Abstract: Melt flow rate was taken as a rough measure of molecular weight of isotactic polypropylene (IPP). Influence of molecular weight on the crystallization behavior, thermal property, and mechanical property of β-form IPP(β-PP) were studied using differential scanning calorimeter, X-ray diffraction, and mechanical property test. It was observed that after adding β-nucleating agent, both the crystallization temperature and heat distortion temperature of IPP increased about 10 ℃, relative content of β-form crystallization increased to 60 %~70 %. The impact strength of β-PP of high molecular weight increased at least 100 % while that of low molecular weight had little improvement. The flexural modulus and flexural strength of β-PP decreased compared with neat IPP, the lower the molecular weight, the more the decrease.

Key words: relative molecular weight, isotactic polypropylene, β-form, nucleating agent, melt flow rate