High-pressure phases in polymers. I. Spherulitic growth kinetics in cis-polyisoprene

This is the first paper in a series dealing with the crystallization of high polymers at elevated pressures. Through an extension of the thin-film technique using osmium tetroxide staining, the measurement of lamellar growth kinetics at high pressures as well as the observation of micromorphological changes has proved possible. Three different morphological species of cis-polyisoprene have been detected in the pressure–temperature plane. A review is given of the conditions governing their formation and the growth kinetics of lamellar crystals are discussed in detail. Secondary nucleation theory is obeyed, the major effect of pressure being to alter the kinetics through the thermodynamic transitions. Variations in lamellar thickness with pressure may be explained simply in terms of the elevation by pressure of the equilibrium melting point.     

The preparation,polymerization and copolymerization of (η5-vinylcyclopentadienyl)dicarbonylnitrosylchromium, (η5-C5H4CHCH2)Cr(CO)2NO

The first report on the preparation, polymerization, and copolymerization of a nitrosyl-containing vinylcyclopentadienylmetal monomer, (η⁵-C₅H₄CHCH₂)-Cr(CO)₂NO, is described. (η⁵-Vinylcyclopentadienyl)-dicarbonylnitrosylchromium (A) was prepared in good yield by the acylation of η⁵-cyclopentadienyl-carbonylnitrosylchromium followed by sodium borohydride reduction of the keto function and acid-catalyzed dehydration. Monomer A homopolymerizes and copolymerizes with styrene, N-vinylpyrrolidone, and vinyl cymantrene in the presence of azo initiators. Reactivity ratios in the copolymerization of A with styrene were r₁ = 0.30 and r₂ = 0.82 from which the value of e for A was found to be ?1.98. Thus, A is an exceptionally electron-rich monomer.     

μ-Fluoro complexes peroxydes du molybdene VI

On a mis en évidence un pont Mo-F-Mo dans des oxoperoxomolybdates VI complexes de coordinence sept de formule M^I{Mo₂O₂(O-O)₂(dipic)₂F}; M^I = {(C₂H₅)₄N}⁺, {(CH₃)₄N}⁺, Cs⁺, Rb⁺, K⁺, Na⁺ -(dipic) = {C₇H₃NO₄}^2-. L'ion est mononucléaire pour M^I = NH⁺₄ et si le ligand halogéno eset Cl.     

A novel synthesis of 1,4-diarylpiperazines

1,4-Diarylpiperazines are readily prepared, generally in good yields, by the reaction of substituted aromatic amines with two thirds of an equivalent of tris(2-chloroethyl)phosphate.     

Permutational symmetry of reduced density matrices

The problems of permutational symmetry of the density matrices in reduction are studied. Some necessary and sufficient conditions for N, [λ₁], [λ₂]-derivability problem are given.     

Cyanopolyesters

The reaction of alkyl acyl cyanides with electron-rich aromatic substrates in highly acidic media was found to give high yields of bisadducts. Reactions with phenol produced two new eyanobisphenols which readily underwent polycondensation with acid chlorides. The resultant polyesters can be directly compared to the polyesters of bisphenol-A (BPA) strictly on the basis of polar effects since steric differences are nominal. Thermal, mechanical, electrical and solubility characteristics are reported for the cyanopolycarbonates, which show higher thermal transitions and thermal stability than BPA polycarbonate.     

Differential entropy and tiling

This paper relates the differential entropy of a sufficiently nice probability density functionp on Euclideann-space to the problem of tilingn-space by the translates of a given compact symmetric convex setS with nonempty interior. The relationship occurs via the concept of the epsilon entropy ofn-space under the norm induced byS, with probability induced byp. An expression is obtained for this entropy as approaches 0, which equals the differential entropy ofp, plusn times the logarithm of 2/, plus the logarithm of the reciprocal of the volume ofS, plus a constantC(S) depending only onS, plus a term approaching zero with. The constantC(S) is called the entropic packing constant ofS; the main results of the paper concern this constant. It is shown thatC(S) is between 0 and 1; furthermore,C(S) is zero if and only if translates ofS tile all ofn-space.This paper presents the results of one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract No. NAS 7-100, sponsored by the National Aeronautics and Space Administration.     

Spectral detection of terminal ring quinones

Terminal ring quinones can be detected specifically by a simple spectroscopie method involving reaction of the quinone with quinaldinium or lepidinium salts in alkaline solution. Other types of quinones and carbonyl derivatives have given negative results. 3-Ethylrhodanine can also be used as a reagent, especially for terminal ring p-quinones. All of these colorimetric procedures are amenable to quantitation.     

Topographic organization of Hebbian neural connections by synchronous wave activity

Experimental studies have revealed that the refinement of early, imprecise connections in the developing visual system involves activity in the retina before the onset of vision. We study the evolution of initially random unidirectional connections between two excitable layers of FitzHugh-Nagumo neurons with simulated spontaneous activity in the input layer. Lateral coupling within the layers yields synchronous neural wave activity that serves as a template for the Hebbian learning process, which establishes topographically precise interlayer connections. (c) 2001 American Institute of Physics.