Phase state and molecular mobility of segmented polyurethanes

Spin-lattice and spin-spin NMR relaxation was studied in a series of segmented polyurethanes based on poly(diethylene glycol adipate), 2,4-tolylene diamine, and 2,4-toluene diisocyanate. It was concluded that NMR relaxation is determined by physical interactions between rigid blocks and also between rigid and flexible blocks. The dependence of the degree of segregation on the molecular weights of rigid and flexible blocks was determined. A quite high degree of segregation in the investigated systems and the related manifestations of individual features of flexible blocks allowed us to follow the dynamics of the molecular chain with fixed end and study variation of the glass transition temperature and the activation energy of the segmental motion of this chain as a function of its molecular weight

Phase state and molecular mobility of segmented polyurethanes

Spin-lattice and spin-spin NMR relaxation was studied in a series of segmented polyurethanes based on poly(diethylene glycol adipate), 2,4-tolylene diamine, and 2,4-toluene diisocyanate. It was concluded that NMR relaxation is determined by physical interactions between rigid blocks and also between rigid and flexible blocks. The dependence of the degree of segregation on the molecular weights of rigid and flexible blocks was determined. A quite high degree of segregation in the investigated systems and the related manifestations of individual features of flexible blocks enabled to follow the dynamics of the molecular chain with fixed end and study variation of the glass transition temperature and the activation energy of the segmental motion of this chain as a function of its molecular weight

Dipole-Echo Formation in Three-Pulse-Sequence NMR Experiments on Polymer Systems

Data from three-pulse NMR experiments, namely, the Goldman-Shen pulse sequence and the stimulated-echo sequence, on partially crystallized poly(ethylene glycol) and tetrafunctional dimethylsiloxane networks are presented. A dipole echo has been observed after a third radiofrequency pulse. Quantum mechanical calculations of the response of the spin system to the three-pulse sequences have been performed, considering only thez-zcomponent of the dipole-dipole spin coupling. The resulting expression suggests dipole-echo formation and is in agreement with experimental data. © 1995

System of active regulation of the temperature and temperature gradient in nuclear magnetic resonance sensors

An active system of temperature regulation and temperature gradient in a sample on the example NMR sensor is described in this work. By supporting the given average temperature, the system of temperature-stabilization allows one to set and supervise the size and direction of the temperature gradient along a sample. The temperature of a sample is maintained with on accuracy of about ±0.1°C in a temperature interval of-150 to +200°C with a longitudinal temperature gradient no more than ±0.2°C. The value of the temperature gradient is established in the range of 0° to 10°C/cm in both directions. © 1998 MAHK Hayka/Interperiodica Publishing

Pulsed 1H NMR study of the effects of the rigid block content on the phase state of segmented polyurethanes

The effect of the content of rigid blocks on the phase state and structure of rigid domains in segmented polyurethane based on polyethylenebutyleneglycol adipate, 1,4-butandiol, and 4,4′-diphenylmethane diisocyanate is studied with the aid of pulsed 1H NMR. It is shown from an analysis of free induction decays and using the Goldman-Shen technique that in the specimen having the minimum rigid block length a microphase is formed whose domains have sharp boundaries without intermediate regions. With increase in rigid block length, a second type of domain appears together with the first, consisting of a central part and an intermediate region of high molecular mobility. The ratio of the number of domains of different types depends on the temperature. The dimensions of the domains and intermediate regions are evaluated, and possible structural models are considered. © 1989

System of active regulation of the temperature and temperature gradient in nuclear magnetic resonance sensors

An active system of temperature regulation and temperature gradient in a sample on the example NMR sensor is described in this work. By supporting the given average temperature, the system of temperature-stabilization allows one to set and supervise the size and direction of the temperature gradient along a sample. The temperature of a sample is maintained with on accuracy of about ±0.1°C in a temperature interval of -150 to +200°C with a longitudinal temperature gradient no more than ±0.2°C. The value of the temperature gradient is established in the range of 0° to 10°C/cm in both directions

Dynamic and structural properties of oxyethylated isononylphenols

© 2016Diffusion coefficients, dielectric relaxation times and refraction coefficients were measured, and activation energies of translational and rotational mobilities were determined for a series of oxyethylated phenols (neonols AF9-n) p-C9H19C6H4-O(CH2CH2O)nH, n = 4, 6, 8, 9, 10, 12, at different temperatures. The results demonstrated the existence of contraction and transition phenomena that changed the structure of neonol molecules at n ∼ 9 from a zigzag to a meander form

Specifics of the physicochemical properties of tetramethylurea

The rotational and translational mobility of tetramethylurea molecules over the temperature range 15-60°C was studied using the NMR relaxation and proton spin-echo methods. The activation energies for these motions were calculated. The density, viscosity, isothermal compressibility, and cubic expansivity were determined. A thermogravimetric analysis of the substance was performed. The physicochemical properties of tetramethylurea were compared to those of urea, its other methyl-substituted derivatives, and dimethylformamide. Copyright © 2005 by Pleiades Publishing, Inc