Heat Resistant Fluorenone-based Polyimines as Novel Light-emitting Polymers

Fluorenone-based polyamines, as novel light-emitting polymers, were synthesized by the condensation polymerization of 3,6-dibromo-9-fluorenone with different aromatic diamines by palladiumcatalyzed aryl amination reaction. The structures of the polymers were characterized by means of FT-IR, 1H NMR spectroscopy and elemental analysis. The experimental results show a good agreement with the proposed structures. TGA measurement exhibits that the polymers possess good thermal stabilities with high decomposition temperatures（T5 400 ℃）. Due to the photo-induced intramolecular charge-transfer（ICT） of fluorenone-based polyimines, these polymers show significantly strong photonic luminescence in N,Ndimethylacetamide.

Monolithic polyimine vitrimer/graphene aerogel composites

Graphene-polymer composites have attracted great attention as sensing materials due to their tailorable electrical conductivity, physicochemical properties, and sensitivity to geometric and functional changes.Herein, we report the first example of cylindrical monolithic polyimine vitrimer/graphene composites with excellent mechanical, compressive, rehealable and recyclable, and piezoresistive properties via simple infiltration of polymer monomers into the pores of graphene aerogel followed by thermal curing. The composites exhibit excellent durable compressibility(negligible reduction in the compression properties even after 3000 consecutive compression cycles), rapid recovery to the original size upon stress released,high compressive strength(up to 1.2 MPa), and high conductivity(up to 79 S/m). Excellent piezoresistive properties were observed, displaying consistent and reliable change of the electrical resistance with the compression ratio. Furthermore, rehealing with ~100% recovery of the compressive strength and electric conductivity was achieved under mild rehealing conditions, which is highly desired but has rarely been reported for electronic materials. The facile strategy for fabrication of rehealable monolithic polymer/GAs can open new possibilities for the sustainable development of composites with high electrical conductivity for various applications such as sensing, health monitoring, and movement detection.

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 tran- sitions 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.

Reshapeable,rehealable and recyclable sensor fabricated by direct ink writing of conductive composites based on covalent adaptable network polymers

Covalent adaptable network(CAN)polymers doped with conductive nanoparticles are an ideal candidate to create reshapeable,rehealable,and fully recyclable electronics.On the other hand,3D printing as a deterministic manufacturing method has a significant potential to fabricate electronics with low cost and high design freedom.In this paper,we incorporate a conductive composite consisting of polyimine CAN and multi-wall carbon nanotubes into direct-ink-writing 3D printing to create polymeric sensors with outstanding reshaping,repairing,and recycling capabilities.The developed printable ink exhibits good printability,conductivity,and recyclability.The conductivity of printed polyimine composites is investigated at different temperatures and deformation strain levels.Their shape-reforming and Joule heating-induced interfacial welding effects are demonstrated and characterized.Finally,a temperature sensor is 3D printed with defined patterns of conductive pathways,which can be easily mounted onto 3D surfaces,repaired after damage,and recycled using solvents.The sensing capability of printed sensors is maintained after the repairing and recycling.Overall,the 3D printed reshapeable,rehealable,and recyclable sensors possess complex geometry and extend service life,which assist in the development of polymer-based electronics toward broad and sustainable applications.

Poly(imine-amide)Hybrid Covalent Adaptable Networks via in situ Oxidation Polymerization

Polyimine represents a rapidly emerging class of readily accessible and affordable covalent adaptable networks(CANs)that have been extensively studied in the past few years.While being highly malleable and recyclable,the pioneering polyimine materials are relatively soft and not suitable for certain applications that require high mechanical performance.Recent studies have demonstrated the possibility of significantly improving polyimine properties by varying its monomer building blocks,but such component variations are usually not straightforward and can be potentially challenging and costly.Herein,we report an in situ oxidation polymerization strategy for preparation of mechanically strong poly(imine-amide)(PIA)hybrid CANs from simple amine and aldehyde monomers.By converting a portion of reversible imine bonds into high-strength amide linkages in situ,the obtained hybrid materials exhibit gradually improved Young’s modulus and ultimate tensile strength as the oxidation level increased.Meanwhile,the PIAs remain reprocessable and can be depolymerized into small molecules and oligomers similar as polyimine.This work demonstrates the great potential of the in situ transformation strategy as a new approach for development of various mechanically tunable CANs from the same starting building blocks.