinitiation of free-radical polymerization of the mixture composed of poly(ethylene glycol)diacrylate-1% NH 4 OH (3 : 1). The highest initiating efficiencies were observed for the system composed of methionine derivatives as the electron donor. The mechanism of photoinduced electron transfer between sulfur-containing amino acids and triplet state of xanthene dye was investigated using laser-flash and steady-state photolysis techniques. Based on photochemistry of xanthene dyes, photochemistry of sulfur-containing amino acids, and obtained results, the mechanism describing the major processes occurring during the photoinitiated polymerization by a photoinduced intermolecular electrontransfer process was postulated.

A benzophenone‐naphthalimide derivative as versatile photoinitiator of polymerization under near UV and visible lights

“…Variations around the BP skeleton have been largely explored for many years (and still are). Examples include novel substituted BP structures operating as Type II PIs, cleavable BP derivatives, a series of BP derivatives working as one‐component Type II PIs (working through intra/intermolecular hydrogen‐abstraction), and many types of polymeric photoinitiating systems (PISs) bearing BP moieties . As the absorption of most of these reported systems is not really changed in comparison with that of BP itself, their application remains, however, limited to the UV range.…”

Photoinitiated Polymerization of 2-Hydroxyethyl Methacrylate by Riboflavin/Triethanolamine in Aqueous Solution: A Kinetic Study

“…Riboflavin (RF) absorbs at 444 nm and has been used as a photoinitiator in the polymerization of HEMA along with triethanolamine (TEOHA) as a coinitiator to form a redox pair involved in the process [13–16]. RF is an efficient electron acceptor and meditates in numerous photochemical and biological electron transfer reactions [17–22]. The kinetics of polymerization reactions has been discussed by several workers [12, 23–25].…”

Tetraalkylammonium Salts of Amino Acids and Sulfur‐Containing Amino Acids as Effective Co‐Initiators of Free Radical Polymerization in the Presence of Aromatic Ketones

“…[17] In our previous paper, we described the properties of the series of water soluble initiation systems based on benzophenone sulfonate derivatives acting as electron acceptors and amino acids or sulfur-containing amino acids applied as electron donors. [18] The initial step of this reaction is the formation of a charge-transfer complex between benzophenone triplet and amino acid with the rate constant k q , oscillating in the range of 10 7 -10 9 M À1 Á s À1 . The sulfur containing amino acids can form two charge-transfer complexes, [8] with the radical cation position on, first, the sulfur atom or, second, the nitrogen atom of the amino acid residue.…”

“…Both these forms exist in an equilibrium, but only the first one can lose CO 2 , to form an a-aminoalkyl radical that can initiate polymerization of acrylates. [11,15,18] The triplet excited states of common aromatic ketones are known to have an np à configuration. They are formed by promotion of an electron from a nonbonding (n) orbital of oxygen onto an antibonding p à orbital that is delocalized over the aromatic p system.…”