Comonomers modulating the strength of hydrogen bonding were introduced in polyamide 66 (formation of PA66/6HIA copolymers), and entailed an increase of fatigue life-time at low stress by one half decade. In addition, a block copolymer structure was targeted and obtained by reactive extrusion, in order to not hinder PA66 crystallization.
At the end we showed that fine-tuning intermolecular interactions influence fatigue lifetime at least as much as other microstructural parameters such as crystallinity (crystalline fraction and crystalline perfection) and molecular weight (PhD Naji Hussein 2009-2012). 2 patents were filed in 2012 and 2013.
Physical mechanisms of fatigue in neat polyamide, E. Mourglia-Seignobos, D. R. Long, L. Odoni, L. Vanel, P. Sotta, C. Rochas, Macromolecules 2014, 47, 3880-3894.