New sustainable alternating semi-aromatic polyamides prepared in bulk by direct solid-state polymerization

New semi-aromatic bio-based copolyamides PA 4T/4Y and PA 6T/6Y were successfully synthesized in bulk by direct solid-state polycondensation in which hydrophobic bio-based dicarboxylic acids sebacic acid, octadecanedioic or hydrogenated dimer fatty acid (Y = C10, C18 or C36) alternate with terephthalic acid T. The absence of a polymerization solvent and the possibility of performing the polymerization on the dicarboxylic acid make it an interesting route for future production of alternating copolyamides. A stepwise synthetic approach is taken where first terephthalic acid-based diamide diamines of the linear C4 or C6 diamines 4T4 or 6T6 are prepared, followed by preparation of solid salts with the above aliphatic dicarboxylic acids and subjecting the salts to a solid-state post-condensation. The alternation is achieved by the interlocking of the 4T4 or 6T6 units in the salts with the bio-based dicarboxylic acids and polymerizing these salts below the melt temperature of the terephthalamide-based core. During the polycondensation, the transamidation reaction of the terephthalamide moiety is prevented and with that the randomization of the polyamide. Especially the diaminobutane-based PA 4T/4Y copolyamides show strict alternation, leading to interesting properties like high crystallinity and high melting points of 250 to 318 degrees C supported by a randomness value of 2, determined using C-13 NMR spectroscopy. The special alternating feature becomes especially clear when heating the polymer in the melt state, when the transamidation of the terephthalamide moieties is no longer prevented by the interlocking principle, leading to lowering of the randomness value and therewith the melting point and crystallinity. (c) 2020 Society of Industrial Chemistry

Automated summary

New semi-aromatic bio-based copolyamides PA 4T/4Y and PA 6T/6Y were successfully synthesized in bulk by direct solid-state polycondensation. This synthesis route shows potential for producing alternating copolyamides with high crystallinity and high melting points.