Kinetics of Polymerization Reaction of α,α‘-Bis(tetrahydrothiophenio)-p-xylene Dichloride

Abstract

Polymerization reactions of α,α‘-bis(tetrahydrothiophenio)-p-xylene dichlorides with OH- in H2O have been studied kinetically. The reactions proceeded via the α-tetrahydrothiophenio-p-xylylene intermediates. Results of the H−D exchange experiments and kinetic studies reveal that the 1,6-elimination forming the intermediates proceeds reversibly via the ylide intermediate. The observed rate of disappearance of the intermediate was increased by the addition of OH-, tetrahydrothiophene, and S2O8 2- as well as by the photoirradiation with a tungsten lamp in the presence of Rose Bengal and was inhibited by TEMPO. However, the rate was found to be independent of ylide concentration. From these results, an elimination−free radical polymerization mechanism is proposed. The microscopic rate constants for each step of this mechanism were calculated from the change in the intermediate concentration with time. All of the rate data showed excellent correlations with the substituent constants in the Hammett plot.

Quantifying the Kinetics of the Gilch Polymerization toward Alkoxy-Substituted Poly(p-phenylene vinylene)

“…Alternatively, this reaction proceeds via an E1 CB elimination mechanism, as is generally accepted for e.g. the Wessling precursor route, ,, but density functional theory (DFT) calculations show that an E2 mechanism applies to the Gilch reaction. As mentioned above, the p -quinodimethane dimerizes to give the diradical dimer D (eq 2).…”

“…32,36,37 For the Gilch route performed in THF with potassium tertbutoxide (KO t Bu) as base, it is now generally accepted that the polymerization proceeds via a (free) radical mechanism (see Scheme 1). 38,39 Somewhat surprisingly, and in contrast to other precursor routes, such as the sulfinyl 40−43 and Wessling 44,45 routes, for the Gilch route to date no detailed quantitative studies of the kinetics of the complete polymerization exist in the current literature. A reason for this may be the fact that the Gilch route comprises a complex one-pot reaction cascade, which besides the chain initiation, growth, and termination steps includes halide elimination toward the final conjugated polymer.…”

The Gilch Synthesis of Poly(p‐phenylene vinylenes): Mechanistic Knowledge in the Service of Advanced Materials

“…Also Cho et al, who first favored anionic chain growth, [119] revised his earlier standpoint and has favored radical chain growth since then. [120][121][122] To summarize, the majority of information available supports 1,6-type radical polymerization of the pquinodimethane-type active monomer III as the key step of the Wessling route, and some evidence was reported in favor of spontaneous formation of diradicals VI as the initiators of subsequent radical chain growth.…”

Block-type architectures for Poly(p-Phenylene Vinylene) derivatives: a reality or an illusion?

“…Before, Wessling himself favored more a self-initiated radical polymerization analogous to the proposed polymerization behavior of the parent p-xylylene 7 (Scheme 2). The "Amherst group" shifted later to the proposal of a radical mechanism 8 , which was nicely elaborated by Cho et al 9 . They demonstrated very convincingly that indeed rather radical and not anionic processes are responsible for the formation of the high molecular weight material observed in the Wessling route.…”