Assessing the Effectiveness of Studio Physics at Georgia State University

Previous studies have shown that many students have misconceptions about basic concepts in physics which persist after instruction. It has been concluded that one of the challenges lies in the teaching methodology. To address this, Georgia State University (GSU) has begun teaching studio algebra-based physics. Although many institutions have implemented studio physics, most have done so in calculus-based sequences. Additionally, the unique environment of GSU’s population as a diverse, urban research institution is considered. The effectiveness of the studio approach for this demographic in an algebra-based introductory physics course was assessed. This five-semester pilot study presents demographic survey results and compares the results of student pre- and post-tests using the Force Concept Inventory (FCI). FCI results show that 1) the studio approach yields higher learning gains than the conventional course, 2) there are significant performance differences among ethnic groups, and 3) a gender gaps exists regardless of instructional method

Visible-Light-Induced Olefin Activation Using 3D Aromatic Boron-Rich Cluster Photooxidants

We report a discovery that perfunctionalized icosahedral dodecaborate clusters of the type B_(12)(OCH_2Ar)_(12) (Ar = Ph or C_6F_5) can undergo photo-excitation with visible light, leading to a new class of metal-free photooxidants. Excitation in these species occurs as a result of the charge transfer between low-lying orbitals located on the benzyl substituents and an unoccupied orbital delocalized throughout the boron cluster core. Here we show how these species, photo-excited with a benchtop blue LED source, can exhibit excited-state reduction potentials as high as 3 V and can participate in electron-transfer processes with a broad range of styrene monomers, initiating their polymerization. Initiation is observed in cases of both electron-rich and electron-deficient styrene monomers at cluster loadings as low as 0.005 mol%. Furthermore, photo-excitation of B_(12)(OCH_2C_6F_5)_(12) in the presence of a less activated olefin such as isobutylene results in the production of highly branched poly(isobutylene). This work introduces a new class of air-stable, metal-free photo-redox reagents capable of mediating chemical transformations

Nucleophilicity of Neutral versus Cationic Magnesium Silyl Compounds

Charge and ancillary ligands affect the reactivity of monomeric tris(trimethylsilyl)silyl magnesium compounds. Diamine-coordinated (tmeda)Mg{Si(SiMe3)3}Me (tmeda = tetramethylethylenediamine; 2-tmeda) and (dpe)Mg{Si(SiMe3)3}Me (dpe =1,2-N,N-dipyrrolidenylethane; 2-dpe) are synthesized by salt elimination reactions of L2MgMeBr and KSi(SiMe3)3. Compounds 2-tmeda or 2-dpe react with MeI or MeOTf to give MeSi(SiMe3)3 as the product of Si–C bond formation. In contrast, 2-tmeda and 2-dpe undergo exclusively reaction at the magnesium methyl group with electrophiles such as Me3SiI, B(C6F5)3, HB(C6F5)2, and [Ph3C][B(C6F5)4]. These reactions provide a series of neutral, zwitterionic, and cationic magnesium silyl compounds, and from this series we have found that silyl group transfer is less effective with cationic magnesium compounds than neutral complexes

Biomass-derived polymers and copolymers incorporating monolignols and their derivatives

Due to the importance of developing more sustainable commodity materials, this dissertation focuses on the synthesis and characterizarion of a series of polymers and copolymers from monolignols and other biomass components. The polymers described within were designed to feature a modular synthesis and were persued due to their structural similarities to commodity materials. Chapter 2 focuses on the synthetic development, thermal properties, and hydrolytic degradation of a series of monolignols-based poly(ester-amides) via interfacial polymerization with a monolignol-based ester dimer and aliphatic or aromatic diamines. These polymers were found to have differing thermal and degradation properties depending on the length (aliphatic) or structural (aromatic versus aliphatic) characteristics of the diamine utilized. Chapter 3 focuses on the development of the analogous monolignol-based poly(ether-amide) systems. These poly(ether-amide)s were synthesized used a monolignol-based ether dimer and aliphatic or aromatic diamines. As seen previously, the identity of the diamine linker played a role in the observed physical characteristics of the resulting polymers. Finally, Chapter 4 will focus on the development of a series of polymers from monolignols and citraconic anhydride as biologically-derived analogues to petroleum-based polystyrene-co-maleic anhydride and their use in polymer blends with commodity polymers. The monomers were polymerized using BF3Et2O as an initiator in cationic polymerization and the structure and physical properties of the resulting oligomers were then thoroughly studied. The oligomers were then used and studied in polymer blends with polystyrene and poly(lactic-acid). In summary, this dissertation focuses on the synthesis and study of several classes of polymeric materials generated directly from biomass components as chemical sources, with a focus on modularity and the tunability of observed properties

Biomass-derived polymers and copolymers incorporating monolignols and their derivatives

Due to the importance of developing more sustainable commodity materials, this dissertation focuses on the synthesis and characterizarion of a series of polymers and copolymers from monolignols and other biomass components. The polymers described within were designed to feature a modular synthesis and were persued due to their structural similarities to commodity materials. Chapter 2 focuses on the synthetic development, thermal properties, and hydrolytic degradation of a series of monolignols-based poly(ester-amides) via interfacial polymerization with a monolignol-based ester dimer and aliphatic or aromatic diamines. These polymers were found to have differing thermal and degradation properties depending on the length (aliphatic) or structural (aromatic versus aliphatic) characteristics of the diamine utilized. Chapter 3 focuses on the development of the analogous monolignol-based poly(ether-amide) systems. These poly(ether-amide)s were synthesized used a monolignol-based ether dimer and aliphatic or aromatic diamines. As seen previously, the identity of the diamine linker played a role in the observed physical characteristics of the resulting polymers. Finally, Chapter 4 will focus on the development of a series of polymers from monolignols and citraconic anhydride as biologically-derived analogues to petroleum-based polystyrene-co-maleic anhydride and their use in polymer blends with commodity polymers. The monomers were polymerized using BF3Et2O as an initiator in cationic polymerization and the structure and physical properties of the resulting oligomers were then thoroughly studied. The oligomers were then used and studied in polymer blends with polystyrene and poly(lactic-acid). In summary, this dissertation focuses on the synthesis and study of several classes of polymeric materials generated directly from biomass components as chemical sources, with a focus on modularity and the tunability of observed properties

Biodegradable Aromatic–Aliphatic Poly(ester–amides) from Monolignol-Based Ester Dimers

Biobased polymers with tunable properties have received increased attention in the literature due to a decline in petroleum reserves. Owing to its low cost, abundance, and aromatic structure, lignin has great potential as a feedstock for value-added polymeric products. In this work, we condensed carboxylic acid precursors with monolignols to generate reactive dimers for polymer synthesis. Three different aromatic ester dimers, each corresponding to a different monolignol, were synthesized and characterized. The dicarboxylic acid dimers were converted to the corresponding diacid chloride in situ with thionyl chloride, and a series of poly­(ester–amides) were synthesized via interfacial polymerization of these diacid chlorides with seven different aliphatic or aromatic diamines. The thermal properties (decomposition, glass transition temperature, and melting temperature) and hydrolytic stability in acidic and neutral aqueous conditions of the resulting polymers were studied

Synthesis and Characterization of Paramagnetic Lanthanide Benzyl Complexes

The organometallic chemistry of paramagnetic lanthanides (Ln, from Ce to Yb) is far less developed compared to that of their diamagnetic counterparts (Sc, Y, La, and Lu). Lack of available starting materials and characterization methods are the major obstacles. Herein we report the synthesis and characterization of trisbenzyl complexes of neodymium, gadolinium, holmium, and erbium. In addition, we introduce a direct procedure for the synthesis of lanthanide benzyl and iodide complexes supported by a ferrocene diamide ligand starting from the corresponding oxides. All newly synthesized compounds were characterized by X-ray crystallography, ¹H NMR spectroscopy (except for gadolinium compounds, which were NMR silent), and elemental analysis

Intermolecular β‑Hydrogen Abstraction in Ytterbium, Calcium, and Potassium Tris(dimethylsilyl)methyl Compounds

A series of organometallic compounds containing the tris­(dimethylsilyl)­methyl ligand are described. The potassium carbanions KC­(SiHMe₂)₃ and {KC­(SiHMe₂)₃TMEDA}₂ are synthesized by deprotonation of the hydrocarbon HC­(SiHMe₂)₃ with potassium benzyl. {KC­(SiHMe₂)₃TMEDA}₂ crystallizes as a dimer with two types of three-center–two-electron K–H–Si interactions: side-on coordination of SiH (∠K–H–Si = 102(2)°) and more obtuse K–H–Si structures (∠K–H–Si ≈ 150°). The divalent calcium and ytterbium compounds M­{C­(SiHMe₂)₃}₂L (M = Ca, Yb; L = 2THF, TMEDA) are prepared from MI₂ and 2 equiv of KC­(SiHMe₂)₃. Low ¹<i>J</i>_SiH coupling constants in the NMR spectra, low-energy ν_SiH bands in the IR spectra, and short M–Si distances and small M–C–Si angles in the crystal structures suggest β-agostic interactions on each C­(SiHMe₂)₃ ligand. The IR assignments of M­{C­(SiHMe₂)₃}₂L (L = 2THF, TMEDA) are supported by DFT calculations. The compounds M­{C­(SiHMe₂)₃}₂L react with 1 or 2 equiv of B­(C₆F₅)₃ to give the 1,3-disilacyclobutane {Me₂SiC­(SiHMe₂)₂}₂ and MC­(SiHMe₂)₃HB­(C₆F₅)₃L or M­{HB­(C₆F₅)₃}₂L, respectively. In addition, M­{C­(SiHMe₂)₃}₂L compounds react with BPh₃ to give β-H abstracted products. The compounds M­{C­(SiHMe₂)₃}₂THF₂ react with SiMe₃I to yield Me₃SiH and disilacyclobutane as the products of β-H abstraction, while M­{C­(SiHMe₂)₃}₂TMEDA and Me₃SiI form a mixture of Me₃SiH and the alkylation product Me₃SiC­(SiHMe₂)₃ in a 1:3 ratio