Search results for "Glass transition"

Single Particle Motion of Hard-Sphere-Like Polymer Micronetwork Colloids Up to the Colloid Glass Transition

1997

Polymer micronetwork spheres swollen in a good solvent can be regarded as colloids which require no special stabilisation to avoid aggregation. Their interactions can be timed by changing the degree of internal crosslinking. The phase behaviour and the static structure factor demonstrate that crosslink density of 1:10 (inverse number of monomer units between crosslinks) is sufficient to achieve hard sphere behaviour. We designed a host-tracer system consisting of core-shell micronetwork spheres (core: polystyrene; shell: poly-t-butylacrylate) in a host of refractive-indexmatched poly-t-butylacrylate micronetwork colloids. Employing a crosslink density of 1:10 and tuning the polydispersity s…

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…

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…

1991

Prediction of Indices of Refraction and Glass Transition Temperatures of Linear Polymers by Using Graph Theoretical Indices

2002

Graph theoretical indices were exclusively used in the prediction of indices of refraction, n, and glass transition temperatures, Tg, into a group of addition polymers. Models with 10 variables were selected for the prediction of n (r = 0.981, SEE = 0.0147) and Tg/M (r = 0.946, SEE = 0.439). The average errors in the predictions were 0.69% and 12.7% for n and Tg, respectively. The descriptors involved in these models were calculated from the structures of the monomers.

Temperature dependence of the static structure factor of ortho-terphenyl in the supercooled liquid regime close to the glass transition

1993

Abstract Studying the temperature dependence of the static structure factor of ortho-terphenyl from the liquid state down to the glass we find that the main peak of S ( Q ) is split into two maxima which behave quite differently. While the maximum at Q =1.4 A −1 is not much affected by the temperature variation the one at 1.9 A −1 is significantly enhanced. This effect is connected with a change of the short range order, i.e. of the intermolecular distances, but evolves continuously. Thus the dynamic anomalies that have been observed in this system around a characteristic temperature T c ≈290 K are not simply due to a discontinuous change in S ( Q ) but can be attributed to the existence of…

1992