Untersuchungen zum mechanismus der thiol‐en‐photoadditionspolymerisation

Abstract

DSC-und ESR-Messungen zur photosensibilisierten Polymerisation von 1,8-Dithio-3,6-dioxaoctan/Phthalsilurebisallylester zeigen, da8 die Reaktion in jedem Reaktionsschritt photoaktiviert erfolgt und da8 C-Radikale intermediilr auftreten. Modelluntersuchungen am System 1 -Octanthiol/Phenylallylether ergaben, da8 bevorzugt Photoaddition eintritt und d& Radikalrekombinationen von untergeordneter Bedeutung sind. Diese Befunde werden durch 'H-, I3C-NMR-und Massenspektren belegt. SUMMARY:DSC-and ESR-measurements during the photosensitized polymerization of 1,8-dithio-3,6-dioxaoctane with phthalic acid bisallyl ester showed that this reaction is photo-activated in each step and that C-radicals do occur. Model studies with the system octane thiol/phenyldlyl ether showed that photoaddition reaction happens and that radical recombinations are of minor signification.

Kinetics of thiol–ene and thiol–acrylate photopolymerizations with real‐time fourier transform infrared

“…Initiation is achieved through the generation of radical centers, the most common method being photoinitiation of the radical centers. Posner1 first discovered the thiol–ene addition reaction in 1905, and the thiol–ene reaction mechanism, polymerization kinetics, and monomer reactivities have since been extensively explored 2–21. Excellent reviews of work in this field were given by Jacobine2 and Woods 3…”

“…The initiation and propagation mechanisms of thiol–ene reactions are thought to be well understood; however, one of the more elusive aspects of thiol–ene polymerizations has been the termination mechanism. Several investigators have proposed different mechanisms and theories about termination and its importance in thiol–ene reactions 2, 4, 6, 7. Termination has been presumed to occur by radical–radical recombination, and in our work, this is assumed to be the primary termination mechanism (steps 5–7) 22.…”

“…Benzophenone and its derivatives have typically been employed as photoinitiators for thiol–ene systems 4, 6, 7, 11–15. As a result, the initiation mechanism of thiol–ene polymerizations with benzophenone is well understood.…”

“…One of the more interesting aspects of thiol–ene polymerizations is that the reaction proceeds readily in the absence of an initiator 18. This results in an instability of thiol–ene systems that has been viewed as a negative trait, requiring most systems to use added stabilizers to improve their stability 2, 3, 6, 7, 19. Using 1 H NMR, Szmant and coworkers10, 23, 24 studied the thiol–ene charge‐transfer interaction and demonstrated that it is responsible for the dark initiation of the reaction via oxygen.…”

Investigation of thermally activated or photoinitiated polymerization by DSC

“…1,8-dithio--3,6-dioxaoctane) and diallylic compounds (e.g. phthalic acid bisallyl ester) [21 ]. The probable chain mechanism without termination reactions is shown for a monofunctional model compound by the following scheme: C 6 H s -CO-C 6 H s + R-SH ~ C6 Hs -COH-C6 Hs + RS 9…”