Date of Award

5-2017

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Chemistry

Committee Member

Dr. Dvora Perahia, Committee Chair

Committee Member

Dr. Stephen Creager

Committee Member

Dr. Rhett Smith

Abstract

This work focuses on the association of a structured multifunctional co-polymer in solutions and thin films as studied using neutron techniques and atomic force microscopy. Tethering multiple blocks into structured architectures is a promising way to tailor block copolymers with well-defined properties. Polymer films are often cast from solutions. Therefore, understanding the association of complex polymers in solutions and the impact of the aggregates into thin films is crucial to design materials with well-defined properties. Ionically-decorated blocks facilitate transport of ions and response to electrical fields. However they also affect the polymer structure. This work is divided into two sections. The first one resolves aggregation of a symmetric van der Waals pentablock polymer in solutions. The second follows film structure as charged groups are introduced. Specifically, we probed the assembly of polymers having an A-B-C-B-A co-polymer architecture, where co-polymer C is polystyrene, B is hydrogenated poly (ethylene-r-propylene) and A is poly (t-butyl styrene). In solutions we studied non-ionic pentablock polymers and in thin films we studied ionic pentablock polymers. In the solution study, the solvent polarity was tuned by controlling the ratio of cyclohexane to propanol. We find that, in contrast to most block copolymers, this pentablock polymer associates into fractal aggregates in cyclohexane which become more self-similar with increasing temperature. Increasing solvent polarity, by addition of propanol, drives the collapse of pentablock chains which leads the formation of more spherical aggregates. The structured architecture of the pentablock polymer enhances entropy resulting in less well-defined shapes that are maintained over a broad temperature range. In thin films, we probed the ionic analog of the above co-polymer where C is a randomly sulfonated polystyrene with sulfonation fractions of 0, 26 and 52 mole %, as the sulfonation level and thermal annealing times are varied using atomic force microscopy, surface tension measurements and neutron reflectivity. Our results show that as cast films form layers with both hydrophobic blocks dominating the solid and air interfaces and the ionizable block segregates to the center. With annealing at 170°C, above Tg of styrene sulfonate, the films coarsen, with surface aggregation dominating the structure, though interfacial regions remain dominated by the hydrophobic segments.

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