New observations on the formation of "row-nucleated" structures of isotactic polystyrene

A unique 60 degrees C endothermic peak was found in the differential scanning calorimetry (DSC) measurement of freeze-dried isotactic polystyrene (i-PS) prepared from a 0.01 wt % benzene solution. While i-PS was melted before preparing a solution at a temperature beyond the equilibrium melting point, nothing could be observed around 60 degrees C. The endotherm can be attributed to the melting of microgel crystals. Morphology observation revealed that ribbonlike films of i-PS were formed when the solution was spread on a cold water surface. After isothermal crystallization of the films, "row-nucleated" crystals were grossly produced without any extensional deformation of molecular chains. It is suggested that microgel crystals may act as heterogeneous species to initiate the growth of "row-nucleated" crystals.