Effects of ultrasound on the conformational and crystallization behavior of isotactic polypropylene polymerized with different Ziegler—Natta catalyst

Abstract

Using different Ziegler—Natta catalysts, we have prepared two samples of isotactic polypropylene with similar molecular weight and average isotacticity, but different stereo-defect distributions. The influence of ultrasonic irradiation on the conformation and crystallization behavior of those samples were investigated by differential scanning calorimetry, wide-angle X-ray diffraction and Fourier transform infrared spectroscopy. The ultrasonic treatment induced a decrease in the degree of crystalline perfection and a wider distribution range of the crystalline perfection of polypropylene. Meanwhile, the crystal particles pack looser and the crystallite size decreased under the influence of ultrasonic irradiation. On the conformation aspect, the molecular movement in polypropylene became more intensive, the molecular entanglement was reduced when ultrasound was applied. Moreover, it was found that the uniformity of stereo-defect distribution also played important role in determining the conformation and crystallization behavior of polypropylene samples irradiated by ultrasound.