Regulating the Dynamic Behaviors of Transcarbamoylation-Based Vitrimers via Mono-Variation in Density of Exchangeable Hydroxyl

The dynamic behaviors of vitrimer are influenced by the interaction of cross-link density and density of exchangeable groups, which results in the difficulty of extracting the effect of mono-variation. In this study, the dynamic behaviors of vitrimer were tuned by changing the density of exchangeable hydroxyls alone, while leaving the cross-link density undisturbed. A multi-hydroxy vitrimer network without a loading catalyst was synthesized successfully. Three-armed functionalized polycarbonate, obtained by ring-opening polymerization of 1,3-dioxan-2-one and its derivatives, was treated as a precursor polymer. Afterward, the precursor polymer was converted into vitrimer in a single step by treatment with hexamethylene diisocyanate. When the system with constant cross-link density was established, the accurate effect of the hydroxyl density on the dynamic behaviors could be characterized by stress relaxation. The relationship of essential dynamic behavioral parameters, such as topology freezing transition temperature (Tv), exchange activation energy (Ea), and Arrhenius prefactor (τ0), with the density of exchangeable hydroxyls was quantitatively discussed. The results indicated that Tv and Ea were negatively correlated with the density of exchangeable hydroxyls, while τ0 showed a positive correlation. In addition, linear models were developed to describe the relationship between dynamic behaviors of vitrimer and density of exchangeable hydroxyls. It is expected that the findings can be applied to precisely control Ea, τ0, Tv, and characteristic relaxation time (τ*) of vitrimer and can also be used as a model for the synthesis of various vitrimer materials.