Melt-crystallization of poly(butylene 2,6-naphthalate) (PBN) at temperatures lower than about 160 degrees C follows Ostwald's rule of stages via intermediate formation of a smectic liquid crystalline phase (LC-phase). The transient LC-phase has been isolated by interruption of the isothermal crystallization process at 140 degrees C at sub-second timescale, and then its disordering was analyzed on heating at a rate of 2000 K/s, which suppresses the transition into a-crystals. The disordering temperature of the LC-mesophase is slightly lower than 200 degrees C, and as such 20-30 K lower than the melting temperature of alpha-crystals formed from the LC-phase at 140 degrees C. Analysis of the bulk enthalpy of formation of the LC-phase revealed that it covers only 20-25% of the total bulk enthalpy of crystallization, which is considered further proof of its smectic nature.