Methoxy-controlled dynamic properties in reprocessable and degradable poly(imine-urethane)s and application in electromagnetic wave absorbing nanocomposites

Increasing the number of methoxy groups on dialdehyde urethane monomers systematically enhances the mechanical strength, and stress relaxation of the cured poly(imine-urethane) networks. • The presence of dynamic imine and hydrogen bonds endows all three poly(imine-urethane) networks with scratch repair, reprocessing and degradation capabilities. • MWCNT/poly(imine-urethane) composites demonstrate reversible bond driven patch repair, welding, and shape changing behaviour, offering on-demand adaptability. • The 10% MWCNTs/PIU-2 nanocomposites achieves excellent electromagnetic wave absorption and clean recovery of undamaged MWCNT fillers via degradation. Thermoset polymer nanocomposites are arduous to reprocess, degrade, repair once damaged or reclaim functional fillers, leading to environmental pollution and waste of resources upon reaching the end of service life. Herein, three solid dialdehyde urethane monomers (DAU-1, DAU-2 and DAU-3) with varying numbers of methoxy groups were synthesized and cured with triamine. The cured poly(imine-urethane) (PIU-1, PIU-2 and PIU-3) polymeric matrix exhibits a gradual increase in mechanical, thermal and stress relaxation properties with an increase in the number of methoxy groups. All three poly(imine-urethane) systems demonstrated scratch repair, reprocessing and degradation behaviors due to the presence of reversible imine and hydrogen bonds. Notably, after the second cycle of reprocessing PIU-3, the tensile strength and Young’s modulus were significantly increased by 70% and 49%, respectively, owing to the improved polymer configuration and alignment. The results showed that the activation energy of metathesis degradation and stress relaxation properties of all poly(imine-urethane) were dependent on the imine bond, structural configuration by multiple hydrogen bonds and steric barriers influenced by methoxy and urethane groups. Finally, multiwalled carbon nanotubes coated with poly(imine-urethane) (MWCNTs/PIU-2) with different filler loadings were fabricated, which demonstrated patch repair, welding and shape changing performance as a result of the presence of reversible bonds. Additionally, the 10 wt% MWCNTs/PIU-2 nanocomposite displayed good electromagnetic wave absorption performance with a reflection loss of −34.02 dB at 10.06 GHz and a wide effective absorption band of 3.01 GHz. Meanwhile, the undamaged MWCNT fillers were reclaimed from the nanocomposite by taking advantage of the metathesis cleavability of the reversible imine bonds. Poly(imine-urethane)s (PIUs) were prepared using triamine and synthesized dialdehyde urethane (DAUs) containing different number of methoxy groups, owing to the presence of dual dynamic bonds the resultant MWCNTs/PIU nanocomposites exhibits excellent microwave absorption, degradation, and repairing features. Download: Download high-res image (435KB) Download: Download full-size image