Digital twins kinetics of virtual free-radical copolymerization of vinyl monomers with stable radicals. 1. Methyl methacrylate

TL;DR

This study extends the digital twins approach to virtual free-radical copolymerization of methyl methacrylate with stable radicals, providing insights into reaction mechanisms and radical behaviors that align with experimental results.

Contribution

It introduces a quantum chemical virtual modeling framework for the initial stage of vinyl monomer polymerization involving stable radicals, expanding previous digital twins applications.

Findings

Stable radicals influence polymerization differently: fullerene C60 captures initiators, TEMPO inhibits monomer radicals.

Virtual kinetic data match experimental observations.

Spin effects are crucial in transition state formation.

Abstract

The first experience of virtual free-radical polymerization of a set of vinyl monomers in the framework of the digital twins (DTs) concept (Polymers 2023, 15, 2999) is extended to methyl methacrylate, copolymerized with small additives of stable radicals such as fullerene C60 and TEMPO. The virtualization of chemical processes is based on the assumption of basic chain reactions that lay the foundation of polymerization. In the current study, a set of elementary reactions, covering the initial stage of the polymerization, is considered. The reactions are the most suitable for quantum chemical treatment. The calculations, covering about 30 DTs, were carried out using a semi-empirical version of the unrestricted Hartree-Fock approximation. The main energy and spin-density parameters of the ground state of DTs are determined. The barrier profiles of three DTs were calculated, which led the foundation for determining the activation energy of the studied processes. The decisive role of spins in the formation of transition states of these processes is confirmed. The two stable radicals behave quite differently with respect to the polymerization of the studied monomer. The action of fullerene C60 concerns mainly the capturing of the initiating free radicals, anchoring them to the molecule body and thus slowing the main polarization process. In contrast, TEMPO effectively capture monomer radicals manifesting itself as a killer of the polymerization thus providing the appearance of the induction period in practice. The obtained virtual kinetic data are in a full consent with experimental reality.