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Study of Polystyrene and Acrylonitrile−Styrene Copolymer as Special β-Nucleating Agents To Induce the Crystallization of Isotactic Polypropylene

2007; American Chemical Society; Volume: 40; Issue: 12 Linguagem: Inglês

10.1021/ma0623587

1520-5835

Zhiqiang Su, Mu Dong, Zhao‐Xia Guo, Jian Yu,

biodegradable polymer synthesis and properties

The influence of two kinds of polymers (polystyrene (PS), acrylonitrile−styrene copolymer (SAN)) on the crystallization behavior of isotactic polypropylene (iPP) has been investigated by means of wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and polarized optical microscopy (POM). The current experimental results indicated that these two kinds of polymers with low concentration, as special β-nucleating agents, can induce the β-iPP polymorph during quiescent melt crystallization. The nucleating activity of SAN or PS significantly depends on its concentration, molecular structure, and thermal history of processing. The content of β-crystal form increases with the increasing crystallization temperature or nucleating agent (SAN or PS) percentage, reaches a maximum value, and then decreases as the temperature or nucleating agent percentage further increases. Under the same crystallization condition, SAN is more effective than PS on inducing a higher level of β-crystal form in iPP. Besides, variable temperature WAXD and POM experiments have been used to investigate the polymorphism and the crystalline phase transformation of iPP. It was proved that the β-crystal form of iPP is a thermodynamically metastable structure and will gradually transform to a new kind of α'-crystal form with the rise in crystallization temperature. Because of different structural characteristics, the polymeric nucleating agents exhibit nucleation and crystallization mechanism which differ from the traditional low molecular weight β-nucleating agents of iPP.