Structure-property behavior of poly(ethylene oxide) based poly(urethane-urea) copolymers and their nanocomposites reinforced by silica nanoparticles
Oğuz, Oğuzhan (2017) Structure-property behavior of poly(ethylene oxide) based poly(urethane-urea) copolymers and their nanocomposites reinforced by silica nanoparticles. [Thesis]
Structure-property relationships of poly(ethylene oxide) (PEO) based poly(urethane-urea) (PU) copolymers and PU-silica nanocomposites form the basis of this thesis work. On this basis, a brief introduction is provided in Chapter 1. In Chapter 2, the effects of PEO soft segment molecular weight (2000, 4600 and 8000 g/mol) and annealing temperature (60 and 100 °C) on the development of polymer morphology and mechanical properties are investigated. Results strongly suggest that both parameters have significant effect on the final morphologies and mechanical properties of the copolymers. In Chapter 3, the effect of PEO soft segment molecular weight on the glass transition, crystallinity, molecular mobility, and segmental dynamics of these copolymers is investigated using modulated differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS). Results mainly suggest that the soft segment molecular weight also significantly affects the thermal properties and five different relaxation mechanisms of the copolymers. In Chapter 4, structure-property behavior of PU-silica nanocomposites is investigated using several characterization techniques. In particular, thermal and mechanical properties of the samples are evaluated as a function of silica content. Results clearly suggest that the silica nanoparticles significantly tailor the thermal and mechanical properties of the nanocomposites in conjunction with the effect of soft segment molecular weight. In Chapter 5, the dynamic glass transition of the rigid amorphous fraction in PU-silica nanocomposites is demonstrated by several advanced characterization techniques. Results mainly suggest a plausible explanation for the discrepancy between Tg values obtained by dielectric relaxation spectroscopy and differential scanning calorimetry in the literature. It is that DRS results in Tg values taking into account the bound polymer, whereas DSC does not. In Chapter 6, key design principles are summarized to provide a practical guideline for the production of high performance PU copolymers and PU-silica nanocomposites, and a better understanding of their structure-property relationships in accordance with the elaborated investigations presented in Chapter 2, 3, 4 and 5.
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