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

Abstract

The dynamic behaviors of vitrimer are influenced by the interaction of crosslink 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 (T v ), exchange activation energy (E a ), and Arrhenius prefactor (τ 0 ), with the density of exchangeable hydroxyls was quantitatively discussed. The results indicated that T v and E a were negatively correlated with the density of exchangeable hydroxyls, while τ 0 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 E a , τ 0 , T v , and characteristic relaxation time (τ*) of vitrimer and can also be used as a model for the synthesis of various vitrimer materials.

Mechanically Robust and Chemically Recyclable Polyhydroxyurethanes from CO2-Derived Six-Membered Cyclic Carbonates

“…Thus, CLPHU-DEGDA 80 possesses a lower cross-link density than CLPHU-EGDA 80 , leading to a decrease in T g from 67 to 58 °C. Based on Flory’s ideal rubber elasticity theory (eq ), the cross-link density can be calculated directly from the storage modulus ( E ′) at T g + 50 °C. , CLPHU-EGDA 70 , featuring a shorter-chain diamine structure and the highest TAEA feeding ratio, exhibits the highest cross-link density (315.7 mol/m 3 , Table S2) among the six samples. As shown in Figure d, decrease of the cross-link density leads to a reduction in T g , suggesting that a lower cross-link density is beneficial to activate the mobility of the polymer chain at lower temperatures.…”

“…Due to a range of sustainability and economic driving forces, increasing interests focus on developing renewable polymeric materials to reduce the use of nonrenewable sources. Aminolysis of cyclic carbonate can in situ generate hydroxyls and carbamate, which have been demonstrated to be capable of designing PHU-based vitrimers. , Covalent adaptable networks (CANs) are a cross-link material, but they can flow in response to an external stimulus (temperature, light, etc.). Due to the activation of exchange reactions between dynamic bonds, the topology of the networks can be rearranged.…”

“…The in situ-generated hydroxyls can introduce transcarbamoylation reactions to form covalent adaptable networks (CANs), resulting in the CLPHU vitrimer. Such CANs in the CLPHU vitrimer are allowed to carry out an exchange reaction under the condition of no external catalyst, 17 which avoids the problem caused by poor compatibility of the catalyst in the vitrimer system.…”

Tuning the Dynamics of Enamine-One-Based Vitrimers through Substituent Modulation of Secondary Amine Substrates

“…Several methods have been reported to realize this goal, for instance, tuning the abundance of dynamic motifs, 31,37,38 adjusting the stereoelectronic effects, 4,39,40 incorporating multiple associative dynamic chemistry, 41,42 and so on.…”

“…As such, the molecular tuning of dynamics with a wide window and in a catalyst-free manner would be desirable. Several methods have been reported to realize this goal, for instance, tuning the abundance of dynamic motifs, ,, adjusting the stereoelectronic effects, ,, incorporating multiple associative dynamic chemistry, , and so on. Recently, Kalow and co-workers reported a series of Meldrum’s acid crosslinkers that allows for the tuning of the stress–relaxation rate in the range of 4 orders of magnitude .…”