Relaxation Of Poly Research Articles

The β dielectric relaxation in some methacrylate polymers

AbstractDielectric results at frequencies between 6 × 10−4 and 105 Hz are given for the β relaxation region of poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), poly(butyl methacrylate) (PBMA), and poly(isobutyl methacrylate) (PisoBMA). Apparent activation energies and relaxation strengths are calculated, as well as the relaxation time distribution and the form factor of the Fuoss‐Kirkwood equation. It is found that in PMMA, PEMA, and PBMA, the activation energy of the β relaxation is the same, the maxima occurring at the same frequency for the same temperatures, in accordance with the dynamic mechanical results of Heijboer, the dielectric results of Mikhailov, and at variance with data of Tetsutani et al. It is also found that the form factor follows the same temperature dependence. Data on the β relaxation of poly(hydroxyethyl methacrylate) (PHEMA), not previously reported, are also presented, and the displacement toward high temperatures of the β relaxation of PisoBMA and PHEMA is justified.

Poly(ADP-ribosyl)ation of chromatin: kinetics of relaxation and its effect on chromatin solubility.

We have studied the kinetics of relaxation of poly(ADP-ribosyl)ated polynucleosomes produced by endogenous enzyme activity by comparing the generation of hyper(ADP-ribosyl)ated histone H1 and its effect on the chromatin structure as revealed by electron microscopy. A correlation can be established between the appearance of histone H1 modified forms and the localized relaxation of the chromatin. We have also noticed, in parallel, that poly(ADP-ribosyl)ated chromatin showed increased solubility in the presence of Mg2+ and 0.2 M NaCl. Electron microscopic examination of the solubilized chromatin produced by poly(ADP-ribosyl)ation shows polynucleosomes exhibiting more relaxed conformation, whereas an increasing amount of hyper(ADP-ribosyl)ated histone H1 is found in the pellet, as shown by acid-urea-polyacrylamide electrophoretic separation of histone extracts.

Spin probe study of relaxation in poly(oxytetramethylene)

AbstractUsing the spin probe method, the rotational mobility of two probes in poly(oxytetramethylene) (POT) in the region of rapid and slow rotation was investigated. Based on the relaxation diagram the obtained ESR results are compared and discussed in connection with other literature data. It was found that the behaviour of the probes corresponds to the α + β relaxation in the range of high frequencies. Differences in mobility of the probes as well as anisotropy effects of rotations are also discussed.

Pulsed NMR study of proton and fluorine-19 spin-lattice relaxation and cross relaxation in poly(vinylidene fluoride)

Mesure du temps de relaxation de la phase alpha entre 150 et 400°K. Simulation par un modele qui comprend les interactions dipolaires homonucleaires et heteronucleaires et une contribution paramagnetique a la relaxation nucleaire

Low‐temperature dielectric relaxation in poly(4,4′‐oxydiphenylene pyromellitimide)

AbstractThe effect of end groups on the low‐temperature dielectric relaxation in poly(4,4′‐oxydiphenylene pyromellitimide) has been studied using three kinds of samples with different content of anhydride end groups. The magnitude of the dielectric loss peak, designated here the V peak, which appears near −40°C at 1 kHz, depends on the content of anhydride end groups. If a sample with few anhydride end groups is allowed to absorb water, a loss peak appears near the temperature region of the V peak, but it disappears after subsequent heating. In contrast, a sample having a larger amount of anhydride end groups exhibits a large V peak which remains even after further heating. We conclude that the Oportion of the anhydride end groups is responsible for the V peak, though there may be an additional contribution from absorbed water.

Relaxation spectroscopy of poly(vinylidene fluoride)

Abstract The relaxation spectra and their temperature dependence for the four relaxation processes in poly(vinylidene fluoride) found in the temperature range from −180°C to 130°C are determined by using stress relaxation measurement and complementary dielectric loss measurement. These relaxations are designated as α M , β, γ1 and γ2 in the order of descending temperature. A comparative study of the characteristics of the relaxations in poly(vinylidene fluoride) and poly(ethylene) shows that these relaxations in poly(vinylidene fluoride) correspond to the α2-, β-, γ1-and γ2-relaxations in poly(ethylene) respectively. Further, a slight loss process is found in poly(vinylidene fluoride) in the temperature range between the α M -region and the β-region and it is thought to correspond to the α1-relaxation in poly(ethylene). The temperature dependence of relaxation times for the β-relaxation is expressed by WLF equation and the glass transition temperature is estimated to be ca. −42°C.

Dielectric relaxation in poly(ethylene oxide) complexed with alkali metal perchlorates

Audio frequency complex admittance measurements over the temperature range 5.5–350 K have been performed on poly(ethylene oxide) (PEO) complexed with lithium and sodium perchlorates. No evidence of an α a relaxation was seen in any sample. In the Li-complexed material, the γ relaxation occurs at about 174 K and 1000 Hz which is the same as for pure PEO. In the Na-complexed materials, there appear to be more than one peak in this region, and the relative peak heights are concentration dependent. The result is that at the 8:1 doping level, there is a broad, skewed relaxation whose peak occurs at about 203 K and 1000 Hz, while at 4.5:1 NaClO 4 the relaxation appears much closer to a normal peak with a maximum at 185 K for the 1000 Hz data. Combined with previous results for thiocyanate complexed PEO, these results show that distortions in the polymer chain depend on both the cation and anion. Next, two new relaxations are observed at low temperatures. The first, occuring at 60–100 K is very weak and is common to all PEO samples. The second occuring at very low temperatures, is only found for perchlorate complexed PEO and is attributed to the localized motion of perchlorate-induced defects on the exterior of the chains. The high temperature electrical conductivity for PEO 8:NaClO 4 is found to be larger than PEO 4.5:NaClO 4 in agreement with the trend observed by other workers for PEO complexed with different alkali metal salts.

Diffusion of alcohols and relaxation in poly(methyl methacrylate): effect of thermal history

The sorption behavior of alkyl alcohols in poly(methyl methacrylate) is analyzed after predetermined annealing treatments of the polymer matrix. Weight uptake, penetration depth and sample dimensions are reported versus time. Dimensionless parameters are used, through which master curves are obtained for both weight uptake and the area perpendicular to the main penetration direction. Contrary to what is observed in polystyrene—n-alkane systems, in the present case either the specific plasticization of the penetrant must be accounted for, or a non-localized swelling model must be used to explain the behavior.

Effects of paramagnetics on proton spin relaxation in poly(p-phenylene)

Measurements of T 1 e for protons in poly( p-phenylene) indicate that relaxation is dominated by direct interaction with paramagnetic centers. Processes to remove paramagnetic centers decrease the number of centers, but the process cannot be carried to completion. Temperature-dependent relaxation measurements give an activation energy of 4.2 kJ mol −1 for the process which modulates the direct electron-nuclear dipole-dipole interaction.

NMR relaxation in poly(butylene terephthalate) and poly(butylene terephthalate) containing segmented copolymers. 5

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTNMR relaxation in poly(butylene terephthalate) and poly(butylene terephthalate) containing segmented copolymers. 5Lynn W. Jelinski, Joseph J. Dumais, P. I. Watnick, M. D. Sefcik, A. Engel, and M. D. SefcikCite this: Macromolecules 1983, 16, 3, 409–415Publication Date (Print):March 1, 1983Publication History Published online1 May 2002Published inissue 1 March 1983https://doi.org/10.1021/ma00237a014RIGHTS & PERMISSIONSArticle Views92Altmetric-Citations20LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Dielectric relaxation in poly(2-ethynylnaphtalene) determined by thermally stimulated depolarization currents

The thermally stimulated depolarization currents from poly(2-ethynylnaphtalene) with cis-cisoidal and transcisoidal structures were studied over the temperature range 200–380 K. The single peak ρ of the cis-cisoidal isomer was assigned to the Maxwell-Wagner polarization. The β1 and β2 peaks of the trans-cisoidal isomer arise from a single dipolar relaxation process and respectively from a dipolar relaxation distributed in natural frequency. Certains assignements are based on comparative work on polyphenylacetylene.

Ultrasonic relaxation of poly(N-vinylpyrrolidone) and dextran in aqueous solution

The ultrasonic relaxation spectra of the polymers dextran and poly(N-vinylpyrrolidone) have been studied in aqueous solution over the frequency range 1–100 MHz. A range of molecular weights and concentrations were used to span dilute and semi-dilute solution conditions (0.44 < c[η] < 11). The results indicate that the relaxation spectra can be resolved into two components, one associated with the viscoelastic normal mode of the polymer chain and the other a significant contribution associated with more local conformational changes within chain segments.

Anomalous dielectric relaxation in poly(dimethyl siloxane) polymers

The dielectric relaxation in poly(dimethylsiloxane) of viscosity 10 5 CSt at around the melting point is found to deviate from the existing theory. Although the position of maximum loss is insensitive to changes in temperature in the range −40°C to −54°C, the magnitude of the loss changes by about 50%.

Effects of thermal history, crystallinity, and solvent on the transitions and relaxations in poly(bisphenol‐A carbonate)

AbstractThe following system of nomenclature for the transitions and relaxations in polycarbonate has been proposed: α = Tg = 150, β = 70, γ = −100, and δ = −220°C (frequency range of 10–50 Hz). The three component peaks of the γ relaxation are denoted by γ1, γ2, and γ3 relaxations correspond to phenylene, coupled phenylene‐carbonate, and carbonate motions, respectively. Dynamic mechanical analysis of poly(bisphenol‐A carbonate) using the DuPont 981–990 DMA system shows that the magnitude of the β relaxation depends upon the thermal history of the polycarbonate; annealing greatly reduces the intensity of the β relaxation. A relaxation map constructed for the β relaxation gives an activation energy of 46 kcal/mol. Exposure of polycarbonate to methylene chloride vapor for various times shows that after an induction period of about 5 min the intensity of the γ3 relaxation at −78°C decreases whereas the intensity of the γ1 relaxation of −30°C is unaffected and the ratio E″(γ1)/E″(γ3) increases linearly with the square root of time. This has been ascribed to the interaction of methylene chloride on the carbonate group in polycarbonate. Thermal crystallization of polycarbonate does not affect the positions of the γ relaxation and the glass transition peaks, but merely reduces their intensity. The glass transition peak intensity falls off sharply in comparison to the γ relaxation intensity. Both the γ3 and γ1 peaks in polycarbonate have been observed simultaneously for the first time by dynamic mechanical analysis. Impact strength measurements show that methylene chloride treatment of polycarbonate results in a change in mode of failure from ductile to brittle with a resultant 40‐fold reduction in impact energy for fracture. Thermally crystallized polycarbonate exhibits brittle fracture with very low force and energy at break.

Deuteration shift of low temperature dielectric relaxations

Polyethylene and paraffin samples at a temperature of 4.2 K exhibited dielectric relaxations as a result of containing v arious phenol derivatives and amines. Four of these dipolar additives caused distinctly faster relaxations in poly(C 2D 4) than in comparable poly(C 2H 4), the difference being 13 to 20%. The amines, like the phenol derivatives reported earlier, also relaxed orders of magnitude more slowly when their labile hydrogens had been deuterium-substituted. A 4-methyl-2, 6-di-tert-butyl phenol sample in which most of the non-labile hydrogens were deuteriums, relaxed more slowly than the normal compound, the relaxation time being 25–30% longer. These results are all explained with the phononassisted tunnelling model and provide new evidence for the validity of this model.

Piezoelectric relaxation in poly(γ‐methyl‐L‐glutamate) at high temperature

AbstractPiezoelectric relaxation has been studied on elongated poly(γ‐methyl‐L‐glutamate) films with the α‐helical molecular conformation. Relaxation processes are observed near 0 and 100°C. Each process has a dual character composed of relaxational and retardational frequency dependences. The low‐temperature process is ascribed to thermal motion of side chains. The high‐temperature process, discussed in relation to the dielectric relaxation, is attributed to the ionic dc conduction connected with the two‐phase structure of crystalline regions and the electrode polarization.

Transitions and Relaxations in Poly(trifluoroethylene)

Transition behavior in poly(trifluoroethylene)(P3FE) was studied (1) by mechanical-relaxation measurements, dealing with the influence of crystallinity, molecular weight, cold drawing, and copolymerization with vinylidene fluoride, and (2) by dielectric-relaxation measurement at various frequencies up to 300 kHz. In P3FE, two transitions have been observed with peaks at 50°C (designated α) and −20°C (designated β) by mechanical-relaxation measurement at 35 Hz. It was found that the α-transition was related to micro-Brownian motion of main chain in the amorphous region, and the β-transition was related to local molecular motion in both the amorphous and crystalline regions.

Dielectric γ relaxation in poly(2‐hydroxyethyl methacrylate)

AbstractThe dielectric constant and loss were measured for poly(2‐hydroxyethyl methacrylate) from −90 to 34°C over the frequency range 30 to 3 × 105 Hz in the γ relaxation region. The relaxation was also characterized using activation energies.

13C n.m.r. study of optically active polymers: 2. Relaxations in poly [(S)-4-methyl-1-hexene

T 1, T 2 and NOE were measured in 13C n.m.r. spectra of two fractions of poly [(S)-4-methyl-1-hexene] obtained by selective solvent extraction (diethyl ether and cyclohexane) of the polymers prepared in the presence of isospecific catalysts. T 1 measurements provide evidence in the two fractions for the existence of different conformational weightings about side chain bonds according to conclusions from vibrational spectroscopy studies. Subtle configurational differences of the two substantially isotactic samples are suggested to explain this result. A discussion of the dynamic parameters related to the correlation time is also presented which supports the above explanation.

Methyl group tunneling and viscoelastic relaxation in poly(α‐methyl styrene)

Methyl group tunneling and viscoelastic relaxation in poly(α‐methyl styrene)