The Fundamental and Underrated Role of the Base Electrolyte in the Polymerization Mechanism. The Resorcinol Case Study.

Marco Bonechi,Davide Vanossi,Claudio Fontanesi,Massimo Innocenti

doi:10.1021/acs.jpca.0c07702

Abstract

The Kane–Maguire polymerization mechanism is disassembled at a molecular level by using DFT-based quantum mechanical calculations. Resorcinol electropolymerization is selected as a case study. Stationary points (transition states and intermediate species) leading to the formation of the dimer are found on the potential energy surface (PES), and elementary reactions involved in the dimer formation are characterized. The latter allow to further propagate the polymerization chain reaction, when applied recursively. In this paper, the fundamental role of the sulfate anion (a typical base electrolyte) is addressed. Investigation of the PES in terms of both stationary-state properties and of ab initio molecular dynamics results (dynamic reaction coordinate) allows the appreciation in detail of the critical role of the base electrolyte anion in making the proton dissociation from the initial radical ion, a feasible (downhill in energy) process.

Highlights

Chemistry is well-known as a complex, multifaceted, and nonlinear science,[1] spanning from pure compound characterization to the field of “chemical reactivity”
Electrochemistry is an archetypal field of scientific research where the reductionist approach can lead to interesting results, concerning both faradaic processes and “simple” electrochemical-driven adsorption/desorption interfacial processes.[4−10] Within such an approach, the role of the base electrolyte is in general neglected, as the ideal base electrolyte is both hoped and thought to allow for electrical conductivity in solution without participating in any chemical rection
In this paper the focus is on the resorcinol polymerization mechanism, which is a quite important chemical reaction, in connection with applicative aspects connected to the production of industrial resins.[14−17] resorcinol polymerization must proceed through the dissociation of one hydrogen atom, as it is assumed in resorcinol condensation reactions.[18]

Summary

Introduction

Chemistry is well-known as a complex, multifaceted, and nonlinear science,[1] spanning from pure compound characterization to the field of “chemical reactivity”. A reductionist approach allows the rationalization in detail of the first electron transfer in faradaic processes: for instance, the well-known LUMO energy vs reduction potential relationship.[9] in the case of dissociation reactions following the first electron transfer, a reductionist reaction scheme is able to catch the energy/“molecular structure” relationship This is not the case when a series of complex chemical reactions follow the first charge transfer process, for instance, in the case of electropolymerization reactions, where ample studies are devoted to the determination of the properties of the polymer rather than to the reaction mechanism (which is by far a more complex subject).[11,12] In this field a detailed and successful reaction mechanism rationalization based on only the characteristics of the pristine compounds does not work.[13] in this paper the focus is on the resorcinol polymerization mechanism, which is a quite important chemical reaction, in connection with applicative aspects connected to the production of industrial resins.[14−17] resorcinol polymerization must proceed through the dissociation of one (or two) hydrogen atom, as it is assumed in resorcinol condensation reactions.[18] This is the case for other complex reactive systems, spanning from photochemistry to electrochemistry, where the charge transfer elementary act is coupled with the proton dissociation.[19−22] In our study we focused on the initial reaction steps leading to the formation of dimers. To study the polymerization mechanism, we relied on a steady-state potential energy surface analysis

Methods

Results

Conclusion