New results of the self‐initiation mechanism of SH/En addition polymerization

Abstract

No radicals are formed in bis(mercaptopropionate)-diene-mixtures, as shown by means of ESR spectroscopic investigation. Radicals are produced spontaneously only in the presence of triethylene glycol dithiol. The hydrogen-bonded structure of the dithiopropionates is obviously responsible for the inhibition of the charge transfer interaction with the diene compounds and prevents subsequent radical formation. The I3C NMR spectra confirm the anti-Markownikow structure of the polymers formed with diallyl succinate and diallyl terephthalate. ZUS AMMENFASSUNG:Durch ESR-spektroskopische Untersuchungen an Bis(mercaptopropionat)/Dien-Mischungen konnte gezeigt werden, daB durch die Ausbildung einer Wasserstoffbriickenstruktur in den Bis(mercaptopropionat)en die Selbstinitiierung der Monomermischungen unter Oligomerbildung inhibiert wird. Erst nach Zugabe von Triethylenglykoldithiol lassen sich Thiylradikale spontan nachweisen, die infolge der CT-Wechselwirkung mit dem Dien entstehen. Die anti-Markownikow-Struktur der mit Diallylsuccinat und Diallylterephthalat gebildeten Polymeren wird durch 13C-NMR-Analyse belegt.

Characteristics of the photochemical prevulcanization in a falling film photoreactor

“…Well known thiol‐ene reactions involve the reaction of unsaturated CC bonds with thiol derivatives such as alkyl thiols, thiol glycolate esters, or thiol propionate esters. From previous publications, it can be obtained that thiols based on propionate esters and glycolate esters comprise a higher reactivity compared with alkyl thiols due to a weakening of the thiol moiety by hydrogen bonding of the thiol hydrogen groups with the ester carbonyl 18, 31. Due to their commercial availability and widespread use, trimethylolpropane tris(3‐mercaptopropionate) (TriThiol) and pentaerythritol tetra(3‐mercaptopropionate) (TetraThiol) were used as crosslink agents in the photochemical prevulcanization.…”

Thiol‐ene photopolymerization of polymer‐derived ceramic precursors

“…Radicals are most commonly introduced into the system or initiated via typical radical photoinitiators, such as benzophenone or 2,2-dimethoxy-2-phenyl acetophenone (DMPA), 9,10,13 although radicals may also be generated without the presence of any added photoinitiator spe-cies. 13,[17][18][19] Radical termination occurs via bimolecular radical-radical recombinations. 9,20 The thiol-ene polymerization mechanism leads to unique polymerization and material properties relative to other radical vinyl homopolymerizations.…”

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.…”