All ETDs from UAB

Advisory Committee Chair

Gary M Gray

Advisory Committee Members

Houston Byrd

Tracy Hamilton

Eugenia Kharlampieva

Christopher Lawson

Document Type

Dissertation

Date of Award

2020

Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences

Abstract

Main-chain phosphorus polymers are still relatively unexplored, especially those of the polyphosphonite class in which phosphorus remains in a reactive P3+ oxidation state. This work established and builds upon a novel approach for generating these polymers from the reaction of a diol and bis(diethylamino)phosphine reagent and their subsequent conversion to variable polyphosphonates (P5+). Further, it explores their structure-function relationship through the use of NMR characterization, thermal analysis and molecular weight analysis. The applications of these polymers are also investigated based on their functional structure. The first chapter reports the first case in which polyphosphonites of reasonably high molecular weights and variable organic substituents were successfully synthesized from 1,12-dodecanediol and bis(diethylamino)(R)phosphine (R = phenyl or 2,2’-bithienyl) and subsequently converted to their respective polyphosphonates of variable Lewis acid substituents (P-O, P-S, or P-Se). Not only is this unique synthetic approach exhibited, but all reported polyphosphonates were highly characterized through NMR, SEC, thermal and (in certain cases) linear and nonlinear optical analysis. Polyphosphonates were thermally stable up to 290 ºC and SEC indicated ????̅ns as high as 4.3 × 104 Da. In cases were the organic substituent on the phosphorus was 2,2’-bithienyl, linear and nonlinear measurements were comparable to similar phosphonate-substituted 2,2’-bithienyl-5-yl molecular species. In the second chapter, the extent of modularity in these polyphosphonates was investigated by exploring additional backbone designs, variable Lewis acid adduct substituents and both homo- and copolymer designs. Backbones were varied through the reaction of additional diols (ranging from tetraethylene glycol to 1,4-benzenedimethanol) and bis(diethylamino)phenylphosphine. Random copolymers were made by using equal amounts of two diols, while block copolymers were made using a multi-step polymerization technique. All polymers possessed similar or improved thermal stabilities (up to ~310 ºC) to the polyphosphonates reported in chapter 1, and Tgs were shown to vary extensively depending on the rigidity of the backbone generated. Additionally, 31P{1H} NMR was shown to be exceptionally useful in analyzing the microstructure of these polymers due to the presence of phosphorus in the main chain. SEC data showed ????̅ws as high as 3.8 × 104 Da. Chapter 3 explores the use of tetraethylene glycol-based polyphosphonates as solid polymer electrolytes. Because of the similarity of these polymers to poly(ethylene oxide)s, they were doped with LiPF6 and shown to have similar or improved conductivities than similar organic polymers with the same salt system. More, there was an observed difference between polyphosphonates bearing P-S and P-Se Lewis acid substituents. Further studies were done using Li+ titrations monitored by 31P{1H} NMR that allowed the binding behavior between polymer and salt to be modeled. It was determined that Li+ exhibits positive cooperativity when interacting with the ethylene oxide segments of the polymers, and that the extent of cooperativity was higher in the polyphosphonate bearing selenium. It is hypothesized that the larger size of the selenium substituent leads to both increased conductivities at higher temperatures and increased cooperativity in solution. In the final chapter, homopolymer and copolymer polyphosphonates bearing anthracenyl organic substituents were studied as fluorescent materials. Employing the knowledge gained from the work of the previous chapters, the structural design of each polymer was changed to observe the effect this played on quantum yields and absorbance profiles. A homopolymer in which anthracenyl groups occurred in every repeat unit was compared to multiple copolymers in which the anthracenyl groups are randomly dispersed in a 1:10 or 1:20 ratio with phenyl groups. The copolymers showed significantly higher quantum yields (QF = 0.18 vs. 0.06) and the absorbance profile of the homopolymer exhibited an additional, higher energy maxima at ~335 nm. While most reported polyphosphonates in this work possessed sulfur substituents, one studied copolymer possessed selenium and surprisingly showed the lowest quantum yield of the studied polymers. This was believed to be due to a conversion of fluorescence to phosphorescence to intersystem crossing caused by the heavy selenium atoms. Overall, these polymers achieved fluorescence greater than that of anthracene-bearing poly(methyl methacrylate)s but lower than that of comparable molecular anthracenyl phosphonates.

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