Strong, Reconfigurable, and Recyclable Thermosets Cross-Linked by Polymer–Polymer Dynamic Interaction Based on Commodity Thermoplastics

Abstract

Polymer networks cross-linked by dynamic covalent bonds possess outstanding mechanical and rheological properties and are expected to be potential alternatives to conventional thermosets. However, while many recent studies of dynamically cross-linked thermosets focused on the employment of small molecular cross-linkers, the macro-cross-linking approach and the corresponding thermosets have been less demonstrated. In this work, reconfigurable and catalyst-free thermosets were synthesized by dynamic polymer–polymer interaction based on reversible boronic ester bond, providing simple and efficient access toward materials with improved mechanical strength and toughness in comparison to related commodity thermoplastics. The dynamic exchange of covalent bonds dispersed between polymer chains enables the materials to be malleable, recyclable, and healable under thermal conditions and readily processable with mechanical mixing without solvent. Moreover, the materials’ mechanical and rheological properties could be tuned by changing the cross-linking density. Although the dynamic networks exhibited good resistance against organic solvents, they could be cleaved as triggered by acids or diols and recycled through the de-cross-linking/re-cross-linking pathway. Given the dramatically increasing interest in environmentally sustainable materials, this polymer–polymer interaction mode provides a robust approach to engineering polymers with improved performance compared with the thermoplastic counterparts.

Vitrimers: directing chemical reactivity to control material properties

“…Compared to real vitrimers, such weakly cross-linked thermoplasts show very limited resistance to dissolution by solvents. [66][67][68] In spite of such drawbacks, these 'vitrimerised thermoplasts' have attracted considerable attention, [66][67][68][69][70][71][72][73][74] considering the fact that they can be processed using usual thermoplastic processing techniques, while their properties can be improved in comparison to the bulk thermoplastic counterparts.…”

Boronic Acid Esters and Anhydrates as Dynamic Cross-Links in Vitrimers

“…To eliminate the addition of low-molecular cross-linker, Wang et al [ 92 ] prepared vitrimers by mixing two copolymers, from which one was equipped with 1,2-diol groups, while the other had pendant boronic acid moieties, both in the form of dioxaborolane. These moieties were incorporated using 2,3-dihydroxypropyl methacrylate and 4-vinylphenylboronic acid 1,2-propanediol ester, respectively.…”

A Tough and Self-Healing Polymer Enabled by Promoting Bond Exchange in Boronic Esters with Neighboring Hydroxyl Groups

“…Taking advantage of the strong and dynamic boronic ester bonds as cross-linking sites, the resulting dynamic covalent 3OH-PBM polymers not only possess excellent self-healing ability under ambient conditions without any external stimulus (water, heat, light, etc.) but also achieve great mechanical strength and toughness simultaneously, which have never been reported in other relevant literatures (see Figure e, as well as Table S2 in the Supporting Information). ,,− ,,,− …”