Photochemistry of Tetraphenyldiboroxane and its Use as Photopolymerization Coinitiator,

Abstract

2-Hydroxyethyl methacrylate (HEMA) was photopolymerized in the presence of Safranine (SfH(+)) and tetraphenyldiboroxane (TPhB). Polymerization results are correlated with the photochemistry of TPhB and its ability to aggregate forming hydrophobic domains (critical aggregation concentration, cac, 1.2 × 10(-4) M). Polymerization was not observed when the TPhB concentration was below the cac, indicating that the polymerization is initiated in the hydrophobic environment. The quenching of the triplet state of SfH(+) by TPhB and the generation of the semireduced species of SfH(+) suggests an electron transfer from the boron compound to the excited dye, and that the resulting boron-centered radical initiates the polymerization process.

Ion-Pair Complexes of Pyrylium and Tetraarylborate as New Host–Guest Dyes: Photoinduced Electron Transfer Promoting Radical Polymerization

“…Đ values around 1.3–1.4 indicate a nonconventional value for free radical polymerization as previously observed in other studies with HEMA. ,, Actually, Đ values less than 1.5 are usually observed in specific and controlled polymerization reactions such as reversible addition–fragmentation chain-transfer polymerization (RAFT), atom transfer radical polymerization (ATRP), and ring-opening metathesis polymerization (ROMP) that allow accurate control over the molecular weight and length. − …”

Polymerization Rate Modulated by Tetraarylborate Anion Structure: Direct Correlation of Hammett Substituent Constant with Polymerization Kinetics of 2-Hydroxyethyl Methacrylate

“…where dH t is the reaction heat evolved at dt and ΔH 0 is the heat evolved assuming total conversion (ΔH 0 = 60 kJ mol −1 ). 35,43 The polymerization rates at various initial conversion stage were determined for the different tetraarylborate structures. The corresponding polymerization rates at different times of irradiation are shown in Figure 4.…”

“…Polymerization measurements in the presence of different tetraarylborate were performed by isothermal photocalorimetric analysis at 303 K under irradiation in the UV-spectra range (λ < 390 nm). The polymerization rate ( R p ) was calculated using where d H t is the reaction heat evolved at d t and Δ H 0 is the heat evolved assuming total conversion (Δ H 0 = 60 kJ mol –1 ). , …”

“…Other conventional photoinitiation systems such as riboflavin/amine ,, or safranine/borinate ,− have been observed with low values of activation energy ( E a < 10 kJ mol –1 ). In this sense, the activation energy found for the tetraarylborate systems reveals a moderate stability against thermal process, also indicating that the use of the tetraarylborate as initiator or co-initiator systems may be useful in polymerization studies where the major polymerization pathway is the photochemical process.…”

“…Electron transfer reactions from the photoinduced excited state of riboflavin represent an important route of free radical formation that in the presence of an electron donor or co-initiator (i.e., amine) may initiate vinyl monomer polymerization. − , Alkylboron derivatives have been used as co-initiators of photopolymerization reactions − as well. The irradiation of the two-component system made by a dye and an alkylboron compound release a free and reactive alkyl radical with subsequent reaction with monomer units, initiating the polymerization process. ,,− …”