Free‐Radical stabilizers for the thiol/ene‐systems

Abstract

By means of calorimetric investigations it is shown that dithioVdiene-mixtures show a more or less distinct spontaneous dark reaction, without light and in the absence of initiators. Pyrogallol, hydroquinone and catechol were tested as stabilizers. The efficacy of the stabilizer to transform the radicals resulting from charge transfer interaction of the thiol with the ene component into an inactive species decreases in the order mentioned above. ZUSAMMENFASSUNG:DSC-Untersuchungen von DithioVDien-Mischungen zeigen, daB diese Systeme unter Lichtausschlun und in Abwesenheit von Sauerstoff eine mehr oder weniger deutlich ausgepragte Dunkelreaktion aufweisen. Als Stabilisatoren wurden Pyrogallol, Hydrochinon und Brenzkatechin getestet. Ihre Wirksamkeit, die aus der Charge-Transfer-Wechselwirkung des Thiols mit dem Dien resultierenden Radikale zu desaktivieren, sinkt in der genannten Reihenfolge.

Thiol–enes: Chemistry of the past with promise for the future

“…There have been several efforts since the late 1970s to revive the use of thiol-ene photopolymerization in industrial applications, including those of Klemm and coworkers [13][14][15][16][17][18][19][20][21][22] in Germany and early and mid 1990s, Jacobine, Woods, and coworkers [23][24][25][26][27][28][29][30][31][32][33][34][35] in the United States in the early 1990s, and Toh and coworkers [36][37][38][39][40][41][42] in Australia beginning in the mid 1990s. Perhaps the most successful industrial use of thiol-ene photopolymerization since the 1970s era has been by Norland Products, which has successfully marketed photocurable thiolene optical and electronic adhesives for a number of years (the details of their use in technical applications is discussed later).…”

Bulky Guanidinato Nickel(I) Complexes: Synthesis, Characterization, Isomerization, and Reactivity Studies

“…Many publications devoted to studies of model reactions for free radical addition polymerizations of polyfunctional thiols with enes have concentrated on the UV, solid‐state or solution polymerization of these systems 1–15. The emphasis of these studies has included investigations of the microstructure of the products, the effect of photolysis wavelength on the microstructure, or the physical properties and conductivity of the polymers 1–10.…”

“…The emphasis of these studies has included investigations of the microstructure of the products, the effect of photolysis wavelength on the microstructure, or the physical properties and conductivity of the polymers 1–10. Work has also been reported on the reactions in the dark and the effects of stabilizers and peroxide‐induced polymerizations relating to the addition of thiols to enes 11–17. Synthesis of novel soluble conjugated polymers produced by the thiol–ene reaction have also been reported 18…”

An efficient nonisocyanate route to polyurethanes via thiol‐ene self‐addition

“…The limited shelf‐life stability of thiol–enes may be also caused by a base‐catalyzed nucleophilic addition of thiol to the ene double bond . Recently, Liska and coworkers described an efficient stabilizer system for thiol–ene formulations based on the combination of a free radical scavenger and an acid with an appropriate p K a value.…”

“…The limited shelf-life stability of thiol-enes may be also caused by a base-catalyzed nucleophilic addition of thiol to the ene double bond. 48,49 Recently, Liska and coworkers 50 described an efficient stabilizer system for thiol-ene formulations based on the combination of a free radical scavenger and an acid with an appropriate pK a value. Thus, the combination of a moderately strong acid coadditive such as the phenyl phosphonic acid (pK a 5 2) with a small amount of pyrogallol (0.1% wt) was also tested for AMC.…”