Conjugated polyaniline as a result of the benzidine rearrangement

Abstract

Abstract:The mechanism of the oxidative polymerization of aniline is reviewed on the basis of the experimental evidence and reaction schemes proposed in the literature. It is demonstrated that the balance between the non-protonated and protonated forms of the monomer and the growing chain is responsible for the diversity of the molecular structure, morphology and properties of aniline oxidation products. Various forms are oxidized by two oxidation mechanisms: (1) chain reaction of electrophilic substitution and (2) coupling of cation-radical centres. At pH > 2.5, the non-protonated reagents are oxidized with a chain reaction controlled by electrophilic substitution of the aromatic ring. The reaction leads to the formation of non-conducting aniline oligomers with heterogeneous molecular structures. At pH = 2.5-4, the electrophilic substitution is reduced because of the protonation of the aniline, and the cyclic dimer, phenazine, becomes the main product of the oxidation. The growth of the conjugated chain proceeds at pH < 2.5, when the reactants are protonated. The reaction proceeds through coupling between the terminal cation radical and the monomer cation radical with formation of a -complex. The transformation of the -complex into a para-substituted monomer unit is thermodynamically controlled and is produced through an intramolecular benzidine (semidine) rearrangement. The regular structure of the growing chains is a result of the high regioselectivity of the sigmatropic rearrangements and significant energy gain attained by the formation of protonated polyconjugated chains in the agglomerated state.

Additive‐dependent iptycene incorporation in polyanilines: Insights into the pentiptycene clipping effect and the polymerization mechanism

“…On the basis of the structure and property characterizations of the polymers, we conclude that the feasibility of additive incorporation in the polyaniline polymers is TA > DA ≫ TP. This conclusion could serve as a mechanistic probe of the aniline oxidative polymerization under acidic conditions, particularly the one recently proposed by Stejskal and coworkers . Scheme outlines the chain propagation mechanism for the following discussion.…”

“…This conclusion could serve as a mechanistic probe of the aniline oxidative polymerization under acidic conditions, particularly the one recently proposed by Stejskal and coworkers. [30] Scheme 2 outlines the chain propagation mechanism for the following discussion.…”

“…[29,30] Although the polymerization mechanism remains an open question, it is generally accepted that there exists an incubation period for the in situ generation of nucleates (i.e., the structural cores capable of initiating the polymerization), such as phenazine derivatives 1 and 2 (Chart 1) before the polymer chain propagates. [29,30] While the requirement of nucleate formation might limit the nature of substituents on the aniline monomer, the same requirement provides an opportunity for using external nucleate additives to direct the polymerization toward backbone-modified polyanilines. In this context, understanding the critical structural component of an effective nucleate provides not only a guide for the design of nucleate additives but also insights into the mechanism of chain propagation.…”

Conductive organic polymers: An electrochemical route for the polymerization of dapsone

“…Nonetheless, non-conducting films are typically formed by a few units of impermeable dimers or oligomers, subsequently producing few electroactive sites [9,10], such as in the dimerization of aniline [11][12][13], phenol [14][15][16] and quinones [17][18][19]. In this letter, we report the successful electrochemical synthesis of a conductive dapsone polymer using cyclic voltammetry in a lower potential window and high scan rates.…”

Preparation of conducting polysiloxane/polyaniline composites

“…In their previous work, some of the authors investigated synthesis routes to PANI, its properties and its potential applications, in another, they optimized the synthesis of polysiloxanes, which were subsequently pyrolyzed to silicon oxycarbide glasses . As part of the latter investigations, the authors also prepared polysiloxane composites with epoxy powder as a sacrificial organic filler, in order to obtain highly porous pyrolytic SiOC foams as final product.…”