A number of thermosetting polyimide resin formulations have been prepared evaluated and used in the resin transfer molding (RTM) fabrication of S2-glass reinforced composite laminates. The resin formulations are based on combining varying amounts of 3, 4 ' -oxydianiline and 4, 4 ' -(1,3-phenylenedioxy) dianiline with 4, 4 ' -bisphenol A dianhydride and 3, 3 ' , 4, 4 ' -benzophenone tetracarboxylic dianhydride and terminated in 4-phenylethynyl phthalic anhydride. The initial viscosity and working life of the resins were measured to determine suitability for RTM. Composite laminates were prepared by degassing and then transferring the resins at 260 or 270 ° C. A laboratory RTM system with process capabilities to 300 ° C and 2000 psi, was built and utilized. The polyimide matrix was cured at 320 and 340 ° C, with a dwell for 3 h at each temperature, under 280 psi hydrostatic pressure. The effect of three different Co-60 gamma irradiation doses on cryogenic (77K) mechanical and thermal properties was determined. Performance was compared to that of laminates prepared from a commercially available bismaleimide (RTM-651 ® ). The composites are being studied for their potential use as the electrical insulation in the super-conducting magnet coils of future fusion reactor devices such as the International Thermonuclear Experimental Reactor.
A series of mixed-ligand 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) rhenium(I) dicarbonyl complexes that are emissive in fluid solution has been prepared, which includes a new class of the type cis-[Re(CO)2(P−P)(N−N)]+ (where P−P is a chelating diphosphine and N−N is a chelating polypyridine ligand). The four synthetic routes that have been developed rely on either reactive triflate displacement or abstraction of labile chloro ligands, followed by the use of the strong trans-labilizing effect of P donors or direct use of the trans effect of P donors. The spectroscopic, photophysical, and electrochemical properties of these new complexes systematically vary with the net donor ability of the ligands in the coordination sphere, as shown by correlations with Lever's EL parameters. Lifetimes and quantum yields of the bipyridine complexes encompass a broad range, 25−1147 ns and ca. 0.002−0.11, respectively.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
This study explored the effect of radical size, chain length, and mass on the cage recombination efficiency of photochemically generated radical cage pairs. Radical cage pairs containing long-chain radicals of the type [(CpCH(2)CH(2)N(CH(3))C(O)(CH(2))(n)CH(3))(CO)(3)Mo*, *Mo(CO)(3)(CpCH(2)CH(2)(CH(3))NC(O)(CH(2))(n)CH(3))] were generated in hexanes/squalane solution by photolysis (lambda = 546 nm) of the Mo-Mo bonds in (CpCH(2)CH(2)N(CH(3))C(O)(CH(2))(n)CH(3))(2)Mo(2)(CO)(6) (n = 3, 8, 18). The cage recombination efficiencies (denoted as F(cP), where F(cP) = k(cP)/(k(cP) + k(dP)), k(dP) is the diffusion rate constant, and k(cP) is the radical recombination rate constant) for the radical cage pairs were obtained by extracting them from quantum yield measurements for the photoreactions with CCl(4) (a metal-radical trap) as a function of solvent system viscosity. The results show that F(cP) increases as the length of the chain on a radical center increases. This finding likely provides at least one of the reasons why the quantum yields for photolytic polymer degradation (and long-chain molecules, in general) decrease as the polymer chains get longer. In quantitative terms, plots of k(dP)/k(cP) were linearly proportional to mass(1/2)/radius(2), in agreement with the prediction of Noyes' cage effect theory. The "radius" of a long-chain radical, such as those studied herein, is rather vague, and for that reason a less ambiguous structural parameter was sought to replace the r(2) term in the Noyes expression. Plots of k(dP)/k(cP) vs mass(1/2)/surface area suggest that surface area can be used in place of the radius(2) term in the Noyes expression. The significance of being able to use a particle's surface area in the Noyes expression is that the expression becomes useful for nonspherical particles. The new expression allows the approximate prediction of F(cP) values for radicals of different sizes and masses.
A new class of long-lived luminescent complexes of the type cis-ReI(CO)2(N-N)(P-P)+ (where N-N is a chelate polypyridine ligand and P-P is a chelate phosphine) has been prepared. The new Re excited states are of extraordinary stability and exhibit red-shifted spectral responses relative to the well-studied fac-Re(bpy)(CO)3L(+/0) series (L is a variety of neutral and anionic ligands). Of primary interest are their extremely long lifetimes in CH2Cl2 solution, which could be a consequence of an energy gap law different from that of the tricarbonyl complexes.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
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