Rigid, bio-based polyamides from galactaric acid derivatives with elevated glass transition temperatures and their characterization

A comparative study was prepared investigating the synthesis of polyamides using bio-based building blocks derived from sugar beet pulp, namely 2,3:4,5-di-O-methylene-galactarate (GalXH) and 2,3:4,5-di-O-isopropylidene-galactarate (GalXMe) derivatives. Two different approaches towards the synthesis of bio-based polyamides were evaluated: melt polycondensation and direct polycondensation in solution via the phosphorylation technique. The polymerization of GalXMe with diamines resulted in polymers with narrow dispersity whereas GalXH gives polyamides with broad dispersity. Kinetic studies were performed to understand the different behavior of GalXH and GalXMe during polycondensation. The GalX monomers were combined with linear, cycloaliphatic and aromatic diamines, which resulted in amorphous polyamides with glass transition temperatures between 50 °C–220 °C. The obtained polyamides were stable at elevated temperatures (i.e. above 300 °C). The hydrolytic stability of the acetal/ketal groups in the GalX polyamides in different acids (e.g. 5% citric acid, 90% formic acid) was investigated and revealed higher acid resistance of GalXH compared to that of GalXMe. Furthermore, the water absorption of the GalX copolymers was compared to commercial polyamide references.