Abstract: A comparative investigation was conducted on three types of copolymerized polypropylene (K8303, K8003 and EPS-30R) with a low melt flow rate. The relationship of structure and performance was evaluated by means of mechanical measurement and NMR characterizations, and the crystal morphology and phase structure were observed by polarizing microscope and scanning electron microscope, respectively. The results indicated that the spherulite size and the content of rubber phase influenced the balance between the stiffness and impact toughness significantly. The spherulite sizes of K8303 and K8003 are smaller than those of EPS-30R due to their higher content of rubber phase, and thus they exhibited much higher impact toughness.

Key words: copolymerized polypropylene, ethylene-propylene rubber, spherulite size, rubber phase, impact toughness