Polyamides containing a biorenewable aromatic monomer based on coumalate esters: from synthesis to evaluation of the thermal and mechanical properties

A new biobased alternative for terephthalic acid (TPA) in (semi-)aromatic polyamides is proposed, namely 4-carboxybenzene propionic acid (4CBPA). The difference between both monomers is the additional ethylene segment in 4CBPA, which is therefore an asymmetrical monomer. Because of this, differences in the thermal and mechanical properties between 4CBPA and TPA based polyamides are expected. Herein, thermal stability of a 4CBPA model compound was evaluated, and the reactivity difference between the two carboxylic acids of 4CBPA was observed in model reactions. 4CBPA was polymerized with several aromatic and (cyclo)aliphatic diamines via different synthesis methods. Depending on the amine that was used, a different synthesis method is preferred. From a green chemistry point of view, catalyzed melt condensation is the most preferred. The best polymers were further characterized by NMR spectroscopy, IR spectroscopy, TGA, DSC and MALDI-ToF-MS. Additional evaluation of the synthesized 4CBPA polyamides allowed comparison with TPA equivalents. It was found that 4CBPA polyamides with m-xylylenediamine (MXD) and hexamethylenediamine possessed lowered Tg and Tm compared to their TPA equivalents. In case of 4CBPA polyamides with MXD, crystallinity disappears completely. Finally, the tensile properties of one of the 4CBPA polyamides were evaluated in polyamide 12 blends.