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Understanding Molecular Epitaxial Mechanism and Chain Folding in Determining Chain Packing and Crystalline Morphology of Isotactic Polypropylene

Cao, Yan
http://rave.ohiolink.edu/etdc/view?acc_num=akron1335375714

Abstract Details

2012, Doctor of Philosophy, University of Akron, Polymer Science.
Although polymer crystal polymorphisms and their crystallographic relationships of isotactic polypropylene (i-PP) have been studied and understood for the past fifty years, we are still curious on some aspects of epitaxial mechanism between the alpha phase and the gamma phase. This research topic is designed to investigate how the epitaxial domination of the crystal morphologies takes place in the gamma-phase of the chain-folded crystals using high molecular weight isotactic polypropylene (i-PP) samples with a controlled number of stereodefects. Due to the specific epitaxial growth of the gamma-phase on the elongated alpha-phase single crystal, two different morphologies have been identified via transmission electron and atomic force microscopies (TEM and AFM). The epitaxial growth of the gamma-phase crystal is generated from the stem direction in the initial alpha-phase single crystal. The select area electron diffraction (SAED) results indicate that the chain orientations in the “flat” lamellae are tilted at ±40° from the thin film (lamellar) normal within the ab-plane of the gamma-phase. Based on the tilted SAED results from TEM, the microscopic formation mechanism of this morphology reveals that the initial alpha-phase single crystal has to have a stem orientation tilted 25 degree or 17 degree away from the thin film normal within the ac-plane around the b-axis. Elongated alpha2-form lath-like single crystals can be found by using both commercial sample and one with stereodefects. Based on our SAED experimental results, the stems in these lath-like single crystals are tilted at an unusual 17 degree angle around the b-axis. This 17 degree stem tilt in the alpha2-form single crystals with the (10-2) fold surface appears to depend upon both conformational and chain folding constraints.
Stephen Cheng, Dr. (Advisor)
Darrell Reneker, Dr. (Committee Chair)
Shiqing Wang, Dr. (Committee Member)
Toshikazu Miyoshi, Dr. (Committee Member)
Xiong Gong, Dr. (Committee Member)
95 p.
Polymers

Recommended Citations

Citations

  • Cao, Y. (2012). Understanding Molecular Epitaxial Mechanism and Chain Folding in Determining Chain Packing and Crystalline Morphology of Isotactic Polypropylene [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1335375714

    APA Style (7th edition)

  • Cao, Yan. Understanding Molecular Epitaxial Mechanism and Chain Folding in Determining Chain Packing and Crystalline Morphology of Isotactic Polypropylene. 2012. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1335375714.

    MLA Style (8th edition)

  • Cao, Yan. "Understanding Molecular Epitaxial Mechanism and Chain Folding in Determining Chain Packing and Crystalline Morphology of Isotactic Polypropylene." Doctoral dissertation, University of Akron, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1335375714

    Chicago Manual of Style (17th edition)

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© 2012, all rights reserved.
This open access ETD is published by University of Akron and OhioLINK.