Dimer acid-based thermoplastic bio-polyamides: Reaction kinetics, properties and structure

New dimer acid-based-polyamides were synthesized with rapeseed oil-based dimer acid (DA) and 1,2-diaminoethane, 1,6-diaminohexane or 1,8-diaminooctane to form DAPAe, DAPAh and DAPAo, respectively. Effects of diamine chain lengths on kinetics evolution as well as on the thermal, physical and mechanical properties of the different polyamides synthesized were investigated. DAPAo was found to be the most reactive diamine because of its higher nucleophilic character. Differential scanning calorimetry (DSC) combined with X-ray diffraction revealed a low-order semi-crystalline structure for all polyamides. A tentative schema for the structural organization of these DAPA is proposed and shows a specific organization with local semi-crystalline segregation domains. DAPAe was found to possess the higher melting temperature likely due to higher crystal cohesion, which was confirmed by higher Young modulus in stress-strain experiments. Rheological data showed an increase of the glass transition temperature concomitantly with the increase of diamine chain length. They also revealed an increase of complex viscosity with the diamine chain length. Investigation of thermal stability showed that DAPAe degrades before DAPAh and DAPAo in connection with the number of methylene units per diamine.