Bio-inspired Polyimine Copolymers: Facial Integration with High Content Variability and Extremal Transitions of Mechanical Properties

Natural composites have inspired the fabrication of various biomimetic composites that have achieved enhancement on certain mechanical performance. Herein, a facial approach enabled by recent advances in polyimine chemistry has been developed to fabricate bio-inspired hard-soft-integrated copolymers from two polyimines (i.e. PI-H and PI-S) with hardness differential. Subsequent evaluations of multiple mechanical properties on the bio-inspired copolymers with PI-S contents of full-range variability (0 wt%–100 wt%) have revealed extremal transitions for friction coefficients, impact strengths and tensile moduli. More interestingly, the minimum points of friction coefficients show a deformation-resisting response toward the change of applied loads, but not for the altered sliding speeds, suggesting a more significant role of load in determining the optimal anti-friction composition of the hard-soft integrated copolymers. These trends have been further corroborated by scanning electron microscopy of the worn specimens. Together these results have demonstrated that full-range extremal transitions exist on multiple mechanical properties for hard-soft-integrated copolymers, providing valuable insights to the design and fabrication of composite polymers for many applications. The polyimine-based approach outlined here also affords a convenient method to tune the ratio of two components in the copolymers within the full range of 0 wt%–100 wt%, enabling quick integration with high content variability.