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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Functional Polymers Containing Semi-Rigid Alternating Sequences

Huang, Jing 12 December 2017 (has links)
Alternating copolymers represent a special class of copolymers in which the two comonomers copolymerize in a regular alternating sequence along the polymer chain. Of particular interest in our group are the stilbene-maleic anhydride/maleimide alternating copolymers. These copolymers possess sterically congested backbones and precisely placed functional groups arising from the strictly alternating copolymerization. The research in this dissertation is focused on the synthesis, characterization, and potential application of functionalized copolymers that contain semi-rigid alternating copolymer sequences. The fluorescence properties of a series of non-conjugated, tert-butyl carboxylate functionalized alternating copolymers were investigated. Extraordinarily high fluorescent intensity with excellent linearity was observed for the di-tert-butyl group-containing stilbene and maleic anhydride alternating copolymer in THF. We attributed the origin of the strong fluorescence to the “through space” π – π interactions between the phenyl rings from the stilbene and C=O groups from the anhydride. The fluorescence was maintained when the copolymer was deprotected and hydrolyzed and the resulting carboxylic acid-functionalized copolymer was dissolved in water at neutral pH. The tert-butyl carboxylate functionalized alternating copolymer sequences were incorporated into highly crosslinked polymer networks using suspension polymerization. After removing the tert-butyl groups by acidic hydrolysis, the surface area of the networks increased significantly. Using this facile two-step strategy, we were able to achieve nanoporous polymers with BET surface area up to 817 m2/g and carboxylic acid-functionalized surfaces. The BET surface area of deprotected polymers increased with increasing crosslinking density, and the stilbene-containing polymers showed systematically higher BET surface area than the styrene-containing polymers due to the stiffness of the alternating sequences. The resulting nanoporous polymers have potential to be employed as solid sorbents for CO2. The same tert-butyl carboxylate functionalized alternating copolymer sequences were also incorporated into microgels via miniemulsion polymerization. The miniemulsion technique ensured the successful synthesis of microgels with ~100 nm diameter using solid stilbene and maleimide monomers. The resulting tert-butyl carboxylate-containing microgels were converted into carboxylic acid-containing aqueous microgels by acid hydrolysis. These aqueous microgels showed good and reversible lead and copper ion adsorption capacities. Amine-functionalized nanoporous polymers were synthesized by the post-modification of highly-crosslinked divinylbenzene-maleic anhydride polymers. High amine-contents were achieved by covalently attaching multiamines to the acid-chloride functionalized polymer surface. The resulting polymers showed medium to high BET surface areas (up to 500 m2/g) and high CO2 capture capacities. / PHD / Copolymers are polymers that consist of two or more different monomers in the polymer chain. Research on copolymers can be traced back to the 1930s. Since the early discoveries, the research on copolymers has received considerable attention because of the ease of synthesis and the versatile properties and applications of these materials. Alternating copolymers are one of the most studied types of copolymers. In an alternating copolymer, the two different monomers arrange in a regular alternating sequence along the polymer backbone. Of special interest in our group are the alternating copolymers that contain stilbene (1,2- diphenylethylene). The stilbene-containing alternating copolymers have relatively rigid (semi-rigid) structures, which lead to unusual and interesting properties. The research described in this dissertation is focused on incorporating these semi-rigid alternating copolymers into different types of systems and studying their structure/property relationships. Three different polymeric materials and their properties were explored. Fluorescent materials can glow when irradiated by a certain wavelength of light. This property is very useful in biomedical sensing, imaging and labeling. The semi-rigid stilbene-containing alternating copolymer exhibited fluorescence with extraordinarily high intensity, solely due to the conjugation from the exact juxtaposition of molecular orbitals. This high intensity fluorescence suggests potential application as novel light-emitting materials. The increasing atmospheric CO₂ concentrations due to human activities like transportation and manufacturing have caused public concerns. Currently, liquid amine scrubbing is one of the most well established methods for CO₂ capture in industry. However, due to the solvent evaporation, degradation, and the high energy demand during the solvent regeneration, solid polymeric materials are considered as attractive alternative CO₂ capture materials. We designed two kinds of polymers based on our semi-rigid alternating copolymer sequences, and they both exhibited pores smaller than 2 nm. With the help of different functional groups designed to interact with CO₂, these polymers showed enhancement in CO₂ capture properties, and show the viability as solid sorbents for atmospheric CO₂. Heavy metal contamination in water is a severe environmental and public health problem. The recent Flint water crisis raised the public awareness of this problem. We synthesized a series of hydrogel beads with diameters in the range of 100-200 nm. The incorporation of these functional alternating copolymer sequence into the microgels led to fast and reversible adsorption of the lead and copper ions in water.
2

Bacterial poly-gamma-glutamic acid (γ-PGA) : a promising biosorbent of heavy metals

Ogunleye, Adetoro O. January 2015 (has links)
Poly-γ-glutamic acid (γ-PGA) is a biopolymer made up of repeating units of L-glutamic acid, D-glutamic acid or both. γ-PGA is water soluble, non-toxic and biodegradable, and can be used safely in a variety of applications that are increasing rapidly. This study investigated the production of HMW γ-PGA by five Bacillus species (B. licheniformis 1525, B. licheniformis NCTC 6816, B. licheniformis ATCC 9945a, B. licheniformis ATCC 9945a and B. subtilis (natto) ATCC 15245) in GS, C and E media for the removal of heavy metals in wastewaters. The highest γ-PGA yields of 11.69 g/l and 11.59 g/l were produced by Bacillus subtilis (natto) ATCC 15245 in GS medium and medium C respectively. Upon characterization, γ- PGAs with different properties (crystallinity, acid/salt form and molecular weights ranging from 2.56 × 105 Da to 1.65 × 106 Da) were produced. The water soluble, non-toxic, HMW (Mw 1.65 × 106 Da) γ-PGA produced by B. subtilis (natto) ATCC 15245 in medium C was investigated as a sorbent for the removal of heavy metal ions including Cu2+, Zn2+, Ni2+, Cd2+ and Ag+. The results showed that the removal of metals by γ-PGA was more dependent on the concentration of γ-PGA than the solution pH. The highest metal ions removal of 93.50%, 88.13%, 90.21%, 90.56% and 86.34% by HMW γ-PGA were obtained for Cu2+, Zn2+, Ni2+, Cd2+ and Ag+ respectively. The presence of interfering metal ions could hinder the adsorption of individual metal ions by γ-PGA. The affinities of heavy metal ions for γ-PGA followed the order: Cu2+ > Zn2+ > Ni2+ > Cd2+. The effect of molecular weight of γ-PGA on metal removal was also investigated, and it was found that metal ion adsorption capacity of γ-PGA strongly depended on its molecular weight. The maximum amount (93.50%) of Cu2+ sorbed by HMW γ-PGA was higher compared to that (59.48%) sorbed by LMW γ-PGA. Isotherm models showed that the Redlich-Peterson best described the metal adsorption capacity of γ-PGA. It was also found that a multisite adsorption mechanism occurred via the complexation of metal ions with the free α-carboxyl and possibly the amide functional groups in γ-PGA.

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