Influence of thermal history on primary nucleation and crystal growth rates of isotactic polystyrene

The influence of thermal history on primary nucleation and crystal growth rate of isotactic polystyrene (i-PS) was studied in a wide range of time and temperature. Samples were melted at several temperatures from 230 to 250 °C and then crystallized from those molten states and also crystallized from the glassy state. The primary nucleation rate is strongly influenced by the thermal history but the crystal growth rate is mainly governed by the crystallization temperature. Below a melt temperature of 230 °C, the nucleation density was attributed to the seed nuclei, which result from incomplete melting of the spherulites. Above 250 °C, a limited number of heterogeneous nucleation sites remain, and these sites are activated on the surface of impurities or foreign bodies in the melt. The primary nucleation is controlled heterogeneously both from the molten and the glassy states. The nucleation rate from the glassy state is faster than that from the molten state. A linear relationship between the nucleation rate and the inverse of induction time was found in each experimental condition and their slopes are related to the saturation density of the nuclei. The activation energy for the molecular transport and the primary nucleation energy were smaller than those of the crystal growth. The primary nucleation energy from the glass was lower than that from the melt. These energies are discussed in the present work.