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Elucidation of Chain-Folding Structure and Crystallization Mechanism of Semicrystalline Polymer by Solid-State NMR

Hong, Youlee
http://orcid.org/0000-0003-3141-5818
http://rave.ohiolink.edu/etdc/view?acc_num=akron1430246993

Abstract Details

2015, Doctor of Philosophy, University of Akron, Polymer Science.
Since Keller found single crystal of polyethylene (PE) in 1957, he first proposed the long polymer chains are more or less regularly folded in thin lamellae and the chain stems between successive folds oriented preferentially normal to the plane of the lamellae. The discovery has triggered the study of how long polymer molecules are embedded in the thin lamellae of semicrystalline polymers. Subsequently, several different crystallization mechanisms had been proposed such as Lauritzen-Hoffman kinetic theory, multistage model, aggregation model, and bundle model, etc. In order to prove these crystallization models, chain trajectory of semicrystalline polymers have been investigated prominently by neutron scattering (NS) and infrared (IR) spectroscopy combined with 1H/2H polymers because the chain-level structure would reflect the process during the crystallization. Later on, other techniques such as atomic force microscopy (AFM) and decoration method on the surface of PE crystals have been developed. Irrespective of the tremendous efforts over the last half century, the detailed chain trajectory of semicrystalline polymers still remains missing due to insufficient resolution of available techniques and intrinsic polymer structures that consist of repeating monomer units. Therefore, various crystallization theories could not be verified until now and hence a new approach is required to clarify the molecular level structure. In this dissertation, we have developed a novel strategy to investigate chain trajectory of semicrystalline polymers as a function of concentration and crystallization temperature. We have used solid-state nuclear magnetic resonance (SS-NMR) spectroscopy combined with selectively 13C isotopic labeling approach. Since the SS-NMR approach based on 13C-13C magnetically dipolar interactions has atomic level resolutions, the approach was able to investigate the chain trajectory of isotactic poly(1-butene) (iPB1). 13C-13C double quantum (DQ) NMR and spin-dynamics simulations determined adjacent re-entry parameters of the re-entrance site, chain-folding fraction (F), average successive chain-folding number <n>, and molecular dimension of folded chains of iPB1 with a relatively low Mw of 37 K g/mol in melt- and solution-grown crystals in a wide range of crystallization temperature (Tc). The determined chain trajectory of form I iPB1, which is one of the type of iPB1 crystal form, turned out that the re-entrance site of iPB1 is independence of the concentration and crystallization temperatures while the lower concentration induces long-range order and higher fraction of adjacent re-entry chain-folding. The <n> and F values were nearly invariant of Tc in each the solution- and melt-grown systems. In addition, we studied the effects of Tc on the lamellar thickness (<lc>), crystallinity (xc), and morphology of iPB1 crystallized in both states. The combined data obtained at different length scales demonstrated that kinetics plays different roles for the structural formations from molecular to morphological levels. Lastly, another iPB1 form III displayed three dimensional clusters of folded chains instead of the two dimensional one expected by classical surface nucleation model of crystallization. Through the molecular level structures, xc, <lc>, morphology of single crystal, and the dimension of folded chains as well as the molecular dynamics information reported in the literature, we discussed the crystallization mechanisms of semicrystalline polymer from a molecular level of view.
Toshikazu Miyoshi, Dr. (Advisor)
Ali Dhinojwala, Dr. (Committee Member)
Darrell H. Reneker, Dr. (Committee Member)
Mesfin Tsige, Dr. (Committee Member)
Thein Kyu, Dr. (Committee Member)
207 p.
Polymers
polymer crystallization, solid-state NMR

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Citations

  • Hong, Y. (2015). Elucidation of Chain-Folding Structure and Crystallization Mechanism of Semicrystalline Polymer by Solid-State NMR [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1430246993

    APA Style (7th edition)

  • Hong, Youlee. Elucidation of Chain-Folding Structure and Crystallization Mechanism of Semicrystalline Polymer by Solid-State NMR . 2015. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1430246993.

    MLA Style (8th edition)

  • Hong, Youlee. "Elucidation of Chain-Folding Structure and Crystallization Mechanism of Semicrystalline Polymer by Solid-State NMR ." Doctoral dissertation, University of Akron, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1430246993

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Akron and OhioLINK.