Isothermal crystallization behavior of metallocene-catalyzed isotactic polypropylene

Abstract

Isothermal crystallization behavior of isotactic polypropylene (iPP) synthesized using metallocene catalyst was investigated in this work. The isotacticity of the polypropylene was characterized by 13C-NMR spectroscopy. It was found that the melting temperature (Tm) of the iPP is 123.51°C and the crystallization temperature (Te) is 93°C. The iPP synthesized in this work did not show a general increase of Tm with an increase of crystallization temperature T c′, due to the short crystallization time of 20 min and low molecular weight (number average molecular weight = 6,300). The iPP showed a tendency of increasing heat of fusion (ΔHf) with decreasing crystallization temper ature. All the spherulites of iPP samples showed negative birefringence. For the iPP sample crystallized at the highest T c (= 123°C, just below Tm), the spherulite showed a pronounced Maltese Cross and a continuous sheaf-like texture aligning radially, which suggests that R-lamellaes are dominant in this spherulite. The crystalline structure of the iPP was also investigated by X-ray diffraction. © 2004 Wiley Periodicals, Inc.