Poly relaxation parameters

A similar continuity in the Tj s through the melting temperature was previously reported for linear polyethylene. (17) We have now investigated the temperature dependence of this quantity, for this polymer, in more detail and have also studied a low density (branched) polyethylene. The results for the poly-ethylenes are summarized in Fig. 8. The new data reported here substantiate the conclusion previously reached for linear polyethylene. A similar conclusion can now be reached for the baclc-bone carbons of low density (branched) polyethylene. The melting temperature for this particular sample, under the crystallization conditions studied, is less than 110°C. (33) Thus, the spin-lattice relaxation parameters for the bac)cbone carbons are the same for both the linear and branched polymers over the temperature range studied here. Changes that occur in Tq as the temperature is reduced below 0°C involve other considerations and will be discussed in detail elsewhere. (22)... 

Meltzer AD, Tirrell DA, Jones AA, Inglefield PT, Hedstrand DM, Tomalia DA. Chain dynamics in poly(amidoamine) dendrimers a study of carbon-13 NMR relaxation parameters. Macromolecules 1992 25 4541-4548. 

Some of the earliest chemometric NMR analysis of materials involved the PCA of organic peat using C CPMAS NMR spectra,and the analysis of H and C NMR relaxation parameters in coal. Chemometrics and C CPMAS has also been applied to classify soil organic matter. Clayden and co-workers have used FA of the time domain F NMR signal in poly(tetrafluoroethane), PTFE polymers as a method to measure crystallinity. It was demonstrated that the dominant principal component did not correlate well, but that the scores of second and third principal component show an excellent correlation with the PTFE crystallinity. PLS methods have also been used to determine... 

It was shown in section 4.3 that often lengthens significantly for all carbons in isotactic chain segments in dissolved polymers [37]. This may be explained by the RIS analysis in the previous section, given the reasonable assumption that the transitions between conformations is rapid. Furthermore, the analysis shows that the relaxation parameters are insensitive to the rate of the local motions, within this limit. For example, an i-PMMA dyad must have two equally weighted conformations, loosely tg and gt, on symmetry grounds. The calculation described above also finds that tt has a very similar weighting. In contrast, an s-PMMA dyad has only one main conformation, tt, with a smaller contribution from gg. Thus more extensive local motion is to be anticipated in short i-PMMA sequences than in short s-PMMA sequences, in the same overall chain. Similar observations and calculations have been made with poly(acrylonitrile). 

The simulation has been carried out for a poly(2-acrylamido-2-methyl-propanesulfonic acid) (PAMPS) gel that is a fully ionized polyelectrolyte having sulfonic groups as macroions and as counterions. The radius of the polymer chain of PAMPS is r, = 6.08 X 10 m. The other constants used are b = 2.55 X 10 m, = 78 (e = c Cq, where q is the dielectric constant in a vacuum), and T = 300 K. The simulation was carried out for a cubic box with a side length of r (1/2 of a periodic unit cell) and then copied to the whole periodic unit according to the symmetry. The simulation box was divided into 10 x 10 x 10 lattice cells. To make the surface of poly ions on lattice points, r = lOr, was used. Equation 1 was expressed by Poisson s difference equations and the electrostatic potential on lattice points was calculated by Liebmann s method. A relaxation parameter of 0.5 has been used to accelerate the calculation. An iterative difference value of Ae = 10 kT was used to determine the accuracy of the calculation. Symmetric conditions have been used for walls of the simulation box i.e., the normal derivatives of the potential on the walls are zero. 

The inclusion of a variable temperature magic-angle spinning capability for solid state NMR spectroscopy makes feasible the investigation by relaxation parameters of structural and motional features of polymers above and below Tg and in temperature regions of secondary relaxations. Herein, we report variable temperature (50K to 323K) spectral data on semicrystalline poly(propylene) and glassy PMMA. Illustrative of the data are the Tj and results for isotactic... 

A comparison of dielectric and viscoelastic relaxation a process has its own set of difficulties because the viscoelastic processes are small and the parameters and highly temperature dependent. Nevertheless, the data can be analyzed and comparisons made. A comparison of the relaxation parameters for the a processes of poly(vinyl chloride),... 

Berens A (1977) Diffusion and relaxation in glassy polymer powders 1. Fiekian diffusion of vinyl chloride in poly(vinyl choride). Polymer 18(7) 697-704 Berens A, Hopfenberg H (1978) Diffusion and relaxation in glassy polymer powders 2. Separation of diffusion and relaxation parameters. Polymer 19(5) 489-496 Bond DA (2005) Moisture diffusion in a fiber-reinforced composite part 1 - non-Fickian transport and the effect of fiber spatial distribution. J Compos Mater 39(23) 2113-2141 Cai LW, Weitsman Y (1994) Non-Fickian moisture diffusion in polymeric composites. J Compos Mater 28(2) 130-154... 

Addition of 20 mM Mg(II) to poly(I) poly(C) modified some of the 3 P-NMR relaxation parameters (Bolton and James, 1980a). It was found that the internal motion was not affected, but the value increased from 1... 

The non-aqueous system of spherical micelles of poly(styrene)(PS)-poly-(isoprene)(PI) in decane has been investigated by Farago et al. and Kanaya et al. [298,299]. The data were interpreted in terms of corona brush fluctuations that are described by a differential equation formulated by de Gennes for the breathing mode of tethered polymer chains on a surface [300]. A fair description of S(Q,t) with a minimum number of parameters could be achieved. Kanaya et al. [299] extended the investigation to a concentrated (30%, PI volume fraction) PS-PI micelle system and found a significant slowing down of the relaxation. The latter is explained by a reduction of osmotic compressibihty in the corona due to chain overlap. 

Table 18. Values of correlation parameter g, relaxation time tJ.p and activation energy EJ p of a relaxation process of dipole polarization for some comb-like poly(methacrylates) in toluene solutions...

The dilatational rheology of the poly(vinylacetate) monolayer onto an aqueous subphase has been studied between 1°C and 25°C by Monroy et al. [59], These authors have used the combination of several techniques. By this way, the exploration of a broad frequency range was possible. The relaxation experiments have shown multiexponential decay curves, whose complexity increases with decreasing the temperature. A regularization technique has been used to obtain the relaxation spectra from the relaxation curves and the dilatational viscoelastic parameters have been calculated from the spectra. The shapes of the relaxation spectra agree with the predictions of the theoretical model proposed by Noskov [100],... 

Not all of these parameters provide information in a direct manner nonetheless, the inferred information is important in characterizing motional frequencies and amplitudes in macromolecules. Fundamental to this characterization is the measurement of relaxation data over a range of temperature. As an example, we report in this section very preliminary results on the Ti and Tip behavior for the carbons in a 90% isotactic, 70% crystalline sample of poly(propylene), PP. 

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