Date of Award
Doctor of Philosophy (PhD)
Rhett C. Smith
Stephen E. Creager
Daniel C. Whitehead
In Chapter 1, recent advances in thermally stable polymers and polyectrolytes are reviewed, with an emphasis on elucidating the extent to which structural variations influence thermal stability. Specific polymers such as polybenzimidazoles, polyimides and phosphonium polyelectrolytes (PELs) were selected to illustrate how properties can be tuned through modification of side chain, main chain and functional group composition. Recent development on PPELs are a particular emphasis in this chapter, and this serves as an introduction to the state-of-the-art prior to work conducted in the current dissertation.
The work presented in Chapters 2 and 3 is centered on structure-property relationship studies employing PELs that were prepared via condensation polymerization. The properties of PELs were evaluated in an effort to assess the influence of both side chain and main chain composition. The influence of side chain was examined by comparing properties of a series of PELs having hydrophobic octyloxy side chains to those of structural analogues lacking the side chains. The influence exerted by backbone flexibility/length of spacer between charges was revealed by comparing properties of two series of polymers with a variable number of methylene units between phosphonium charge-bearing sites. Side chain composition and spacing between phosphonium units lead to noteworthy influence on thermal stability, glass transition and crystallinity. The molecular structure of PELs also correlates with trends in film morphology and critical surface energy of PEL dip-cast films. Sensitivity of morphology to humidity or water in the casting solvent was observed. The relationship between side chain and spacer on bactericidal activity against Staphylococcus aureus and Escherichia coli was assessed. Supramolecular assembly of films via layer-by-layer deposition of PELs alternating with anionic polythiophene derivative layers was also undertaken. The linearity of film growth, amount of material deposited in each bilayer, polycation:polyanion ratio and film roughness all show noteworthy trends that depend on both the presence/absence of side chains and on spacing between ionic centers.
Chapters 4 and 5 detail work on a series of phosphonium-containing covalent organic frameworks (COFs) (P1-P4) prepared via copolymerization of 1,4-diacetylbenze and bis(4-acetylphenyl)diphenylphosphonium bromide in various ratios. The influence of COF composition on thermal stability, alkaline stability, char yield, water uptake, specific surface area, and CO2 affinity was assessed in this work. The phosphonium COFs show good thermal stability with Td,5% up to 435 °C. Increasing the phosphonium content (50%) leads to concomitantly better alkaline stability upon challenging the material in 6 M NaOH(aq) at 65 °C for 120 h. The specific surface areas estimated by BET for the materials are in the range of 3-63 m2/g. Decreasing phosphonium content leads to larger specific areas due to a more open-structure solid. P3, in which 33% of monomers comprise a phosphonium moiety, exhibited the highest CO2 affinity.
Yang, Xiaoyan, "Synthesis and Structure-Property Relationship of Phosphonium Polymers" (2017). All Dissertations. 2541.