Reprocessable and highly creep-resistant covalent adaptable networks incorporating azine dynamic cross-links via free-radical polymerization

05 May 2025, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Covalent adaptable networks (CANs) are a promising avenue for replacing conventional, unrecyclable thermosets with reprocessable, more sustainable networks incorporating dynamic cross-links. Azine dynamic chemistry has recently been explored and, thus far, has only been incorporated into step-growth CANs. We developed an azine-based cross-linker with methacrylate end groups, enabling radical-based CAN synthesis. Free-radical copolymerization of this cross-linker with n-hexyl methacrylate yielded robust CANs with full property recovery upon reprocessing by compression molding at 120 °C. The associative azine dynamic chemistry resulted in constant cross-link density across the rubbery plateau, extraordinary creep suppression at temperatures of 190-210 °C, and severely limited stress relaxation at temperatures as high as 200-210 °C; nevertheless, this did not hinder the CAN’s reprocessability by compression molding at 120 °C and 8 MPa pressure. Finally, preliminary injection molding and extrusion experiments at temperatures of 200-210 °C indicated the potential feasibility of these methods for azine-based CAN production.

Keywords

polymer
network
sustainability
vitrimer
covalent adaptable network
recycle
dynamic chemistry
dynamic covalent chemistry
dynamic covalent polymer network
CAN
cross-link
azine
creep
extrusion

Supplementary materials

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Supporting Information
Description
Experimental procedures, ESI-MS spectrum of BBMA, gel content and T_g of neat PHMA and P(HMA-co-BBMA) network, TGA profiles of BBMA and P(HMA-co-BBMA), additional DMA and cross-link density data and plots for P(HMA-co-BBMA), azine metathesis scheme, quantitative creep data for P(HMA-co-BBMA), DMA and cross-link density plots for P(LMA-co-BBMA), creep plots for P(LMA-co-BBMA), image of extruder internal structure.
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