Melting and spherulitic crystallization of a phenyl benzoate

Abstract

Melting and solidification of BPC (butyl p-(p-ethoxyphenoxy-carbonyl)phenylcarbonate) have been studied by polarization microscopy and differential scanning calorimetry. BPC can exist at room temperature in two different crystallographic modifications which melt directly into the nematic state at different temperatures (c. 330·5 K and 338·5 K). The nematic fluid crystallizes below c. 313 K to form simultaneously two types of spherulitic aggregates corresponding to the two crystal types. Both the spherulites possess a positive birefringence; but they vary significantly in their morphological and kinetic aspects. Further, in one of them the molecular long axes are radial, while in the other they are tangential. This fact emerges from optical and electrooptical observations on the pseudomorphic nematic domains obtained by melting the spherulites. Above 313 K, the crystals that grow are nonspherulitic, lamellar, biaxial and optically positive; they melt at c. 338·5 K. The glassy nematic state is realised by rapidly quenching the melt to a low temperature (100 K). On heating, the glassy state transforms into the supercooled nematic state near 234·5 K.