Abstract
Summary: The crystal structures and possible transformations in poly(ethylene naphthalate) (PEN) were examined using differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD). The crystal cells (α‐ and β‐form) were dependent on several factors related to their thermal histories. For PEN subjected to T~max~ = 280 °C (where T~max~ is the maximum melt temperature at which the samples were treated before crystallization), only the α‐form developed regardless of the temperature of crystallization or cooling rate. However, for PEN subjected to T~max~ = 300 °C, PEN developed mixed dual crystals, with greater fractions of the α‐form at low temperatures of crystallization (220 °C or lower) or higher cooling rates, but higher β‐form fractions at higher crystallization temperatures (>230 °C). The difference in the relative stability of these two crystals was utilized to prepare PEN containing only the α‐form or only the β‐form. The equilibrium melting temperatures of these two crystal forms in PEN were then measured separately. For PEN containing only the β‐form, T (289.3 °C) was found by using the Hoffman‐Weeks technique, while for PEN containing only the α‐form, T was determined using the same technique but was found to be lower (282.6 °C).
Comparison of Hoffman‐Weeks extrapolations for the α‐crystal and β‐crystal, respectively, in PEN.
magnified imageComparison of Hoffman‐Weeks extrapolations for the α‐crystal and β‐crystal, respectively, in PEN.