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Transesterification in blends of liquid crystalline copolyesters

McCullagh, Cindy Marie
http://rave.ohiolink.edu/etdc/view?acc_num=case1058534808

Abstract Details

1995, Doctor of Philosophy, Case Western Reserve University, Macromolecular Science.
The wholly aromatic copolymers of p-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) form nematic melts and maintain an extended chain structure upon solidification. The present work focuses on how this morphology influences physical and chemical changes that occur in blends of copolymers with different comonomer compositions. The X-ray diffraction data for these copolyesters contain non-periodic layer lines that indicate a completely random monomer sequence distribution and also provide analytical information on the monomer proportions. Hence these data provide a unique method to study transesterification between copolyesters of different composition. The melt transitions of the 75/25 and 30/70 copolymers occur at 288 and 303°C, respectively, but their 2:1 compatible blend has a much lower single melt transition at 227°C. This blend of the 75/25 and 30/70 copolymers initially shows the diffraction maxima characteristic of the two compounds, but transesterification occurs upon compression molding leading to the formation of the random copolymer of intermediate composition after one hour at 315°C. The progress of this reaction is followed by monitoring the positions of the first meridional maxima as a function of time, until they merge to give a single maximu m at the d-spacing characteristic of the random copolymer of intermediate composition. A progressive shift in the melt temperature from 227 to 248°C also indicates a gradual transition from a compatible blend to a random copolymer of intermediate composition during this time. Simulations of the diffraction effects are produced by incorporating terms into the correlation function to account for the changes in monomer nearest neighbor statistics that occur as transesterification progresses. The predicted scattering data are seen to follow the general trends of the observed data, and lead to the determination of an activation energy for the transesterification reaction that is comparable to values reported for isotropic polyesters. Finally, positron annihilation lifetime measurements indicate that the free volume of the unreacted blend is larger than those of the starting copolymers and the final transesterification product, which is consistent with the miscibility of these two copolyesters in the blend
John Blackwell (Advisor)
204 p.
Chemistry, Polymer
Transesterification; Liquid crystalline copolyesters

Recommended Citations

Citations

  • McCullagh, C. M. (1995). Transesterification in blends of liquid crystalline copolyesters [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1058534808

    APA Style (7th edition)

  • McCullagh, Cindy. Transesterification in blends of liquid crystalline copolyesters. 1995. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1058534808.

    MLA Style (8th edition)

  • McCullagh, Cindy. "Transesterification in blends of liquid crystalline copolyesters." Doctoral dissertation, Case Western Reserve University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=case1058534808

    Chicago Manual of Style (17th edition)

case1058534808
570
© 1995, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.