Phase Transitions in Nylon Crystals with Hexamethylene Moiety

抄録

The temperature dependence of crystal structure and specific heat is measured at normal pressure and/or high pressures for nylons with a hexamethylene moiety (nylons 62, 66, 68, 48 and 7). First-order phase transition occurs in the as-synthesized nylon 62 crystal at normal pressure. First- and second-order phase transitions are observed in the solution-crystallized nylon 68 crystal under elevated pressures similarly to nylon 66, and while the structural change of nylon 48 and 7 crystals is gradual, no phase-transitional phenomena are observed. Such results suggest that the hexamethylene moiety between NH groups plays an intrinsic role in phase transition, and that the moiety between CO groups does not seem to contribute to the phase-transitional aspect in nylon crystals due to rotational hindrance around the (CO)-C bond.