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X-ray analysis and molecular modeling of the structure of wholly aromatic copolyesters with thiophenyl or oxyphenyl side groups

Ishaq, Muhammad
http://rave.ohiolink.edu/etdc/view?acc_num=case1058446956

Abstract Details

1995, Doctor of Philosophy, Case Western Reserve University, Macromolecular Science.
The solid state structures of some wholly aromatic thermotropic copolyesters have been investigated by x-ray diffraction and molecular modeling techniques. The copolymers were prepared from p-hydroxybenzoic acid (HBA), biphenol (BP), hydroquinone (HQ) and terephthalic acid (TPA): in one copolymer the TPA was unsubstituted and in others, it was substituted with thiophenyl or oxyphenyl side groups (STPA or OTPA). The fiber diagrams of the unsubstituted copoly(TPA/BP/HBA) shows a series of sharp intensity maxima along the fiber axis direction and on layer lines. The meridional d-spacing are aperiodic suggesting that the copolymer chains have random monomer sequence and highly extended conformation. In chapter 2 we have analyzed the packing of non-identical sequences on the X-ray fiber diagrams of the BP series of substituted copolymers show a number of aperiodic intensity maxima along the fiber axis direction. The positions of these intensity maxima are similar to those for the unsubstituted system and have been reproduced by a method developed in this laboratory and applied to various copolymer systems. This method calculates the scattered intensity along the chain axis direction for a single aperiodic chain and averages over all possible sequences. A very good agreement between the calculated and observed data has been obtained for a structure consisting of chains with random monomer sequence and highly extended conformations. The effect of side groups on chain conformation has been analyzed by introducing different levels of non-linearity in the copolymer chains. The chains with substituents are about 1-2% more sinuous than those without X-ray data for the HQ series of substituted copolyesters contain periodic d-spacings along the fiber axis direction. This periodicity arises because the copolymer backbone has alternating phenylene and ester groups where the later may be COO or OCO experimentally observed lattice. Many arrays have been modeled to study different packing strategies. Using the molecular mechanics calculations, the potential energy of the starting arrays has been minimized by different methods. X-ray diffraction patterns have been simulated for the initial and optimized arrays. Almost all the observed Bragg reflections have been reproduced for the models in which chains were staggered along the chain axis to introduce registration between neighboring segments a nd then packed in herringbone fashion. Hence, an effective monomer repeat is observed. The calculated intensity maxima considering the random monomer sequence along the chain for these copolyesters is in excellent agreement with the observed data. Based on the results for the analogous BP series of substituted copolyesters. we believe that the HQ copolyesters also have random monomer sequence
John Blackwell (Advisor)
192 p.
Chemistry, Polymer
X-ray aromatic copolyesters; Thiophenyl, oxyphenyl side groups

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Citations

  • Ishaq, M. (1995). X-ray analysis and molecular modeling of the structure of wholly aromatic copolyesters with thiophenyl or oxyphenyl side groups [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1058446956

    APA Style (7th edition)

  • Ishaq, Muhammad. X-ray analysis and molecular modeling of the structure of wholly aromatic copolyesters with thiophenyl or oxyphenyl side groups. 1995. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1058446956.

    MLA Style (8th edition)

  • Ishaq, Muhammad. "X-ray analysis and molecular modeling of the structure of wholly aromatic copolyesters with thiophenyl or oxyphenyl side groups." Doctoral dissertation, Case Western Reserve University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=case1058446956

    Chicago Manual of Style (17th edition)

case1058446956
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© 1995, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.