DESIGNING DYNAMIC AND DEGRADABLE POLYMERIC MATERIALS WITH THIOL-X CHEMISTRIES

With plastic production poised to increase in coming years, there arises a need to develop new polymeric materials designed to combat the global pollution crisis. A commonly utilized approach in addressing this challenge is to employ a responsive functional moiety into the polymer architecture. Thiol-X reactions, a commonly utilized class of “click” reactions, have garnered broad implementation in new stimuli-responsive materials. This work specifically focuses on utilizing radical-mediated thiol-ene coupling and base-catalyzed thiol-isocyanate reactions to develop a library of ternary thiol-ene/thiourethane covalent adaptable networks (CANs) and hydrolytically labile poly(thioether ketal) thermoplastics. CANs are a class of network materials capable of undergoing dynamic exchange, rendering the material reprocessable while maintaining the high-performance properties traditionally associated with thermosets. Herein, the thiourethane moiety, formed via the thiol-isocyanate reaction, is employed as the dynamic covalent chemistry (DCC) utilized in our approach to CANs. Additionally, linear thiol-ene photopolymerizations are employed to develop a series of poly(thioether ketal) thermoplastics. The ketal moiety incorporated into the polymer backbone of these materials render the resulting material hydrolytically labile – allowing the material to readily degrade at its end-of-lifetime. The work presented herein should provide a framework by which new environmentally friendly materials can be developed. Chapter I of this dissertation focuses on the various utility of thiol-X reactions within the realm of polymeric materials – with specific interest on implementation within CANs and thermoplastic synthesis. Chapter II outlines the methods by which the thiol-X based materials, described herein, were developed and studied. Chapter III focuses on understanding the specific structure-property relationship of ternary thiol-ene/thiourethane CANs affecting vitrimeric relaxation behaviors and material property retention throughout reprocessing. Chapter IV elaborates on the stoichiometric effects of ternary thiol-ene/thiourethane on the dynamic exchange equilibrium – ultimately dictating thermal relaxation behaviors. Finally, Chapter V utilizes linear thiol-ene photopolymerizations to develop a library of poly(thioether ketals) capable of undergo hydrolysis within an acidic environment while remaining stable in basic and neutral conditions

Characterization of Epoxy/Amine Networks with Glycidal Polyhedral Oligomeric Silsesquioxane Surface Modified Silica Nanoparticles

Silica nanoparticles were surface modified with octa-functional glycidal polyhedral oligomeric silsesquioxane (G-POSS) and incorporated into an epoxy/amine system in an effort to increase the mechanical performance of the inorganic/organic hybrid material. The silica nanoparticles were first functionalized with 3-aminoprpyltrimethoxysilane (APTMOS) at 5 and 10 weight percent, and then modified with G-POSS at ratios of 1:10 and 1:5 (APTMOS: G-POSS). The modified particles were then incorporated into an epoxy/amine network consisting of diglycidyl ether of bisphenol A (DGEBA) and aromatic amine, diamine diphenyl sulfone (4,4’ DDS) at 1 and 5 weight percent, resulting in 8 different formulations. The incorporation of the modified silica nanoparticles caused changes in crosslink density depending on the amount functionalization density, G-POSS modification, and loading. Samples with nanoparticles of higher functionalization density and lower G-POSS modification exhibited higher crosslink density due to high functionalization and lower free volume. It was determined that incorporation of inorganic POSS cage disrupted network formation and chain packing. Similar trends follow suite with the strength of the material in compressive analysis. The incorporation of the nanoparticles slightly decreased the gel point of the material as compared to that of the control. Furthermore, it was determined that there is an optimum degree of modification and loading that would influence the mechanical properties and performance of the material to its optimal values

Fairy Tale Retellings for the Modern World.

Fairy Tale Retellings for the Modern World. Panel by Sarena Ulibarri, Reese Hogan, Charlotte Honigman, Wendy Nikel, and Lissa Sloan. Tech Mod: Joan Marie Verba

Rational Design of Superhydrophilic/Superoleophobic Surfaces for Oil-Water Separation via Thiol-Acrylate Photopolymerization

We report a simple, rapid, and scalable strategy to fabricate surfaces exhibiting in-air superoleophobic/superhydrophilic wetting via sequential spray deposition and photopolymerization of nanoparticle-laden thiol–acrylate resins comprising both hydrophilic and oleophobic chemical constituents. The combination of spray deposition with nanoparticles provides hierarchical surface morphologies with both micro- and nanoscale roughness. Mapping the wetting behavior as a function of resin composition using high- and low-surface-tension liquid probes enabled facile identification of coatings that exhibit a range of wetting behavior, including superhydrophilic/superoleophilic, superhydrophobic/superoleophobic, and in-air superhydrophilic/superoleophobic wetting. In-air superhydrophilic/superoleophobic wetting was realized by a dynamic rearrangement of the interface to expose a greater fraction of hydrophilic moieties in response to contact with water. We show that these in-air superoleophobic/superhydrophilic coatings deposited onto porous supports enable separation of model oil–water emulsions with separation efficiencies up to 99.9% with 699 L·m–2 h–1 permeate flux when the superhydrophilic/superoleophobic coatings are paired with 0.45 μm nylon membrane supports

A multi-institutional study evaluating and describing atypical parathyroid tumors discovered after parathyroidectomy

Objective: To describe common intraoperative and pathologic findings of atypical parathyroid tumors (APTs) and evaluate clinical outcomes in patients undergoing parathyroidectomy. Methods: In this multi-institutional retrospective case series, data were collected from patients who underwent parathyroidectomy from 2000 to 2018 from three tertiary care institutions. APTs were defined according to the AJCC eighth edition guidelines and retrospective chart review was performed to evaluate the incidence of recurrent laryngeal nerve injury, recurrence of disease, and disease-specific mortality. Results: Twenty-eight patients were identified with a histopathologic diagnosis of atypical tumor. Mean age was 56 years (range, 23-83) and 68% (19/28) were female. All patients had an initial diagnosis of primary hyperparathyroidism with 21% (6/28) exhibiting clinical loss of bone density and 32% (9/28) presenting with nephrolithiasis or renal dysfunction. Intraoperatively, 29% (8/28) required thyroid lobectomy, 29% (8/28) had gross adherence to adjacent structures and 46% (13/28) had RLN adherence. The most common pathologic finding was fibrosis 46% (13/28). Postoperative complications include RLN paresis/paralysis in 14% (4/28) and hungry bone syndrome in 7% (2/28). No patients with a diagnosis of atypical tumor developed recurrent disease, however there was one patient that had persistent disease and hypercalcemia that is being observed. There were 96% (27/28) patients alive at last follow-up, with one death unrelated to disease. Conclusion: Despite the new AJCC categorization of atypical tumors staged as Tis, we observed no recurrence of disease after resection and no disease-specific mortality. However, patients with atypical tumors may be at increased risk for recurrent laryngeal nerve injury and incomplete resection

Current assessment of the Red Rectangle band problem

In this paper we discuss our insights into several key problems in the identification of the Red Rectangle Bands (RRBs). We have combined three independent sets of observations in order to try to define the constraints guiding the bands. We provide a summary of the general behavior of the bands and review the evidence for a molecular origin of the bands. The extent, composition, and possible absorption effects of the bands are discussed. Comparison spectra of the strongest band obtained at three different spectral resolutions suggests that an intrinsic line width of individual rotational lines can be deduced. Spectroscopic models of several relatively simple molecules were examined in order to investigate where the current data are weak. Suggestions are made for future studies to enhance our understanding of these enigmatic bands

Improved annotation of the insect vector of citrus greening disease: Biocuration by a diverse genomics community

The Asian citrus psyllid (Diaphorina citri Kuwayama) is the insect vector of the bacterium Candidatus Liberibacter asiaticus (CLas), the pathogen associated with citrus Huanglongbing (HLB, citrus greening). HLB threatens citrus production worldwide. Suppression or reduction of the insect vector using chemical insecticides has been the primary method to inhibit the spread of citrus greening disease. Accurate structural and functional annotation of the Asian citrus psyllid genome, as well as a clear understanding of the interactions between the insect and CLas, are required for development of new molecular-based HLB control methods. A draft assembly of the D. citri genome has been generated and annotated with automated pipelines. However, knowledge transfer from well-curated reference genomes such as that of Drosophila melanogaster to newly sequenced ones is challenging due to the complexity and diversity of insect genomes. To identify and improve gene models as potential targets for pest control, we manually curated several gene families with a focus on genes that have key functional roles in D. citri biology and CLas interactions. This community effort produced 530 manually curated gene models across developmental, physiological, RNAi regulatory and immunity-related pathways. As previously shown in the pea aphid, RNAi machinery genes putatively involved in the microRNA pathway have been specifically duplicated. A comprehensive transcriptome enabled us to identify a number of gene families that are either missing or misassembled in the draft genome. In order to develop biocuration as a training experience, we included undergraduate and graduate students from multiple institutions, as well as experienced annotators from the insect genomics research community. The resulting gene set (OGS v1.0) combines both automatically predicted and manually curated gene models.Peer reviewedBiochemistry and Molecular BiologyEntomology and Plant Patholog

Epoxy Hybrid Networks With High Mass Fraction Molecular-Level Dispersion of Pendant Polyhedral Oligomeric Silsesquioxane (POSS)

A novel high shear continuous reactor method was developed to obtain molecular level incorporation of polyhedral oligomeric silsesquioxane (POSS) containing one amine group and seven isobutyl groups into epoxy network as pendant cage. The method consisted of optimizing reaction time and temperature for the synthesis of POSS-epoxy precursor in a high shear continuous reactor. A full conversion of POSS into POSS-epoxy precursor was achieved within 30–40 s of reaction time in a continuous reactor for all molar compositions from 1:140 to 1:1.05 in comparison to a batch process with the reaction time of 18 h. The structure of this precursor at the end of the reaction, determined by silicon Nuclear Magnetic Resonance spectroscopy (29Si NMR), was close to the ideal one. The distribution of reaction product was determined by size exclusion chromatography (SEC). The reaction product containing up to 1:3-mol ratio of POSS: epoxy molecules showed ‘epoxy-POSS-epoxy’ precursor as a primary product in comparison to 1:2 and 1:1.05-mol ratios with higher molecular weight precursor as the primary product. Hybrid networks containing up to 50 wt % POSS were prepared by curing these precursors with an aromatic amine curative 4, 4\u27diamino diphenyl methane (DDM). The resulting networks are completely transparent and no phase separation was observed by SEM and TEM in the course of polymerization despite the incompatibility of the isobutyl groups attached to the POSS with the aromatic epoxy-amine networks. In addition to that, DMA and TGA results prove that the introduction of high shear continuous reactor promotes the dispersion of pendant POSS to a molecular level into epoxy networks

Interactive Effects Of Hatching Variability And Experimental Warming On Larval Wood Frogs (Rana Sylvatica)

One of the consequences of recent anthropogenic-induced climate change is increased climate variability and changes in the frequency and intensity of extreme weather events. This increased variability in temperature and precipitation has also influenced the phenology of ontogenetic life history events of birds, insects, plants, and amphibians. These phenological shifts- specifically advancements- appear to be a common response to climate change globally. In amphibians, these shifts manifest in the form of earlier breeding date and smaller size at metamorphosis. Early breeding can increase tadpole exposure to extreme temperature fluctuations, which can result in higher rates of mortality as well as stalls in development that lengthen the larval period, increasing the risk that ponds dry before individuals can metamorphose. Increased water temperatures can induce rapid development in tadpoles of some species, thereby potentially mitigating this effect, however this comes with a tradeoff of individuals metamorphosing at smaller sizes