Microscopic Fourier Transform Infrared Characterization on Two Types of Spherulite with Polymorphic Crystals in Poly(heptamethylene terephthalate)

FTIR microspectrometry with in situ temperature variation and IR-peak-mapping capability, and POM characterization were used to study the crystal distribution in dual spherulites in poly(heptamethylene terephthalate). By tracing the crystalline IR bands of the α-crystal and β-crystal to get the crystal distribution, the techniques resolve that the ringed and ringless spherulites comprise α- and β-crystals, respectively. In addition, temperature-dependent IR analyses on the spots related to the two crystals also reveal the α- and β-crystals melt at 98 and 104 °C, respectively. The ringed and ringless spherulites were proven to be correlated with the α- and β-crystal forms, respectively.