“…Since the degradation of synthetic polymers in marine environments is based on a hydrolysis reaction, it is crucially important to obtain a better understanding of not only the activities of the specific microorganisms but also the change in the aggregation states and thermal molecular motion of the polymers under aqueous conditions . In general, various polymers have been known to change their aggregation states − and dynamics − even in contact with a non-solvent, leading to a marked change in functions. − Also, it has been reported that the addition of hydrophilic components into polymers to increase the water content promotes the degradation of polymers. − From these perspectives, polyamide 4, hereafter referred to as PA4, which has four carbon atoms between neighboring amide bonds, is considered to be a promising degradable polymer in the family of polyamides. − PA4 can absorb more water molecules due to the higher number density of hydrophilic amide bonds and results in good biodegradability even in normal marine environments. , Furthermore, 2-pyrrolidone, which is the monomer for PA4 upon ring-opening polymerization, can be produced from l -glutamic acid via bioprocesses, and PA4-specific enzymes have also been isolated. , Based on these facts, it is expected that PA4 will be available for use as a fully bio-based degradable polymer in the near future. Nevertheless, many of the detailed studies for aggregation states and physical properties, in aqueous conditions especially, have focused on commercially available PA6 − rather than PA4.…”