Reprocessable Polymer Networks Designed with Hydroxyurethane Dynamic Cross-links: Effect of Backbone Structure on Network Morphology, Phase Segregation, and Property Recovery

Polybutadiene (PB), poly(tetramethylene oxide) (PTMO), and polydimethylsiloxane (PDMS) networks are synthesized using relatively low wt% of dynamic hydroxyurethane cross-links, and recovery of cross-link density, network morphology, and properties are investigated as a function of reprocessing. PB and PTMO networks exhibit full recovery of rubbery plateau modulus, and thus cross-link density, and tensile properties after multiple melt-state recycling steps. PDMS networks exhibit a small loss in rubbery plateau modulus with reprocessing. Small-angle X-ray scattering reveals nanophase separation in PB and PDMS networks. Although PTMO networks are not nanophase separated, cold crystallization is observed, with crystallinity increasing after reprocessing because of chain alignment. This work establishes the effective use of hydroxyurethane cross-links toward full property recovery in different networks and provides insights on the design of reprocessable networks with distinctive morphology and sustainability.