1ST-ORDER PHASE-TRANSITION IN A NYLON-66 CRYSTAL

Electron diffraction patterns and specific heat at constant pressure (C(p)) are recorded in a temperature range between approximately 300 K and 500 K for a nylon 66 crystal precipitated at 418 K from 0.05-wt% 1,4-butanediol solution. The C(p) is found to take a maximum value at 468 K (T(t)) under 0.1 MPa (atmospheric pressure). Three reflections of 100, 010 and 110 can be observed independently in an electron diffraction pattern, all of which show symmetrical single-peak profiles at temperatures lower than T(t), while 010 and 110 profiles are found to be asymmetric or to have shoulders in the smaller-diffraction-angle region at T(t). These results give the first evidence that two crystalline phases coexist or that first-order phase transition occurs at T(t) in the nylon 66 crystal.