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

Abstract

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 sCO2 compatibility and diffusion), as the foams produced via green sCO2 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 102 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.