Optically transparent bio‐based polyamides with microcellular foaming properties derived from renewable difunctional aminoamides

Abstract A green approach for the synthesis of bio‐based polyamides (PAs) with a new macromolecular structure was developed. These bio‐based PAs were synthesized by solvent and catalyst‐free polycondensation combining fatty dimer acid Pripol™ 1009 with new difunctional aminoamides (DAAs). The later DAAs building blocks were synthesized by aminolysis of renewable dimethyl sebacate (DMS) and dimethyl adipate (DMA) with three different aliphatic diamines having diverse chain lengths, 2, 4, and 6 carbons. Bio‐based PAs showed M w up to 30,581 g/mol, initial thermal degradation over 380°C, T m from 168.3–202.4°C, T g from 28.3–37.5°C, strain from 36.4 ± 4.0–313.5 ± 2.0%, and tensile strength up to 27.4 ± 0.1 MPa. Interestingly, all the PAs films had excellent optical transparency with cut‐off wavelengths of 276.0–283.0 nm, transmittance from 82.7%–90.7% at 600 nm. As a proof‐of‐concept of their usage, one of the PA was shown to be form microcellular foam by the green scCO 2 method. The foams possessed uniform (cell size; 40 μm, foam density; 0.265 g/cm 3 , expansion rate; 7.2) and bimodal (cell size; 24/38 μm, foam density; 0.302 g/cm 3 , expansion rate; 6.5) cell textures depending on their foaming temperatures. This is the first report of bio‐based PA foams and transparent films manufacturing without toxic solvents.