Boronic Ester Based Vitrimers with Enhanced Stability via Internal Boron–Nitrogen Coordination

Abstract

Boron-containing polymers have many applications resulting from their prominent properties. Organoboron species with reversible B–O bonds have been successfully employed for the fabrication of various self-healing/healable and reprocessable polymers. However, the application of the polymers containing boronic ester or boroxine linkages is limited because of their instability to water. Herein, we report the hydrolytic stability and dynamic covalent chemistry of the nitrogen-coordinating cyclic boronic diester (NCB) linkages, and a new class of vitrimers based on NCB linkages is developed through the chemical reactions of reactive hydrogen with isocyanate. Thermodynamic and kinetic studies demonstrated that NCB linkages exhibit enhanced water and heat resistance, whereas the exchange reactions between NCB linkages can take place upon heating without any catalyst. The model compounds of NCBC-X1 and NCBC-X2 containing a urethane group and urea group, respectively, also showed higher hydrolytic stability compared to that of conventional boronic esters. Polyurethane vitrimers and poly­(urea-urethane) vitrimers based on NCB linkages exhibited excellent solvent resistance and mechanical properties like general thermosets, which can be repaired, reprocessed, and recycled via the transesterification of NCB linkages upon heating. Especially, vitrimers based on NCB linkages presented improved stability to water and heat compared to those through conventional boronic esters because of the existence of N → B internal coordination. We anticipate that this work will provide a new strategy for designing the next generation of sustainable materials.

Solution‐Processable and Thermostable Super‐Strong Poly(aryl ether ketone) Supramolecular Thermosets Cross‐Linked with Dynamic Boroxines

“…[ 3,4,10 ] Therefore, cross‐linking low‐molecular‐weight engineering polymers with dynamic covalent bonds or noncovalent interactions provide an alternative strategy for solving the problems associated with the synthesis and processing of traditional HPEPs. Recently, a large variety of supramolecular thermosets and noncovalently cross‐linked polymeric networks have been fabricated by cross‐linking well‐designed polymers with noncovalent interactions and dynamic covalent bonds such as hydrogen‐bonding interactions, [ 3,4,24–29 ] metal‐ligand coordination, [ 22,25,30–32 ] imine bonds, [ 33–36 ] disulfide bonds, [ 37–39 ] boronic ester bonds, [ 40–44 ] and so forth. Only a few of them have outstanding mechanical strength and thermostability comparable to or similar with those of traditional HPEPs.…”

Highly stretchable covalent adaptive networks enabled by dynamic boronic diester linkages with nitrogen→boron coordination

“…Ito et al found the incorporation of dioxazaborocane linkages could contribute to significant changes in the thermal, mechanical, and optical properties of the original epoxy polymers 13 . Zhang et al revealed the dynamic nature of dioxazaborocane linkages 14 . Similar to dioxaborolane linkages, dioxazaborocane linkages are hydrolytically reversible, undergoing transesterification with boronic compounds, and unstable when exposed to hydrogen peroxides 15 .…”

A Strong and Rigid Coordination Adaptable Network that Can Be Reprocessed and Recycled at Mild Conditions

“…Such recycling features of strong and rigid polymers are superior as compared to similar recycling ways in literature. 2,13,[60][61][62][63][64] PETMP 80-20 -Zn can also be used as binders to prepare recyclable Carbon-fiber (CF) composites. Carbon-fiber (CF) composites have undergone rapid development in recent years for a wide range of industrial applications, such as aerospace, wind power, and sporting goods.…”