Structure-property insights of semi-aromatic polyamides based on renewable furanic monomer and aliphatic diamines

A series of semi-aromatic polyamides based on a renewable monomer, 2,5-furandicarboxylic acid (FDCA) has been reported. The dimethyl ester derivative of FDCA (DMFDC) was subjected to polymerization with aliphatic diamines differing in carbon chain length, through an environmentally benign melt polycondensation technique using titanium(IV) isopropoxide (TIPT) catalyst at low concentrations (400 ppm). The newly synthesized furan-based polyamides (FPAs) showed molecular weights in the range of M _n = 8–11 kg/mol and M _w = 29–32 kg/mol and high glass transition temperatures (T _g range 97–140 °C). The structure and properties of these FPAs were investigated using various analytical techniques. DSC analysis showed absence of crystallization and melting behaviour, indicating predominantly an amorphous character of these FPAs, which was further confirmed by DMA analysis. However, Poly(butylene furanamide) (PA4F) showed presence of crystalline regions exhibited in the form of several peaks on the WAXD pattern. These peaks were attributed to the isothermal crystallization caused by the annealing effects during synthesis. The FPAs also showed comparable thermal stabilities to their petroleum-based counterparts as measured by the TGA and found to be thermally stable up to 400 °C. Poly(decamethylene furanamide) (PA10F) displayed the highest thermal stability (T _{d- max} = 446 °C). MALDI-ToF MS revealed various end-groups in addition to the expected amino and ester end-groups arising from the side reactions, such as, pyrrolidine (PA4F), N-methylation, decarboxylation and triamine formation. Presence of these end-groups was ascribed to the higher temperature employed for the polycondensation step.