Synthesis And Characterization Of Bio-inspired Polyimine Composites

Polyimine vitrimers are known for their malleability,which endows these materials with properties such as self-healing,recycling and reshaping due to dynamic-covalent interaction of imine bonds.Polyimine can be conveniently processed by heat-pressing at ambient conditions and self-healed at ambient temperature using solvent.To satisfy the requirements of broader applications,the mechanical properties of polyimine have to be improved by various approaches.Organic-inorganic hybrid composites with excellent properties are widely found in natural materials.Imitation of biocomposite structures,the introduction of inorganic reinforcing phases in polyimine matrices is an effective way to enhance the mechanical properties of polyimine.Herein,bio-inspired polyimine reinforced by three-dimensional?titanium dioxide microspheres?and two-dimensional?graphene oxide?have been successfully prepared through dynamic covalent chemistry,and the amino groups were modified on the surface of the micro-nano reinforcing phase to achieve even distribution in the polyimine matrix.A variety of performances including physicochemical properties,thermal behaviors,mechanical properties and self-healing properties of polyimine matrices and respective composites have been examined to study the enhancement effect and mechanism of three-dimensional and two-dimensional micro-nano fillers.In the study of three-dimensional material reinforced polyimine composites,the successful amino functionalization of TiO₂MS resulted in binding highly active amphiphilic functional groups on their surfaces,which attenuate aggregation of the microspheres and enhance chemical reactivity between the filler and the polyimine matrix.Introduction of optimal amount of amTiO₂MS into polyimine matrix could enhance its tensile strength and modulus without reducing its toughness.The enhancing effect is highly influenced by the distribution of the amTiO₂MS in polyimine matrix.The uniform filler distribution and optimized mechanical properties were obtained at 3%?wt%?addition.The tensile strength and modulus of the composite were enhanced by¹4%and⁹7%,respectively,and tensile toughness is maintained in 4.3±0.86 MJ/m³,which is the same with polyimine.In addition,incorporated with TiO₂MS/amTiO₂MS,the composites retain the self-healing properties of polyimine.A solvent-involved curing process might further enhance the tensile properties of the composites.In the study of three-dimensional material reinforced polyimine composites,the surface of graphene oxide?GO?was successfully modified by diethylenetriamine?DETA?to form a highly active amphiphilic functional groups on the surface,which enhanced the chemical reactivity between the graphene oxide sheet and the polyimine matrix.Using imine covalent dynamic chemistry,amGO was added with different content during the synthesis of polyimine to prepare composites.As a control experiment,GO was added in the same method to prepare composites.Introducing amGO into polyimine matrix can increase its tensile strength,elongation at break and toughness.With the addition of amGO,the tensile strength,elongation at break and toughness of Polyimine-amGO-X increase continuously.When the content of amGO was 1%,the tensile strength,elongation at break and toughness of the composites were enhanced by 86%,130%and 339%,respectively.The dynamic covalent chemical properties of imines give polyimine materials great potential in self-healing and environmentally friendly materials.This article provides a reasonable solution for the preparation of covalently bonded polyimine composites in the future.