Solvent-Free Method for the Copolymerization of Labile Sugar-Derived Building Blocks into Polyamides

This research focuses on the preparation of biobased copolyamides containing biacetalized galactaric acid (GaIX), namely, 2,3:4,5-di-O-isopropylidene-galactaric acid (GaIXMe) and 2,3:4,5-di-O-methylene-galactaric acid (GaIXH), in bulk by melt polycondensation of salt monomers. In order to allow the incorporation of temperature-sensitive sugar-derived building blocks into copolyamides at temperatures below the degradation temperature of the monomers and below their melting temperatures, a clever selection of salt monomers is required, such that the sugar-derived salt monomer dissolves in the other salt monomers. The polymerization was investigated by temperature dependent FT-IR and optical microscopy. The structure of the obtained copolyamides was elucidated by NMR and matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) techniques. The positive outcome of this modified polycondensation method depends on the solubility of sugar-derived polyamide salts in polyamide salts of comonomers and the difference between their melting temperatures, however does not depend on the melting temperature of the used sugar-derived monomer. A variety of comonomers was screened in order to establish the underlying mechanisms of the process.