Synthesis of High-Molecular-Weight All-Biobased Semiaromatic Furan Polyamide and Study on Its Polymerization Process

Biobased monomer furan-2,5-dicarboxylic acid (FDCA) can replace terephthalic acid to achieve the synthesis of biobased semiaromatic polyamides, but FDCA has the problem of difficulty in increasing polymer molecular weight due to decarboxylation, which affects material properties. Hence, this study employed a method of synthesizing high-molecular-weight semiaromatic polyamides using FDCA esterification products (DMFD) as raw materials. Although this method reduces the activity of monomers, it improves the stability of monomers and is currently a commonly used method. Therefore, amine-based catalysts that enhance the reaction activity through nucleophilic mechanisms are chosen. A poly(pentamethylene furan amide) (PA5F) series was synthesized by melt polymerization using 2-hydroxypyridine as a catalyst. The product structures at different polymerization stages were studied, and the reaction was inferred. The results showed that pyridine catalysts with a nucleophilic ability improved the polymerization activity of DMFD in the early polymerization stage while avoiding N-methylation of the terminal amino group of the oligomers. At the same time, it was revealed that in the process of ester amine polymerization under pyridine catalysts, the end ester groups of the polymer will react and transform into carboxyl groups. This causes a decarboxylation reaction in the later stage of high-temperature polymerization, resulting in an imbalanced end-group ratio, leading to end-group sealing and limiting the molecular weight increase. Finally, by optimizing the reaction process formula and adding an excess (15 mol %) of pentamethylene diamine (PMD) to the feed, a high-molecular-weight polyamide material with M_w of 150,000 g/mol can be polymerized. The results of this study indicate that pyridine catalysts represented by 2-hydroxypyridine have great potential in the preparation of high-molecular-weight semiaromatic polyamides.