Rheological Characteristics of Cross-Linked Materials with Associative Bond Exchange Mechanisms

Abstract

Vitrimers are a new class of sustainable cross-linked materials with an associative bond exchange mechanism. Bond exchange in vitrimers functions in an addition/elimination pathway, where bond dissociation and reassociation appear to occur simultaneously, as opposed to traditional dynamic covalent bonds that act with discrete distinct, separated steps of bond dissociation and reassociation. Because of these characteristics, network disconnection never occurs in vitrimers, and network topology alternation proceeds with maintaining the constant cross-link density at a temperature greater than the activation temperature of the bond exchange. Some unique rheological properties of vitrimers are highlighted in this review article. The first section summarizes the general relaxation features of vitrimer networks based on temperature-ramp creep test, stress-relaxation test, and temperature-sweep viscoelasticity. The applicability or inapplicability of the time-temperature superposition concept is examined in the latter section, which is vital for understanding the thermorheological simplicity (or complexity) of vitrimer materials.