ABSTRACT
Carbonyl adducts to CuMCl(4) (M = Al and Ga) have been characterized by single-crystal and/or powder X-ray diffraction, IR and diffuse reflectance UV/vis spectroscopy. Up to two equivalents of carbon monoxide ( approximately 200 cm(3)/g relative to stp) are sorbed at room temperature, with equilibrium binding pressures of below 0.5 atm of CO. The carbonyl bonding is shown to be nonclassical, implicating the dominance of sigma-bonding and absence of pi-back-bonding. Analysis of the crystalline structures of the parent and adduct phases provides an atomistic picture of the sorptive reconstruction reaction. Comparison of the reactivity of CO and ethylene with these CuMCl(4) materials, as well as other copper(I) halide compounds that exhibit classical and nonclassical modes of bonding, demonstrates the ability to tune the reactivity of the crystalline frameworks with selectivity for carbon monoxide or olefins, respectively.
ABSTRACT
A new helically pillared and chiral solid, Cu(pzc)2AgReO4 (I, pzc = pyrazinecarboxylate), was synthesized from hydrothermal reactions at 95-125 degrees C. The structural origin of its chirality, relative to the achiral M(pzc)2(H2O)2AgReO4 (II, M = Co; III, M = Ni) analogues, arises from significantly tilted pillars and hydrogen bonds to the AgReO4 layers. The new pillared structure exhibits second harmonic generation activity, CO2 absorption, thermal stability to approximately 250 degrees C, and Curie-Weiss magnetism expected for isolated Cu2+.
ABSTRACT
Thermoplastic elastomer gels (TPEGs), molecular networks composed of a microphase-separated multiblock copolymer swollen to a large extent by a low-volatility midblock-selective solvent, are ubiquitous in a wide range of contemporary technologies, including home and office products, athletic equipment, and telecommunications devices. In this work, we investigate the effect of several network-forming nanoscale modifiers-two different silica nanoparticles, three different nanoclays, and a multiwalled carbon nanotube-on the property and morphology development of a TPEG prepared from a microphase-ordered poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) triblock copolymer imbibed with an EB-compatible aliphatic mineral oil. Dynamic rheological measurements of the resultant nanocomposite TPEGs confirm that addition of these modifiers affects the linear viscoelastic threshold and increases, to different extents, the dynamic elastic modulus, the dynamic yield stress, and the maximum operating temperature of the parent TPEG. X-ray diffraction analysis reveals that the nanoclays used to generate three series of modified TPEGs are generally swollen with copolymer and/or solvent.
ABSTRACT
Using chiral catalysts of (R)- and/or (S)-BINOL-Ti, the asymmetrical polymerization of achiral monomer, N-(1-anthryl)-N'-n-octadecylcarbodiimide, yielded soluble nonregioregular polyguanidines of Poly-R1 and Poly-S1. A racemization process occurred when the toluene solution of Poly-R1 was annealed at elevated temperatures (70-80 degrees C). Kinetic studies reveal this to be a slow process with an activation energy of ca. 36 kcal/mol. On the other hand, using titanium(IV) trifluoroethoxide catalyst, the polymerization of N-(1-anthryl)-N'-[(R)- and/or (S)-3,7-dimethyloctyl]carbodiimides afforded highly regioregular polyguanidines of Poly-R2 and Poly-S2. These polymers adopt stable helices in various solvents and elevated temperatures, whose kinetically controlled conformations and thermodynamically controlled conformations are essentially the same.
