Dissolution of hydrogen bonded polymers in water; from synthetic to biopolymers

In several nylons, for example nylon 4,6, a transition occurs at elevated temperatures in which the hydrogen bonding between adjacent chains is most likely to weaken, the so-called Brill transition. In this communication the influence of superheated water on nylon 4,6 at and above the Brill transition temperature is investigated, superheating being achieved by increased vapour pressure upon heating water and nylon in a sealed glass capillary. From time-resolved X-ray studies it is shown that close to the Brill transition temperature, nylon 4,6 dissolves in water. Crystallization from the solution still under moderate pressures (∼20bars) leads to the formation of single crystals. These crystals grow directly in the triclinic phase without the intervention of the pseudo-hexagonal phase. By Infrared spectroscopy we speculate that water intercalated within the confined geometry of the unit cell leads to a unique vibrational spectra. The trapped water exits from the unit cell above the Brill transition temperature, once the vapour pressure is released. These experimental findings are not limited to a specific polymer, but have implications for the dissolution of all hydrogen bonded polymers, irrespective of whether they are synthetic or biopolymers.