Conventional thermosets cannot be recycled into high-value products because the permanent, covalent cross-links prevent melt-state reprocessing or reshaping. Dynamic, covalent cross-links that have been studied over the past fifteen years offer an avenue to overcome this long-standing challenge in polymer science. Interestingly, reprocessable network materials are rarely reported to have multiple concurrent dynamic mechanisms. Here, we employ either hydroxyurethane or thiourethane dynamic chemistry, both of which are capable of dissociative reversion and associative exchange mechanisms, to produce reprocessable polymer networks. With judicious design of the chemistry, resulting network materials based on either chemistry can achieve full property recovery associated with cross-link density after multiple recycles. Specifically, high boiling point monomers were chosen for hydroxyurethane dynamic chemistry to avoid monomer evaporation during reprocessing; unbalanced stoichiometry was employed in the thiourethane system to suppress side reactions and promote the desired exchange mechanism. The excellent reprocessability achieved in both cases demonstrates the importance of a well-rounded approach to design such dynamic network materials and indicates the potential for developing dynamic polymer networks and network composites that can be recycled for high-value applications.

Reprocessable polymer networks based on dynamic chemistry with concurrent dissociative and associative mechanisms: Judicious design leading to excellent reprocessability

2019 Spring National Meeting

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