Synthesis and characterization of new phosphorus and other heteroatom containing aryl cyanate ester monomers and networks

Several aromatic dicyanate monomers have been synthesized bearing para-linked strong electron withdrawing groups, such as phenylphosphine oxide, sulfone, and carbonyl. These groups increased the reactivity of the cyanate functional groups and eliminated the need for curing catalysts. However, an undesirable decrease in the processing window between the monomer melting point and the onset of cure was also generally observed. An arylene ether phenyl phosphine oxide system was designed that displayed several attractive characteristics such as a low softening point, a wide processing window, cure with no catalyst, high T_g and high char yield in air, suggesting that these new thermosets might show good fire resistance. The dicyanate ester monomers were synthesized in high yield by reacting various bisphenols with cyanogen bromide in the presence of triethylamine. The high reactivity of the cyanate functional groups required that the cyanation reaction be conducted at temperature below 0°C in order to prevent imidocarbonate side reactions. Proton NMR and FT-IR were used to characterize these monomers. The cyclotrimerization curing process was monitored by the disappearance of the carbon-nitrogen triple bond stretch (2270 cm⁻¹). An optimal cure schedule was determined and the cured polycyanurate networks were characterized by DSC, DMTA, and TGA. Tg values were typically > 250°C and 5% weight loss values were observed by TGA in air above 400°C. Several of the dicyanate monomers with sufficiently large processing windows were cured into single lap shear adhesive bonds onto titanium 6/4 and the measurements are reported herein. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 977–987, 1997     

Xenon Trioxide Adducts of O-Donor Ligands; [(CH3)2CO]3XeO3, [(CH3)2SO]3(XeO3)2, (C5H5NO)3(XeO3)2, and [(C6H5)3PO]2XeO3

Xenon trioxide (XeO₃) forms adducts with triphenylphosphine oxide, dimethylsulfoxide, pyridine-N-oxide, and acetone by coordination of the ligand oxygen atoms to the Xe^VI atom of XeO₃. The crystalline adducts were characterized by low-temperature, single-crystal X-ray diffraction, and Raman spectroscopy. Unlike solid XeO₃, which detonates when mechanically or thermally shocked, solid (C₅H₅NO)₃(XeO₃)₂, [(C₆H₅)₃PO]₂XeO₃, and [(CH₃)₂SO]₃(XeO₃)₂ are insensitive to mechanical shock. The [(CH₃)₂SO]₃(XeO₃)₂ adduct slowly decomposes over several days to (CH₃)₂SO₂, Xe, and O₂. All three complexes undergo rapid deflagration when ignited by a flame. Both [(C₆H₅)₃PO]₂XeO₃ and (C₅H₅NO)₃(XeO₃)₂ are room-temperature stable and the [(CH₃)₂CO]₃XeO₃ complex dissociates at room temperature to form a stable solution of XeO₃ in acetone. The xenon coordination sphere of [(C₆H₅)₃PO]₂XeO₃, a distorted square-pyramid, provides the first example of a five-coordinate XeO₃ complex with only two Xe- - -O adduct bonds. The xenon coordination spheres of the remaining adducts are distorted octahedra, comprised of three Xe- - -O secondary bonds that are approximately trans to the primary Xe−O bonds of XeO₃. Quantum-chemical calculations were used to assess the nature of the Xe- - -O adduct bonds, which are described as predominantly electrostatic bonds between the nucleophilic oxygen atoms of the bases and the σ-holes of the electrophilic xenon atoms.     

Crystallization of bisphenol-A polycarbonate induced by organic salts: Chemical modification of the polymer. II. Model reactions

In the presence of sodium o-chlorobenzoate, bisphenol-A diphenylcarbonate (BADPC) undergoes complex chemical modifications from 170°C. Reaction between BADPC and minute amounts of salt produces sodium phenoxide end groups which undergo a fast exchange reaction with the carbonate groups of BADPC. In a closed system, an equilibrium molecular weight distribution is progressively attained which agrees fairly well with the one predicted from a simple model based on Bernoulli statistics. In an open system, the equilibrium is continuously displaced by the evaporation of volatile diphenyl carbonate. This leads to a steady increase of the molecular weight.     

Study of the dynamics of the roots of a low-voltage break-arc

In this paper, a preceding study is resumed (see Velleaud et al., ibid., vol.19, no.3, p.510-4 (1991)). A few modifications have been brought to the mathematical model used to process the induction signals measured. Thus, the dynamics of the anodic and cathodic roots of a 2500 A break-arc at 200 V can be obtained with a set up almost similar to a low-voltage circuit breaker     

XPS study of Eu(III) coordination compounds: Core levels binding energies in solid mixed-oxo-compounds EumXxOy

Literature is relatively sparse on XPS studies of europium compounds: it is essentially restricted to metallic compounds (EuM₅, in which M is a transition metal) or to simple oxides. While particular interest have been devoted to understanding physical phenomenon in the beginning of “shake-down” and “shake-up” satellites evidenced on core-level regions of the lanthanides, few information on absolute binding energies (BE) was available. This paper reports an XPS binding energy data base for europium(III) compounds, in which Eu cation have various chemical environments: simple oxide Eu₂O₃, Eu mixed oxides with organic oxalate, acetylacetonate or inorganic sulfate, nitrate, carbonate ligands. The values of core-level BE (O_1s, Eu_3d and Eu_4d) and the characteristics of shake-down satellites of Eu_3d are reported, and their variations are attributed to ionicity/covalency changes. Such interpretation was already published for Group A mixed oxides and zeolites. These data are needed for determining Eu(III) species sorbed onto minerals in the presence of various ligands in the framework of retention studies for assessing the safety of future nuclear waste disposals.     

Stabilisation des vinyl- et ethynyl-phosphines secondaires par complexation du phosphore

A stable divinylphosphine P-W(CO)₅ complex is prepared in 2 steps from the corresponding divinyl-diethylaminophosphine complex by cleavage of the P-N bond by HCl followed by reduction of the P-Cl bond thus formed by LiAlH₄; a similar scheme is used for the synthesis of stable tungsten complexes of vinyl- and phenylethynyl-diethylaminophosphines.     

Control of a network of Euler-Bernoulli beams

The aim is to study the boundary controllability of a system modeling the vibrations of a network of N Euler-Bernoulli beams connected by n vibrating point masses. Using the classical Hilbert Uniqueness Method, the control problem is reduced to the obtention of an observability inequality. The solution is then expressed in terms of Fourier series so that it is also enough to show that the distance between two consecutive large eigenvalues of the spatial operator involved in this evolution problem is superior to a minimal fixed value. This property called spectral gap holds as soon as the roots of a function denoted by f_∞ (and giving the asymptotic behaviour of the eigenvalues) are all simple. For a network of N=2 different beams, this assumption on the multiplicity of the roots of f_∞ (denoted by (A)) is proved to be satisfied and controllability follows. For higher values of N, a numerical approach allows one to prove (A) in many situations and no counterexample has been found but the problem of giving a general proof of controllability remains open.     

The problem of the imperfection of a world,itself created by a perfect god

The two main arguments concern(1) the presence of an enlightened complementarity between philosophic (including scientific) and religious (not including mystic) thought, and(2) the necessity to postulate a threefold relationship whenever one is to gain knowledge of any kind. They are both inspired by physics (from Bohr's strict complementarity, resp. from Newton's fundamental postulate).God's perfection resides at least in Symmetry in a generalized (not restrictively spatial) sense. Yet, as the argument goes, Space does not exist as a thing. Consequently, the Great Geometer (God) cannot dwell within a World He creates, and it is wrong to speak about His (God's) existence; for, existence is bound to the temporal, and Time is, together with the World, part of God's creation. Thus the only possible creation consists in God separating World and Time from Himself: This is the paradigm of Symmetry-breaking.Polytheistic mythologies all assume such and such imperfection of their deities; hence perfection is meaningful for monotheism only. A relationship of a threefold (trinitary) nature must then obtain between God, World, and Time; this is analogous to Newton's postulate relating force, momentum and time. Just as the latter and its specific generalizations must be found true by verification, the said threefold relationship must also be found true: within philosophic thoughtmore geometrico (in a generalized sense), within religious thoughtmore hymnometrico. Yet the complementarity (called enlightened) arising between the two kinds of thought is of a higher nature than Bohr's strict complementarity. While it can be understood from the role assumed by language itself, it can however only be disposed of within mystic contemplation.Dedicated to Sir KARL POPPER on the occasion of his 90th birthday.     

Investigations on the interactions between Li-TFSI and glass fibers in the ternary PP/GF/Li-TFSI composites

The polypropylene/glass fiber(PP/GF) composites with excellent antistatic performance and improved mechanical properties have been reported by incorporation of a very small amount of the organic salt, lithium bis(trifluoromethanesulfonyl)imide(Li-TFSI), into the PP/GF composites. It was considered that GF could play the role as the pathways for the movements of ions in the ternary composites. In this work, the interactions between Li-TFSI and glass fiber and the effects of such interactions on the physical properties of the composites have been systematically investigated. Three types of glass fibers with different ―OH group concentrations have been prepared in order to compare the interactions between GF and Li-TFSI. It was found that the ―OH group concentrations on the surface of glass fiber have significant effects on interactions between glass fibers and Li-TFSI. Such interactions are crucial for both the antistatic and mechanical performances of the final PP/GF/Li-TFSI composites. The investigation indicated that the GF with high ―OH group concentrations confined the movement of TFSI-, which decreased the antistatic properties of PP/GF/Li-TFSI composites. On the other hand, the GF with low ―OH group concentrations inhibited the absorption of Li-TFSI onto the GF, which also hindered the formation of Li-TFSI conductive pathway. The best antistatic performance of the ternary composites can be achieved at the intermediate ―OH concentrations on the GF.