Radical Formation in Sugar-Derived Acetals under Solvent-Free Conditions.

The degradation of acetal derivatives of the diethylester of galactarate (GalX) was investigated by electron paramagnetic resonance (EPR) spectroscopy in the context of solvent-free, high-temperature reactions like polycondensations. It was demonstrated that less substituted cyclic acetals are prone to undergo radical degradation at higher temperatures as a result of hydrogen abstraction. The EPR observations were supported by the synthesis of GalX based polyamides via ester-amide exchange-type polycondensations in solvent-free conditions at high temperatures in the presence and in the absence of radical inhibitors. The radical degradation can be offset by the addition of a radical inhibitor. The radical is probably formed on the methylene unit between the oxygen atoms and subsequently undergoes a rearrangement.

Structure-Property Relations in New Cyclic Galactaric Acid Derived Monomers and Polymers Therefrom: Possibilities and Challenges.

In order to fully exploit the potential of carbohydrate-based monomers, different (and some new) functionalities are introduced on galactaric acid via acetalization, and subsequently, partially-biobased polyamides are prepared therefrom via polycondensation in the melt. Compared to nonsubstituted linear monomer, faster advancement of the reaction is observed for the different biacetal derivatives of galactaric acid. This kinetic observation is of great significance since it allows conducting a polymerization reaction at lower temperatures than normally expected for polyamides, which allows overcoming typical challenges (e.g., thermal degradation) encountered upon polymerization of carbohydrate-derived monomers in the melt. The polymers derived from the modified galactaric acid monomers vary in terms of glass transition temperature, thermal stability, hydrophilicity, and functionality.

Towards High-performance Materials Based on Carbohydrate-Derived Polyamide Blends.

A bio-derived monomer called 2,3:4,5-di-O-isopropylidene-galactarate acid/ester (GalXMe) has great potential in polymer production. The unique properties of this molecule, such as its rigidity and bulkiness, contribute to the good thermal properties and appealing transparency of the material. The main problem, however, is that like other biobased materials, the polymers derived thereof are very brittle. In this study, we report on the melt blending of GalXMe polyamides (PAs) with different commercial PA grades using extrusion as well as blend characterization. Biobased PA blends showed limited to no miscibility with other polyamides. However, their incorporation resulted in strong materials with high Young moduli. The increase in modulus of the prepared GalXMe blends with commercial PAs ranged from up to 75% for blends with aliphatic polyamide composed of 1,6-diaminohexane and 1,12-dodecanedioic acid PA(6,12) to up to 82% for blends with cycloaliphatic polyamide composed of 4,4'-methylenebis(cyclohexylamine) and 1,12-dodecanedioic acid PA(PACM,12). Investigation into the mechanism of blending revealed that for some polyamides a transamidation reaction improved the blend compatibility. The thermal stability of the biobased PAs depended on which diamine was used. Polymers with aliphatic/aromatic or alicyclic diamines showed no degradation, whereas with fully aromatic diamines such as p-phenylenediamine, some degradation processes were observed under extrusion conditions (260/270 °C).

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 (GalX), namely, 2,3:4,5-di-O-isopropylidene-galactaric acid (GalXMe) and 2,3:4,5-di-O-methylene-galactaric acid (GalXH), 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.