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Influence of Chemical Structure and Molecular Weight on Fragility in Polymers

Kunal, Kumar
http://rave.ohiolink.edu/etdc/view?acc_num=akron1247855648

Abstract Details

2009, Doctor of Philosophy, University of Akron, Polymer Science.
Despite significant work in the field of glass transition, the effect of chemical structure of polymers on the glass transition and on the temperature variation of segmental relaxation times is not completely understood. The focus of this work is to study a wide range of synthetic polymers in order to understand how their chemical structures, molecular weights and intermolecular interactions affect ‘fragility’, a parameter used to quantify the temperature variation of segmental relaxation near the glass transition. The segmental dynamics were studied using dielectric spectroscopy and dynamic mechanical analysis. Polymers were chosen in a systematic way so that slight variations between their chemical structures would reveal the effect of particular structural parameters on Tg and fragility. Our analysis reveals that for polymers with weak Van der Waal’s interactions the flexibility of side groups relative to the flexibility of the backbone is the most important factor controlling fragility in polymers. On the other hand, glass transition temperature Tg primarily depends on the backbone flexibility and the side group bulkiness. Polymers are the least fragile when the side groups and backbone have the same stiffness. Fragility increases as the side groups become relatively stiff compared to the backbone or the backbone becomes relatively stiff compared to the sidegroups. Our model is consistent with the idea of the packing efficiency as the main parameter controlling fragility. Our study of the molecular weight dependence of fragility and Tg shows that the molecular weight dependence of fragility may not follow that of Tg, as earlier suggested. The most surprising result was found to be the decrease in fragility of poly(isobutylene) with increase in its molecular weight, despite an increase in its Tg. This result runs contrary to all theoretical predictions, and the reasons behind this unusual behavior are not completely understood. The study of polymers containing strongly polar chlorine and hydroxyl groups shows that the Tg of polar polymers is higher than that of non-polar polymers. However, there is no clear trend in change in fragility with increasing polarity.
Alexei Sokolov, Ph.D (Advisor)
163 p.
Polymers
Fragility; Glass Transition; Dielectric Spectroscopy; Dynamic Mechanical Analysis

Recommended Citations

Citations

  • Kunal, K. (2009). Influence of Chemical Structure and Molecular Weight on Fragility in Polymers [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1247855648

    APA Style (7th edition)

  • Kunal, Kumar. Influence of Chemical Structure and Molecular Weight on Fragility in Polymers. 2009. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1247855648.

    MLA Style (8th edition)

  • Kunal, Kumar. "Influence of Chemical Structure and Molecular Weight on Fragility in Polymers." Doctoral dissertation, University of Akron, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1247855648

    Chicago Manual of Style (17th edition)

akron1247855648
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© 2009, all rights reserved.
This open access ETD is published by University of Akron and OhioLINK.