This dissertation presents a discussion of blocky and randomly functionalized sulfonated syndiotactic polystyrene copolymers. These copolymers have been prepared over a range of functionalization (from 2% to 10%) in order to assess the effect of the incorporation of these polar side groups on both the thermal behavior and morphology of these polymer systems. The two different architectures are achieved by conducting the reaction in both the heterogeneous gel-state to obtain blocky copolymers and in the homogeneous solution state to obtain randomly functionalized copolymers. In order to compare both the thermal properties and morphology of these two systems several sets of samples were prepared at comparable levels of sulfonation. Thermal analysis of these two systems proved that the blocky functionalized copolymers provided superior properties with regard to the speed and total amount of the crystalline component of sulfonated syndiotactic polystyrene. Above 3% functionalizion the randomly functionalized copolymer was no longer able to crystallize, whereas, the blocky functionalized copolymer is able to crystallize even at a functionalization level of 10.5% sulfonate groups. When considering the morphology of these systems even at low percentages of sulfonation it is clear that the distribution of these groups is different based on the amplitude of the signal measured by small angle x-ray scattering. Additionally, methods were developed to describe both the distribution of ionic multiplets, which varies between blocky and randomly functionalized systems, but also the distribution of crystals. At a larger scale ultra-small angle x-ray scattering was employed to attempt to understand the clustering of ionic multiplets in these systems. Randomly functionalized polymers should a peak that is attributed to ion clusters, whereas blocky polymers show no such peak. Additional studies have also been done to look at the analysis of crystallite sizes in these systems when there are multiplet polymorphs present, it was observed the polymorphic composition is drastically different. All of these studies support that these systems bear vastly different thermal behavior and possess significantly different morphologies. This supports the hypothesis that this gel-state heterogeneous functionalization procedure produces a much different chain architecture compared to homogeneous functionalization in the solution-state. / Doctor of Philosophy / Polymers are a class of chemicals that are defined by having a very large set of molecules that are chemically linked together where each unit (monomer) is repeated within the chemical structure. In particular, this dissertation focuses on the construction what are termed as "blocky" copolymers, which are defined by having two chemically different monomers that are incorporated in the polymer chain. The "blocky" characteristic of these polymers means that these two different monomers are physically segregated from each other on the polymer chain, where long portions of the chain that are of one type, followed by another section of the polymer that has the other type of monomer. The goal of creating this type of structure is to try to take advantage of the properties of both types of monomers, which can create materials with superior synergistic properties. In this case a hydrophobic (water hating) monomer is combined with a hydrophilic (water loving) chain. This hydrophobic component in the polymer is able to crystallize, which provides mechanical and thermal stability in the material by acting as a physical tether to hold neighboring chains together. With the other set of hydrophilic monomers, which in this case have an ionic component incorporated, we can now take advantage of this chemical components ability to aide in the transportation of ions. Transportation of ions is useful in a variety of commercially relevant applications, two of the most important applications of these ionic materials is in membranes that can be used to purify water or membrane materials in fuel cell technologies, specifically for proton exchange membranes. The focus of this research in particular was to create a simple synthesis technique that can create these blocky polymer chain architectures, which is done by performing the reaction while the polymer is made into a gel. The key to this is that the crystals within the gel act as a barrier to chemical reactions, creating conditions where we have substantial portions of the material that are able to be functionalized and the crystals within the material that are protected from being functionalized. By looking at the thermal characteristics, such as melting temperatures and amount of crystals within these systems we have seen that functionalizing these polymers in the heterogeneous gel state gives substantially better properties than functionalizing these materials randomly. Much like oil and water, incompatible polymer chains will phase separate from each other. In this case the hydrophobic and ionic components will phase separate from each other. The shape and distribution of these phase separated structure will dictate many of the material properties, which can be described by modeling the data collected from x-ray scattering experiments. All of this information will tell us based on the initial conditions that these polymers were created in, what properties should be expected based on the morphology and thermal behavior. This gives a better understanding of how to fine tune these properties based on the structure of the gel and chemical reaction conditions.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/97193 |
| Date | 04 March 2020 |
| Creators | Fahs, Gregory Bain |
| Contributors | Chemistry, Moore, Robert Bowen, Long, Timothy E., Cheng, Shengfeng, Liu, Guoliang |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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