Entropy-Controlled Cross-Linking in Linker-Mediated Vitrimers

TL;DR

This paper develops a theoretical framework to understand the phase behavior of linker-mediated vitrimers, revealing entropy-driven reentrant gel-sol transitions and the influence of linker concentration on cross-linking, supported by simulations.

Contribution

It introduces a novel entropy-based model explaining the phase transitions and cross-linking behavior in linker-mediated vitrimers, advancing understanding of their properties.

Findings

Vitrimers undergo reentrant gel-sol transition with increasing linker concentration.

At low temperatures, linker concentration controls the cross-linking degree.

Theoretical predictions match computer simulation results.

Abstract

Recently developed linker-mediated vitrimers based on metathesis of dioxaborolanes with various commercially available polymers have shown both good processability and outstanding performance, such as mechanical, thermal, and chemical resistance, suggesting new ways of processing cross-linked polymers in industry, of which the design principle remains unknown [M. Rottger, et al., Science 356, 62 (2017)]. Here we formulate a theoretical framework to elucidate the phase behaviour of the linker-mediated vitrimers, in which entropy plays a governing role. We find that with increasing the linker concentration, vitrimers undergo a reentrant gel-sol transition, which explains a recent experiment [S. Wu, H. Yang, S. Huang, Q. Chen, Macromolecules 53, 1180 (2020)]. More intriguingly, at the low temperature limit, the linker concentration still determines the cross-linking degree of the vitrimers, which originates from the competition between the conformational entropy of polymers and the translational entropy of linkers. Our theoretical predictions agree quantitatively with computer simulations, and offer guidelines in understanding and controlling the properties of this newly developed vitrimer system.