Vitrimers: Using Dynamic Associative Bonds to Control Viscoelasticity, Assembly, and Functionality in Polymer Networks

Abstract

Vitrimers have been investigated in the past decade for their promise as recyclable, reprocessable, and self-healing materials. In this Viewpoint, we focus on some of the key open questions that remain regarding how the molecular-scale chemistry impacts macroscopic physical chemistry. The ability to design temperature-dependent complex viscoelastic spectra with independent control of viscosity and modulus based on knowledge of the dynamic bond and polymer chemistry is first discussed. Next, the role of dynamic covalent chemistry on self-assembly is highlighted in the context of crystallization and nanophase separation. Finally, the ability of dynamic bond exchange to manipulate molecular transport and viscoelasticity is discussed in the context of various applications. Future directions leveraging dynamic covalent chemistry to provide insights regarding fundamental polymer physics as well as imparting functionality into polymers are discussed in all three of these highlighted areas.

High‐Performance Vitrimeric Benzoxazines for Sustainable Advanced Materials: Design, Synthesis, and Applications

“…Multifrequency oscillatory scan Rheometry (Figure 10), by observing the point of coalescence of vitrimer functional lines of constant frequency. [184,185,342] Two classes of vitrimers are distinguishable, depending on the position of the vitrimer's T v on the thermogram relative to its T g , [343] which determines the thermomechanical and rheological properties of the vitrimer: [344] (a) Vitrimers having T v greater than T g . If T v is above T g and the material is heated up to its glass transition temperature, it undergoes a transition from a glassy state to a rubbery state.…”

N-Coordinated Organoboron in Polymer Synthesis and Material Science

“…Because of the exploration of sustainable polymers in recent years, , healable and reprocessable resins have been extensively studied. Since they are able to undergo damage repair or be reprocessed under suitable conditions, these advanced materials have a longer service life and higher recycling efficiency and further promote the green ecology of polymer materials. − …”

A Highly Dynamic Covalent Polymer Network without Creep: Mission Impossible?

“…An important distinction here, which has been identified before, relates to the fact whether bond rearrangement requires the prior association of two polymer chains (“bimolecular reaction”, Figure 1b) or if a polymer chain can fragment by itself (“unimolecular reaction”, typically followed by a faster non‐rate determining recombination of reactive ends, Figure 1c). The accurate prediction of the effect of molecular‐level reaction parameters on macroscopic properties (its “dynamic covalent shift”) will thus be highly dependent on the experiment and subsequent interpretation over a wide temperature range [23, 34, 37–41] …”

“…According to the Maxwell relation $${(\eta =\tau G)}$$ , both the relaxation dynamics $${(\approx \tau )}$$ and effective cross‐linking densities $${\left(\approx G\right)}$$ will have an effect on the flow capacity of a dynamic network, which can vary depending on the kinetics ( ν ) and thermodynamic equilibrium ( K eq ) of the chemistry involved [25, 38, 42, 43] . Starting from this fundamental relationship, a plethora of reversible reactions and synthesis methods have been reported and are summarised in several comprehensive reviews on this subject [26, 44–46] .…”