Synthesis of highly thermally stable divanillic acid-derived polyamides and their mechanical properties

Divanillic acid (DVA)–based monomers with different side-chains (R = -(CH2)n-1-CH3, n = 1, 4, 8) were synthesized from methyl vanillate. Polycondensation of these monomers with various aromatic diamines yielded a series of aromatic biomass-based polyamides with weight-average molecular weights (Mw) ranging from 50,000 to 110,000 g/mol. Thermogravimetric analysis (TGA) of the polyamides found decomposition temperatures ranging from 378 to 420 °C. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) revealed an amorphous structure. The polyamides with methyl or butyl side chains exhibited a glass transition temperature (Tg) of 221–322 °C, which indicated high heat resistance and thermal stability, while the Tgs of the polyamides with octyl side chains were about 180 °C. The DVA polyamides showed good solubility in common polar organic solvents; their cast films were prepared from dimethylformamide (DMF) solution. Thermo-pressed films of some polyamides were prepared at temperatures over the Tg, revealing maximum tensile strengths of about 63 MPa.