The effect of molecular mass on the polymorphism and crystalline structure of isotactic polypropylene

Abstract

This study is devoted to the investigation of the effect of molecular mass on the α-, β- and γ-crystallization ten- dency of isotactic polypropylene (iPP). The crystalline structure was studied by wide angle X-ray scattering (WAXS) and by polarised light microscopy (PLM). The melting and crystallization characteristics were determined by differential scan- ning calorimetry (DSC). The results indicate clearly that iPP with low molecular mass crystallizes essentially in α-modifi- cation. However, it crystallizes in β-form in the presence of a highly efficient and selective β-nucleating agent. The α- and β-modifications form in wide molecular mass range. The decreasing molecular mass results in increased structural instabil- ity in both α- and β-modifications and consequently enhanced inclination to recrystallization during heating. The formation of γ-modification could not be observed, although some literature sources report that γ-form develops in iPP with low molecular mass.