Bio-based polyamide 11: synthesis, rheology and solid-state properties of star structures

Polyamide 11 (PA11) is a bio-based technopolymer synthesized using 11-aminoundecanoic acid from castor oil. In this work star-shaped PA11 structures are obtained via one-pot copolycondensation of 11-aminoundecanoic acid with a multifunctional agent, either 3-functional bis hexamethylentriamine or tetra-functional 2,2,6,6-tetra[β-carboxyethylcyclohexanone]. A theoretical model predicting the macromolecular complexity of the star shaped polycondensates that result from the reaction is used to interpret the rheological behavior of the synthesized samples, that is found to be strongly affected by the presence of branching. It is shown that melt properties can be modulated, for easier processability, by simply controlling monomer feed ratio and conversion of the copolycondensation reaction. In the range of comonomer functionality and content explored, thermal properties do not significantly vary with changing macromolecular architecture. All star-shaped polyamide samples easily crystallize and their structural characterization above room temperature shows that upon heating they reversibly undergo the alpha-gamma crystal phase transition that is typical of linear PA11. Investigation of the effect of branching on the mechanical properties shows that careful selection of chain controller type and amount allows to obtain star-shaped PA11 samples with ad-hoc modulated melt viscosity and preserved material’s mechanical performance.