Search results for " transition"

RELAXATION METHODS FOR STUDYING MACROMOLECULAR MOTION IN THE BULK

1982

Abstract Macromolecular motion in amorphous and partially crystalline polymers is discussed in the light of recent relaxation experiments with particular emphasis on NMR methods. Polystyrene and polyethylene serve as pertinent examples where a considerable amount of new experimental data provides a bysis for better understanding molecular processes below and above the glass transition, and in the melt.

Synthesis, optical, and thermal properties of glassy trityl group containing luminescent derivatives of 2-tert-butyl-6-methyl-4H-pyran-4-one

2012

In this work we present simple preparation of original trityl group containing glassy luminescent 6-styryl substituted derivatives of 2-(2-tert-butyl-4H-pyran-4-ylidene)malononitrile (DWK-1TB), 2-(2-tert-butyl-4H-pyran-4-ylidene)-2- ethyl-2-cyanoacetate (KWK-1TB), 2-(2-tert-butyl-4H-pyran-4-ylidene)-1H-indene-1,3(2H)-dione (ZWK-1TB) and 5-(2-tert-butyl-4H-pyran-4-ylidene)pyrimidine-2,4,6(1H,3H,5H)-trione (JWK-1TB). Their optical properties have been investigated. The absorption maxima of synthesized glasses is in region from 425 nm to 515 nm and emission maxima is from 470 nm to 625 nm in solution of dichloromethane. But absorption maxima of their solid films is from 425 nm to 500 nm and em…

Über die polymerisation bei der sublimation des trioxans. 17. Mitt. Über polyoxymethylene

1962

Bei der Sublimation von gereinigtem Trioxan und bei seiner Kristallisation aus der Schmelze erfolgt in der kristallinen Phase eine langsame Polymerisation zu hochmolekularem Polyoxymethylen. Die Ausbeuten an Polymeren sind um so hoher, je trockener das Trioxan ist und je geringer der Fremdgasdruck bei der Sublimation ist. Es wurde festgestellt, das diese Polymerisation durch Spuren von monomerem Formaldehyd ausgelost wird; wenn letzterer durch Silberoxyd zerstort wird, kann Trioxan unverandert sublimiert und kristallisiert werden. Wahrend der Polymerisation wird monomerer Formaldehyd von den wachsenden Polyoxymethylenketten abgespalten und so der Polymerisationskatalysator regeneriert. Desh…

Thermal and optical properties of 4H-pyran-4-ylidene fragment and bis-styryl and triphenyl groups containing derivatives

2014

Small D-π-A type organic molecules with incorporated 4H-pyan-4-ylidene (pyranylidene) fragment in their structures show potential in organic photonics - such as materials for organic light emitting diode application studies and organic solid state lasers. Additional incorporation of bulky triphenyl- groups in their structures gives them the ability to form thin amorphous solid films from volatile non-polar organic solvents. Unfortunately, there is still no clear relation between compound organic structures and their thermal and optical properties. In order to investigate the above mentioned regularities we have synthesized a series of tripheyl- group containing derivates of 2,6-bis-styryl-4…

1986

A procedure is described for the preparation of a block copolymer with A-B-A sequences in which ω-ω′-dihydroxy-poly-(ethylene glycol) is inserted between two polymeric monoacidic chains of polycaproamide and bonded to them by means of ester links. The resulting material was characterized. The copolymer is isomorphous with the polycaproamide. Thermal treatments induce a crystalline transition γ α as in polycaproamide. The influence of the moisture content on the glass transition temperature and on the storage modulus is discussed. Ein Verfahren zur Herstellung eines Blockcopolymers mit A-B-A-Sequenzen wird beschrieben. In dem Copolymer ist ω-ω′-Dihydroxy-polyethylenglycol uber Esterbindungen…

Deuteron Magnetic Resonance Study of Order and Dynamics in Liquid Crystal Polymers

1984

Abstract Thermotropic nematic polyesters, specifically deuterated at different positions of the polymer chain are studied by multiple pulse dynamic NMR. Analysis of the NMR experiments is achieved, employing a comprehensive model, based on the stochastic Liouville equation. Computer simulations provide the orientational distributions and conformations of the polymer chains and the correlation times of the various motions. In the anisotropic melt the correlation times for chain reorientation and trans-gauche-isomerization are in the range of 0.1–10 ns. Decreasing the temperature of the solid polymer first freezes the intermolecular motions. Thus, below the glass transition only intramolecula…

Theoretical and Spectroscopic Studies On Imino-carbon Palladated Pyridine-2-carbaldimines

1987

Abstract Ab initio LCAO-MO-SCF calculations on the model compounds C 5 H 4 N-2-C(R 1 )=NH [R 1 = H ( 2c ) and R 1 = trans -PdCl(PH 3 ) 2 ( 4c )] indicate that the E - trans conformation is favored over the E - cis one by 16.9 kJ mol −1 for 2c and by 25.0 kJ mol −1 for 4c . One of the factors which stabilizes the E-trans arrangement for 4c is a weak bonding interaction between the palladium center and the pyridine nitrogen. On going from 2c to 4c a slight charge enrichment on the pyridine carbons and a more pronounced one on the nitrogen atoms is computed, whereas the charge density of the imino carbon atom is decreased. In 4c no π contribution to the PdC bond is observed. Protonation of th…

Spin transition in heptanuclear star-shaped iron(III)–antimony(V) NCS- and CN-bridged compounds

2009

Abstract The precursor [FeIII(L)Cl] (LH2 = N,N′-bis(2′-hydroxy-benzyliden)-1,6-diamino-3-azahexane) has been prepared and Mossbauer spectroscopy assigned a high-spin (S = 5/2) state at room temperature. The precursor is combined with the bridging units [SbV(X)6]− (X = CN−, NCS−) to yield star-shaped heptanuclear clusters [(LFeIII–X)6SbV]Cl5. The star-shaped compounds are in general high-spin systems at room temperature. On cooling to 20 K some of the iron(III) centers switch to the low-spin state as indicated by Mossbauer spectroscopy, i.e. multiple electronic transitions. While the cyano-bridged complex performs a multiple spin transition the thiocyanate-compound shows no significant popul…

Oxygen Radical Scavengers

2010

The myocardium can tolerate only relatively short periods of total myocardial ischemia without myocardial cell death. Following short ischemic periods, ischemic damage is reversible by reperfusion. However, with increasing duration and severity of ischemia, the damage inflicted to cardiomyocytes following reperfusion becomes irreversible. The combined pathologic events in the myocardium that follow a critical period of ischemia and leading to either reversible or irreversible damage to both cardiomyocytes and cardiac microvasculature is known as ischemia-reperfusion injury (Goldhaber and Weiss 1992).

Absorption spectrum of the f(A1g) ← X(Eg), a(F2g) electronic transition of OsF6

1997

Abstract The absorption spectrum of the visible band of OsF 6 has been recorded using a commercial spectrophotometer. The first vibronic assignments for this band have been realized using the analogy with the d ← X transition of IrF 6 . Some vibronic parameter values are derived.