Comparison of the crystallization behavior at high cooling rates of isotactic polypropylene resins with differing tacticity and comonomer content

The quiescent crystallization behavior of six polypropylene resins varying in tacticity and ethylene content were investigated by light depolarization microscopy (LDM) and differential scanning calorimetry (DSC). The overall transformation kinetics were found to be strongly dependent on three parameters: tacticity, comonomer content, and the presence of adventitious nuclei. The latter quantity controls nucleation density and affects the temperature at which crystallization occurs and the final spherulite size. The alpha-phase was found to be the primary crystalline form present at cooling rates up to 4000 degrees C per minute.