R-Silsesquioxane-Based Network Polymers by Fluoride Catalyzed Synthesis: An Investigation of Cross-Linker Structure and Its Influence on Porosity

Silsesquioxane-based networks are an important class of materials that have many applications where high thermal/oxidative stability and porosity are needed simultaneously. However, there is a great desire to be able to design these materials for specialized applications in environmental remediation and medicine. To do so requires a simple synthesis method to make materials with expanded functionalities. In this article, we explore the synthesis of R-silsesquioxane-based porous networks by fluoride catalysis containing methyl, phenyl and vinyl corners (R-Si(OEt)) combined with four different bis-triethoxysilyl cross-linkers (ethyl, ethylene, acetylene and hexyl). Synthesized materials were then analyzed for their porosity, surface area, thermal stability and general structure. We found that when a specified cage corner (i.e., methyl) is compared across all cross-linkers in two different solvent systems (dichloromethane and acetonitrile), pore size distributions are consistent with cross-linker length, pore sizes tended to be larger and π-bond-containing cross-linkers reduced overall microporosity. Changing to larger cage corners for each of the cross-linkers tended to show decreases in overall surface area, except when both corners and cross-linkers contained π-bonds. These studies will enable further understanding of post-synthesis modifiable silsesquioxane networks

Thermally Stable Fluorogenic Zn(II) Sensor Based on a Bis(benzimidazole)pyridine-Linked Phenyl-Silsesquioxane Polymer

A 2,6-bis(2-benzimidazolyl) pyridine-linked silsesquioxane-based semi-branched polymer was synthesized, and its photophysical and metal-sensing properties have been investigated. The polymer is thermally stable up to 285 °C and emits blue in both solid and solution state. The emission of the polymer is sensitive to pH and is gradually decreased and quenched upon protonation of the linkers. The initial emission color is recoverable upon deprotonation with triethylamine. The polymer also shows unique spectroscopic properties in both absorption and emission upon long-term UV irradiation, with red-shifted absorption and emission not present in a simple blended system of phenylsilsesquioxane and linker, suggesting that a long-lived energy transfer or charge separated state is present. In addition, the polymer acts as a fluorescence shift sensor for Zn(II) ions, with red shifts observed from 464 to 528 nm, and reversible binding by the introduction of a competitive ligand such as tetrahydrofuran. The ion sensing mechanism can differentiate Zn(II) from Cd(II) by fluorescence color shifts, which is unique because they are in the same group of the periodic table and possess similar chemical properties. Finally, the polymer system embedded in a paper strip acts as a fluorescent chemosensor for Zn(II) ions in solution, showing its potential as a solid phase ion extractor

Synthesis and investigation of silsesquioxane networks from static to photoactive smart materials

Materials Chemistry is an extremely important area of science touching everything from solar energy conversion to medical implants. The work of this dissertation has focused on developing porous materials, especially related to functional and stimuli responsive materials, including photochemical, for a variety of applications such as environmental remediation, soft robotics, and self-healing materials. We aimed to create silicon-based materials to overcome many of the technological barriers including low thermal stability, low selectivity, and poor mechanical properties of the typical materials used in these types of applications. Chapter 1 gives an overview and background of the types of materials that will be investigated in this dissertation. We will first introduce silsesquioxane (RSiO1.5)n chemistry, including synthesis methodologies, synthetic challenges and the properties that give reasons for their use. The research detailed in chapters 2 and 3 of this dissertation set out to contribute a new synthetic method for silicon-based porous materials involving fluoride catalyzed polymerization of R-alkoxysilanes. We aimed to gain a fundamental understanding of the reaction parameters and their impact on structure-property relationships in porous silsesquioxane-based gel materials. In chapter 4, we explored the interaction of fluoride with a silica-based cage called octa(dimethylsiloxy)silsesquioxane (Q8M8H). While it was expected that little interaction would occur with Q8M8H it was found that the outer siloxane units undergo rapid self-polymerization in the presence of a fluoride anion catalyst to form complex 3D porous structural network materials with specific surface areas up to 650 m2g-1. In chapter 5, we demonstrate our approach to photoswitchable silicon-based network polymers using Q8M8H as a cubic building block and azobenzene as a photo-actuatable cross-linker. We found that these photoswitchable silsesquioxane/azobenzene hybrid 3D–polymer gels can be effectively synthesized and show reversible photo-dynamic sponge characteristics. Lastly, in chapter 6 we discuss the impact of this work on the field and potential ways it can be moved forward to either gain a more fundamental understanding of reaction processes or greatly improve responsive performance of porous silsesquioxane-based materials

Formation of Nanostructured Silicas through the Fluoride Catalysed Self-Polymerization of Q-type Silsesquioxane Cages

Octa(dimethylsiloxy)silsesquioxane (Q8M8H) undergoes rapid self-polymerization in the presence of a fluoride catalyst to form complex 3D porous structural network materials with specific surface areas up to 650 m2g-1. This establishes a new method to bio-derived high inorganic content soft silicas with potential applications in filtration, carbon capture, catalysis, or hydrogen source

Effects of Functionalization on Photo-Actuatable Octa(dimethylsiloxy)silsesquioxane-Azobenzene Network Gels and their Substance Loading and Unloading Efficiencies

The synthesis, analysis, and effect on solvent uptake of styrene, alcohol, amino, and perfluoro functionalized silsesquioxane-azobenzene hybrid gels are discussed. 4,4’-diallyloxyazobenzene and octa(dimethylsiloxy)silsesquioxane (Q8M8H) gels are generated using hydrosilylation chemistry. These gels were modified through two routes: in-situ and post-synthesis modification, depending on the compatibility of the modifiers. The dynamic gel systems react to visible and UV light to expand and contract, giving them sponge-like properties. The effects on their solvent uptake load and preference for various solvents/pollutants are detailed below, and general characteristics are illustrated through FTIR, TGA, and SEM imaging. We find that selectivity for certain substances can be obtained but at the cost of total absorptivity of the gel systems

An efficient multi-doping strategy to enhance Li-ion conductivity in the garnet-type solid electrolyte Li7La3Zr2O12

Lithium-ion (Li + ) batteries suffer from problems caused by the chemical instability of their organic electrolytes. Solid-state electrolytes that exhibit high ionic conductivities and are stable to lithium metal are potential replacements for flammable organic electrolytes. Garnet-type Li 7 La 3 Zr 2 O 12 is a promising solid-state electrolyte for next-generation solid-state Li batteries. In this study, we prepared mono-, dual-, and ternary-doped lithium (Li) garnets by doping tantalum (Ta), tantalum-barium (Ta-Ba), and tantalum-barium-gallium (Ta-Ba-Ga) ions, along with an undoped Li 7 La 3 Zr 2 O 12 (LLZO) cubic garnet electrolyte, using a conventional solid-state reaction method. The effect of multi-ion doping on the Li + dynamics in the garnet-type LLZO was studied by combining joint Rietveld refinement against X-ray diffraction and high-resolution neutron powder diffraction analyses with the results of Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and multinuclear magic angle spinning nuclear magnetic resonance. Our results revealed that Li + occupancy in the tetrahedrally coordinated site (24d) increased with increased multi-ion doping in LLZO, whereas Li + occupancy in the octahedrally coordinated site (96h) remained constant. Among the investigated compounds, the ternary-doped garnet structure Li 6.65 Ga 0.05 La 2.95 Ba 0.05 Zr 1.75 Ta 0.25 O 12 (LGLBZTO) exhibited the highest total ionic conductivity of 0.72 and 1.24 mS cm -1 at room temperature and 60 °C, respectively. Overall, our findings revealed that the dense microstructure and increased Li + occupancy in the tetrahedral-24d Li1 site played a key role in achieving the maximum room-temperature Li-ion conductivity in the ternary-doped LGLBZTO garnet, and that the prepared ternary-doped LGLBZTO was a potential solid electrolyte for Li-ion batteries without polymer adhesion

Risk analysis of use of different classes of antidepressants on subsequent dementia: A nationwide cohort study in Taiwan

<div><p>Depression and dementia are common mental health problems and are associated in several ways. Early-life depression is associated with increased risk of later life dementia, and depression can present as a preclinical symptom or consequence of dementia. Despite the plausible relationship between these two clinical entities, the potential association between antidepressant medication and dementia has rarely been investigated. We conducted a 9-year retrospective analysis of Taiwan’s National Health Insurance Research Database (NHIRD), enrolling 5819 cases who had received prescriptions of antidepressants between 2003 and 2006, and 23,276 (with ratio of 1:4) age, sex, and index date-matched controls. The hazard ratio (HR) of dementia among antidepressant users with depression was 2.42 (95% confidence interval (CI): 1.15–5.10), for those without depression was 4.05 (95% CI: 3.19–5.15), compared to antidepressant non-users respectively. Among the 6 classes of common antidepressants used in Taiwan, the adjusted HRs were 3.66 (95% CI: 2.62–5.09) for SSRIs, 4.73 (95% CI: 2.54–8.80) for SNRI, 3.26 (95% CI: 2.30–4.63) for TCAs, 6.62 (95% CI: 3.34–13.13) for TeCA, 4.94 (95% CI: 2.17–11.24) for MAOI, and 4.48 (95% CI: 3.13–6.40) for SARI. Furthermore, the multivariate analysis result showed that the adjusted HRs of cumulative defined daily doses (cDDDs) were 3.74 (95% CI: 2.91–4.82), 3.73 (95% CI: 2.39–5.80) and 5.22 (95% CI: 3.35–8.14) for those who had cDDDs of <90, 90–180 and >180 compared to those who had taken no antidepressant medication. This is a retrospective study based on secondary data, hence, we could not claim causality between antidepressant medication and dementia. However, a potential association between antidepressant and occurrence of dementia after controlling for the status of depression was observed. Lack of patients’ data about smoking status and body mass index in NHIRD, which are considered related to dementia, was also a limitation in this study. In this study, we concluded that antidepressant medication is a potential risk factor for dementia, independent from any effect of depression itself.</p></div

Assessment of risk factors for dementia using cox proportional hazards regression model.

<p>Assessment of risk factors for dementia using cox proportional hazards regression model.</p

Risk of dementia with the use of antidepressants from different classes (reference = control).

<p>Risk of dementia with the use of antidepressants from different classes (reference = control).</p

Comparison of demographic characteristics and risk factors between cases and controls.

<p>Comparison of demographic characteristics and risk factors between cases and controls.</p