Structural change in the Brill transition of Nylon m/n (2) conformational disordering as viewed from the temperature-dependent infrared spectral measurements

The structural changes in the Brill transition of aliphatic Nylons m/n have been investigated by carrying out the temperature-dependent infrared spectral measurement for Nylon 6/10 –[–NH–(CH2)6–NHCO–(CH2)8–CO–]n–, Nylon 6/12 –[–NH–(CH2)6–NHCO–(CH2)10–CO–]n– and Nylon 10/10 –[–NH–(CH2)10–NHCO–(CH2)8–CO–]n–. They took the crystal structure of α-form at room temperature. By heating the samples up to the Brill transition temperature region, the conformation of the methylene segments was found to change remarkably from the all trans-zigzag form to the disordered conformation constructed by shorter trans-zigzag segments combined with some gauche bonds. At the same time, the twisting motion was found to occur around the CH2–amide bonds. During this order-to-disorder transition of molecular conformation, the intermolecular hydrogen bonds were kept alive although they were weaker gradually with increasing temperature. The methylene segments sandwiched by NH groups [NH(CH2)mNH] were found to be disordered more remarkably than those of CO(CH2)nCO sequence due to the difference in torsional energy barriers around the CH2–NH and CH2–CO bonds.