Bio-Based Poly(Imine-Amide) Materials with Dynamic Covalent Adaptable Networks: Toward Conductive Composites and Thermally Moldable Microcellular Foams

Covalent adaptable networks constructed in bio-based cross-linked polymers are used for the thermal-loop process for thermoset materials and composites. In this study, bio-based poly(imine-amide)s (PIAs; biomass content >85%) were synthesized from the lignin-derived monomer vanillin, citrate ester (triethyl citrate), and 1,4-diaminobutane via a condensation reaction. The imide bonds accompanied by a dynamic covalent nature provided PIAs with a satisfactory catalyst-free thermally malleable polymer network. The synthesized PIAs unveil toughness and ductility due to the combined effect of amide and imide structures and become thermally malleable in a few seconds. These PIAs show advanced performance in recyclability (efficient reprocessing) and have excellent foamability (suitable for good sCO 2 compatibility and diffusion), as the foams produced via green sCO 2 batch foaming technology have an expansion ratio of up to 12.1. PIA/multiwalled carbon nanotube (MWCNT) nanocomposites exhibit high electric conductivity (10 –2 to 10 2 S cm –1 in the range of 1–10 wt % MWCNTs), low percolation threshold (0.43%), and excellent EM-shielding properties (above 70 dB at 10 wt % MWCNTs). More promisingly, the electrical conductivity and EM-shielding properties of these PIA/MWCNT nanocomposites are enhanced by forming microcellular structures. This study presents the molecular structure of a green covalent adaptable network with potential foamability and reprocessing ability, which can be used to prepare lightweight nanocomposites with excellent electrical conductivity and EMI-shielding properties.