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Many structure/property relationships of hydrolyzed poly(ester urethane) (PEU) – a thermoplastic – have been reported. Examples include changes in molecular weight vs. elongation at break and crosslink density vs. mechanical strength. However, the effect of molecular weight (or molar mass) reduction on some physical, thermal, and chemical properties of hydrolyzed PEU have not been reported. Therefore, a large set of hydrolyzed PEU (Estane®5703) samples were obtained from two aging experiments: 1) accelerated aging conducted under various environments (air, nitrogen, moisture) and at 64 °C and below for almost three years, and 2) natural aging conducted under ambient conditions for moremore » than three decades. The hydrolyzed samples were characterized via multi-detection gel permeation chromatography (GPC), thermogravimetric analysis (TGA), modulated differential scanning calorimetry (mDSC), UV–vis spectroscopy, nuclear magnetic resonance (NMR), and Fourier-transform infrared (FTIR) spectroscopy techniques. Hydrolysis of ester linkages in the soft-segments decreases both the molecular weight (M_w) and the melting point (T_m) of Estane (from ~55 °C to 39 °C). Aging above this T_m, increased mobility of polymer chains and water diffusivity in the PEU matrix alter the PEU degradation pathway from those expected at aging temperatures below this T_m and have significant bearing on the critical molecular weight (M_C) at which the physical, chemical, thermal, and mechanical properties of Estane change abruptly. While a M_C value of 20 kDa is found for PEU hydrolysis at mild temperatures (e.g., as low as 39 °C), the value of M_C increases with increasing aging temperatures. To complement the existing structure/property relationships reported in the literature, more correlations are obtained, which include the effect of M_w on polydispersity, intrinsic viscosity (Mark-Houwink equation), UV extinction coefficient, and dn/dc (GPC analysis) values. Furthermore, we seek to bolster previously reported aging models for PEU by developing a practical model with which the extent of degradation and material performance can be predicted based on aging under different temperature ranges both above and below the melting point of Estane.« less

Abstract Reduction of Cp*( ^Tripp TerN)UI with KC ₈ generates (KCp*( ^Tripp TerN)UI) ₂ , the first example of a trivalent uranium imido, a previously elusive species, which are commonly unstable. Experimental and computational results indicate that the K ⁺ coordination is responsible for this isolable U(III) monoimido complex.

Organophosphorus nerve agents (OPAs) are a toxic class of synthetic compounds that cause adverse effects with many biological systems. Development of methods for environmental remediation and passivation has been ongoing for years. However, little progress has been made in therapeutic development for exposure victims. Given the postexposure behavior of OPA materials in enzymes such as acetylcholinesterase (AChE), development of electrophilic compounds as therapeutics may be more beneficial than the currently employed nucleophilic countermeasures. In this report, we present our studies with an electrophilic, 16-electron manganese complex (^iPrPNP)Mn(CO)₂ (1) and the nucleophilic hydroxide derivative (^iPrPN^HP)Mn(CO)₂(OH) (2). The reactivity of 1 withmore » phosphorus acids and the reactivity of 2 with the P–F bond of diisopropylfluorophosphate (DIPF) were studied. The role of water in both nucleophilic and electrophilic reactivity was investigated with the use of ¹⁷O-labeled water. Promising results arising from reactions of both 1 and 2 with organophosphorus substrates are reported.« less

Here, the first uranium bis(acyl)phosphide (BAP) complexes were synthesized from the reaction between sodium bis(mesitoyl)phosphide (Na(^mesBAP)) or sodium bis(2,4,6-triisopropylbenzoyl)phosphide (Na(^trippBAP)) and UI₃(1,4-dioxane)_1.5. Thermally stable, homoleptic BAP complexes were characterized by single-crystal X-ray diffraction and electron paramagnetic resonance (EPR) spectroscopy, when appropriate, for the elucidation of the electronic structure and bonding of these complexes. EPR spectroscopy revealed that the BAP ligands on the uranium center retain a significant amount of electron density. The EPR spectrum of the trivalent U(^trippBAP)₃ has a rhombic signal near g = 2 (g₁ = 2.03; g₂ = 2.01; and g₃ = 1.98) that is consistent withmore » the EPR-observed unpaired electron being located in a molecular orbital that appears ligand-derived. However, upon warming the complex to room temperature, no resonance was observed, indicating the presence of uranium character.« less

A method to explore head-to-head Φ back-bonding from uranium f-orbitals into allyl π* orbitals has been pursued. Anionic allyl groups were coordinated to uranium with tethered anilide ligands, then the products were investigated by using NMR spectroscopy, single-crystal XRD, and theoretical methods. The (allyl)silylanilide ligand, N-((dimethyl)prop-2-enylsilyl)-2,6-diisopropylaniline (LH), was used as either the fully protonated, singly deprotonated, or doubly deprotonated form, thereby highlighting the stability and versatility of the silylanilide motif. A free, neutral allyl group was observed in UI₂(L1)₂(1), which was synthesized by using the mono-deprotonated ligand [K][N-((dimethyl)prop-2-enyl)silyl)-2,6-diisopropylanilide] (L1). The desired homoleptic sandwich complex U[L2]2 (2) was prepared from allmore » three ligand precursors, but the most consistent results came from using the dipotassium salt of the doubly deprotonated ligand [K]₂[N-((dimethyl)propenidesilyl)-2,6-diisopropylanilide] (L2). This allyl-based sandwich complex was studied by using theoretical techniques with supporting experimental spectroscopy to investigate the potential for phi (Φ) back-bonding. The bonding between U^IV and the allyl fragments is best described as ligand-to-metal electron donation from a two carbon fragment-localized electron density into empty f-orbitals.« less

The addition of 2 equiv of ^tBu₂PSiMe₃ to 2,6-pyridinedicarboxaldehyde ((CHO)₂Py) results in a rac/meso diastereomeric mixture of the PNP-chelating ligand 2,6-bis((trimethylsiloxy)(di-tert-butylphosphino)-methyl)-pyridine (^(OTMS)PNP^tBu) (1-r/m) via addition of the P–Si bond across both of the aldehyde C–O bonds. Chelation of ^(OTMS)PNP^tBu to FeCl₂ results in the same diastereotopic ratio of (^(OTMS)PNP^tBu)FeCl₂ (2-r/m) as the free ligand. Fractional crystallization allows for the isolation of the C₂ isomer, 2-r, and a template synthesis protocol allows for the synthesis and isolation of the C_s isomer, 2-m, in good yield. Furthermore, the template synthesis protocol was also expanded to the f-block with the use of UCl₄more » in order to assess the specificity of the template synthesis on a larger metal cation. This reaction performed on UCl₄ forms the meso diastereospecific uranium complex (^(tBu2P)ONO)UCl₂(dtbpy), 3-m, with observation of the rational intermediate (^(OTMS)PNO^tBu)UCl₃(dtbpy), 4-m, which arose from the respective formation of two- or one-equivalents of TMS–Cl and formation of the corresponding U–O bond.« less