Mesophase-Mediated Crystallization of Poly(butylene-2,6-naphthalate): An Example of Ostwald's Rule of Stages.

The investigation of poly(butylene-2,6-naphthalate) crystallization by means of chip-calorimetry and ultrafast wide-angle X-ray diffraction (WAXD) revealed the existence of two possible mechanisms. The formation of the stable triclinic α-phase occurs directly from the undercooled melt at low cooling rates/high crystallization temperature. At higher cooling rates a two-stage route is observed: crystallization is preceded by the formation of a mesomorphic phase from the isotropic melt. The monotropic behavior of poly(butylene-2,6-naphthalate), becoming apparent only under severe cooling conditions, obeys the well-known Ostwald's rule of stages.