Isothermal crystallization behavior of metallocene-catalyzed isotactic polypropylene

다국어 초록 (Multilingual Abstract)

<P>Isothermal crystallization behavior of isotactic polypropylene (iPP) synthesized using metallocene catalyst was investigated in this work. The isotacticity of the polypropylene was characterized by <SUP>13</SUP>C-NMR spectroscopy. It was found that the melting temperature (T<SUB>m</SUB>) of the iPP is 123.51°C and the crystallization temperature (T<SUB>c</SUB>) is 93°C. The iPP synthesized in this work did not show a general increase of T<SUB>m</SUB> with an increase of crystallization temperature T<SUB>c</SUB>, 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 (ΔH<SUB>f</SUB>) with decreasing crystallization temperature. All the spherulites of iPP samples showed negative birefringence. For the iPP sample crystallized at the highest T<SUB>c</SUB> (= 123°C, just below T<SUB>m</SUB>), 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. J Appl Polym Sci 95: 231–237, 2005</P>