REACTIONS OF ATOMS AND FREE RADICALS IN SOLUTION. XXV. THE REACTIONS OF OLEFINS WITH MERCAPTANS IN THE PRESENCE OF OXYGEN¹

Abstract

Mercaptan-induced polymerization and copolymerization reactions are intimately related to one type of olefin-mercaptan addition reaction, and may be interpreted or profitably studied only on the basis of a fundamental understanding thereof. Although such addition reactions may be classified into at least two basically different types, those relevant to the present discussion are free-radical chain reactions yielding products of anti-Markovnikov configuration (1,2).Chain reactions of the kind specified may be said to involve three essential steps. The first is the generation from the mercaptan (RSH), by any one of a variety of possible means, of mercaptyl (RS•) free radicals. An applicable method and the one most commonly employed, involves the attack of an oxidant (Ox) upon the mercaptan (Equation 1). The second step consists in the additive reaction of a mercaptyl free radical with an olefin molecule (Equation 2). The third step completes the addition through interaction of the derived free radical formed in the second step and a molecule of mercaptan, at the same time regenerating the chain-initiating mercaptyl free radical (Equation 3).1. RSH + Ox-> OxH + RS• 2. R'CH=CH2 + RS• ->R'(RSCH2)CH•

THE INHIBITION OF AUTOXIDATION BY 2,4,6-TRI-tert-BUTYL SUBSTITUTED PHENOL, ANILINE, AND THIOPHENOL

“…It has roughly half the efficiency of AIBN as an initiator. This behavior is similar to that reported for equimolar mixtures of styrene and 4-rnethoxythiophenol in heptane a t roo111 temperature (7). However, in the present case oxidation did not cease after the absorption of less than 1 molar equivalent of oxygen based on the amount of thiophenol (7).…”

“…With tri-t-butylthiophenol, on the other hand, the induction period was only 2 000 s (n = 0.95) and the rate a t the end of this induction period was only about one-third of the uninhibited rate. This rate very slo~vly increased and reached the uninhibited value after about 9 000 s. This suggests that the thiophenol reacts rapidly with only one peroxy radical per inolecule (reaction [GI) and that the thiophenoxy radicals disappear by dinlerization (presumably to the disulfide ( 6 , 11) which inust itself be a very weak inhibitor) rather than by reaction with a peroxy radical (reaction [7]). …”

Evaluation and control of thiol–ene/thiol–epoxy hybrid networks

“…More specifically, the accepted initiation, propagation and termination steps are illustrated below [27,28].…”

Functional off-stoichiometry thiol-ene-epoxy thermosets featuring temporally controlled curing stages via an UV/UV dual cure process

“…Although thiol-ene free-radical chemistry has been described and formulated in earlier work, 6-8 a revival of this chemistry in thiol-ene photopolymerization occurred mainly due to the development of efficient photoinitiators in the late 1970s. 9 Photopolymerized thiol-ene systems offer low shrinkage *These authors contributed equally to this work.…”