Synthesis\nof High-Molecular-Weight All-Biobased Semiaromatic\nFuran Polyamide and Study on Its Polymerization Process

Biobased monomer furan-2,5-dicarboxylic acid (FDCA) can\nreplace\nterephthalic acid to achieve the synthesis of biobased semiaromatic\npolyamides, but FDCA has the problem of difficulty in increasing polymer\nmolecular weight due to decarboxylation, which affects material properties.\nHence, this study employed a method of synthesizing high-molecular-weight\nsemiaromatic polyamides using FDCA esterification products (DMFD)\nas raw materials. Although this method reduces the activity of monomers,\nit improves the stability of monomers and is currently a commonly\nused method. Therefore, amine-based catalysts that enhance the reaction\nactivity through nucleophilic mechanisms are chosen. A poly(pentamethylene\nfuran amide) (PA5F) series was synthesized by melt polymerization\nusing 2-hydroxypyridine as a catalyst. The product structures at different\npolymerization stages were studied, and the reaction was inferred.\nThe results showed that pyridine catalysts with a nucleophilic ability\nimproved the polymerization activity of DMFD in the early polymerization\nstage while avoiding <i>N</i>-methylation of the terminal\namino group of the oligomers. At the same time, it was revealed that\nin the process of ester amine polymerization under pyridine catalysts,\nthe end ester groups of the polymer will react and transform into\ncarboxyl groups. This causes a decarboxylation reaction in the later\nstage of high-temperature polymerization, resulting in an imbalanced\nend-group ratio, leading to end-group sealing and limiting the molecular\nweight increase. Finally, by optimizing the reaction process formula\nand adding an excess (15 mol %) of pentamethylene diamine (PMD) to\nthe feed, a high-molecular-weight polyamide material with <i>M</i><sub>w</sub> of 150,000 g/mol can be polymerized. The results\nof this study indicate that pyridine catalysts represented by 2-hydroxypyridine\nhave great potential in the preparation of high-molecular-weight semiaromatic\npolyamides.