Doctoral Dissertations

Date of Award

8-2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Mark D. Dadmun

Committee Members

Jimmy W. Mays, Robert J. Hinde, Joseph J. Bozell

Abstract

This dissertation addresses three aspects of multi-component polymer systems. Chapter 2 details work on understanding the effect of precise polymeric structure on the phase behavior of blends containing cellulose acetate chains with different levels of acetate substitution. The difference in degree substitution (Delta DS) between the two components in the blend is systematically changed from .06 to .63, where each blend is found to be partially miscible. The samples containing higher acetate content demonstrate decreased miscibility as Delta DS increases. The sample with the most hydroxyl groups, however, has greater miscibility than samples of similar Delta DS, but fewer hydroxyl groups, indicating that hydroxyl groups promote mixing through favorable hydrogen bonding between blend components, highlighting the significant impact that specific interactions have on the miscibility of cellulose acetate blends.

The effect of non-bonding interactions is further investigated in Chapter 3, detailing the impact of thermodynamic interactions on the dynamics of a series of homopolymer/copolymer blends of 90% poly(methyl methacrylate) and 10% poly(methyl methacrylate)-co-poly(styrene). The copolymer composition varies from 60% to 90% MMA, effectively tuning the blend’s thermodynamic interactions. The analysis indicates that the thermodynamic interactions in the system significantly impact copolymer dynamics. Comparison to the Lodge-McLeish model indicates that the local environment around the copolymer is richer in styrene than the model predicts. These homopolymer/copolymer blends indicate that the local composition and dynamics are significantly impacted by the repulsive interactions between styrene and methyl methacrylate. These results emphasize the importance of thermodynamic interactions on the dynamics of miscible homopolymer/copolymer blends.

Chapter 4 further explores structure-property relationships of multi-component polymer systems utilizing neat polystyrene (PS)-polyisoprene (PI) block copolymers. The volume fraction of PS, PI, and molecular weight are held constant, varying the connectivity of the components from a linear PS-PI diblock copolymer to three different miktoarm star architectures: PS2-PI, PS-PI2, and PS2-PI2. The investigation indicates a change in morphological features due to excluded volume effects at the junction point of the star. Experimentally observed morphologies for different chain architectures are generally consistent with self-consistent field theory simulations, and agree with analytical theory predictions that account for architectural and conformational asymmetry.

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