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  • Articles  (125)
  • microwaves  (72)
  • glass transition  (53)
  • Wiley-Blackwell  (125)
  • American Chemical Society
  • Molecular Diversity Preservation International
  • Physics  (125)
  • 1
    Electronic Resource
    Electronic Resource
    Depolarization thermocurrent studies in poly(hydroxyethyl acrylate)/water hydrogels (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 1001-1008 
    Details
    ISSN: 0887-6266
    Keywords: hydrogels ; water in poly(hydroxyethyl acrylate) ; dielectric relaxation ; thermally stimulated depolarization currents (TSDC) ; glass transition ; space charge polarization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Detailed investigations on the dielectric relaxation mechanisms in poly(hydroxyethyl acrylate) (PHEA), by means of the thermally stimulated depolarization currents (TSDC) method in the temperature range 77-300 K are reported. There is particular interest in the dependence of the dielectric relaxation mechanisms on the water content h, h = 0 - 0.5 w/w, in an attempt to contribute to a better understanding of the physical structure of water in the PHEA hydrogels. We employ thermal sampling (TS) and partial heating (PH) techniques to experimentally analyze the observed complex relaxation processes, due to the secondary (βsw) and the main (α) relaxation, into approximately single responses and to determine the spectra of activation energies E(T) at different h values. Measurements with different electrode configurations reveal different aspects of the dynamics of the relaxation mechanisms and allow the distinction between dipolar and conductivity relaxation contributions. It is shown that by means of these techniques we can determine certain temperature characteristics for the α relaxation and investigate their dependence on water content. We discuss the relation of these characteristic temperatures to the calorimetric glass transition temperature Tg. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1994.090320605
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  • 2
    Electronic Resource
    Electronic Resource
    Characteristic length of the glass transition (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 2881-2892 
    Details
    ISSN: 0887-6266
    Keywords: poly(n-alkyl methacrylates) ; glass transition ; molecular cooperativity ; DSC ; heat capacity spectroscopy ; αβ splitting ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The definition of molecular cooperativity is discussed. The characteristic length of the glass transition describes the size of this cooperativity. Differential scanning calorimetry (DSC) and heat capacity spectroscopy (HCS) results of a series of poly(n-alkyl methacrylates) (alkyl = methyl, ethyl, propyl, butyl, pentyl, hexyl, and octyl) and a series of statistical copolymers poly(n-butylmethacrylate-stat-styrene) are discussed in terms of molecular cooperativity in the αβ splitting region, where a high-frequency dispersion zone a splits off into the main transition zone α and a Goldstein Johari process β at lower frequencies. The characteristic length tends to small values of order one monomer diameter in the splitting region for scenarios with an α relaxation onset. The statements about the size scale of cooperativity are conditional upon certain assumptions leading to the equation used for calculation of this size from HCS and DSC data. The step height of heat capacity (Δcp) and, with less certainty, the square root of the cooperativity volume or number (V1/2α or 1/2α) are proportional to the temperature distance from the cooperativity onset, T = Tons. © 1996 John Wiley & Sons, Inc.
    Additional Material: 13 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Modulated differential scanning calorimetry in the glass transition region. V. Activation energies and relaxation times of poly(ethylene terephthalate)s (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 2941-2952 
    Details
    ISSN: 0887-6266
    Keywords: temperature-modulated calorimetry (TMC) ; temperature-modulated differential scanning calorimetry (TMDSC) ; heat capacity ; glass transition ; heat flow calorimeter ; irreversible thermodynamics ; activation energy ; poly(ethylene terephthalate) ; hysteresis ; enthalpy relaxation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Temperature-modulated differential scanning calorimetry is used to evaluate the kinetics of the glass transition from measurement of the first harmonic of the apparent, reversing heat capacity. The data are taken from quasi-isothermal experiments with negligible instrument lag, extrapolated to zero modulation amplitude. Equations based on irreversible thermodynamics that can be understood in terms of the hole theory of liquids are applied to measurements on amorphous, semicrystalline, and biaxially drawn poly(ethylene terephthalate)s (PET). The activation energy of amorphous PET decreases from 328 to 153 kJ/mol on crystallization and to 111 kJ/mol on orientation, and is correlated with an increase in the preexponential factor. After annealing of the crystallized samples below the glass transition temperature, the activation energy of the semicrystalline PET can recover beyond the level of amorphous PET, to 387 kJ/mol. The earlier observed decrease in enthalpy relaxation on crystallization is linked to this sharp decrease in activation energy. © 1996 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Photon correlation spectroscopy of bulk poly(n-hexyl methacrylate) near the glass transition (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 2291-2305 
    Details
    ISSN: 0887-6266
    Keywords: glass transition ; polymer dynamics ; photon correlation spectroscopy ; dynamic heterogeneities ; longitudinal density fluctuations ; poly(n-hexyl methacylate) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Slowly relaxing longitudinal density fluctuations in an optically perfect sample of bulk poly(n-hexyl methacrylate) (PHMA) have been studied by photon correlation spectroscopy in the temperature range 10-36°C. The glass transition temperature for this sample was measured to be Tg = -3°C by differential scanning calorimetry. The optical purity of the sample was verified by Rayleigh-Brillouin spectroscopy and the Landau-Placzek ratio was observed to be 2.3 at 25°C. Light-scattering relaxation functions were obtained over the time range 10-6-1 s. The shape of the relaxation functions broadened as the temperature was lowered towards the glass transition. Quantitative analysis of the results was carried out using the Kohlrausch-Williams-Watts (KWW) function to obtain average relaxation times, 〈τ〉, and width parameters, β. The width parameter decreased from 0.43 to 0.21 over the temperature interval, as suggested by visual inspection. Average relaxation times shifted with temperature in a manner consistent with previous mechanical studies of the primary glass-rubber relaxation in PHMA. The relaxation functions were also analyzed in terms of a distribution of relaxation rates, G(Γ). The calculated distributions were unimodal at all temperatures. The average relaxation times obtained from G(Γ) were in agreement with the KWW analysis, and the shape of the distribution broadened as the sample was cooled. The rate at which G(Γ) displayed a maximum correlated well with the corresponding frequency of maximum dielectric loss for PHMA. The temperature dependence of these two quantities could be reproduced with an Arrhenius activation energy of 21 Kcal/mol. A consistent picture of the molecular dynamics of PHMA near the glass transition requires a strong secondary relaxation process with a different temperature dependence from the primary glass-rubber relaxation. The present results suggest that the behavior of PHMA is similar to the other poly(alkyl methacrylates). © 1996 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    High-pressure calorimetric study of plasticization of poly(methyl methacrylate) by methane, ethylene, and carbon dioxideIssued as NRCC No. 37614. (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 2635-2639 
    Details
    ISSN: 0887-6266
    Keywords: poly(methyl methacrylate) ; compressed gases ; glass transition ; plasticization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Glass transition in the system poly(methyl methacrylate)/compressed gas was studied as a function of the gas pressure p using a high-pressure Tian-Calvet heat flow calorimeter. Measurements were made on PMMA-CH4-C2H4, and ;-CO2 at pressures to 200 atm. All three gases plasticize the polymer leading to depression of the glass transition temperature Tg. Trends in the Tg depression were the same as those reported for the solubility of these gases in PMMA; the higher the solubility the larger the depression in Tg. CO2 was found to be the most effective plasticizer producing a depression of about 40°C at a pressure of about 37 atm. In the low-pressure limit, the pressure coefficient of the glass transition temperature (dTg/dp) was found to be about -0.2°C atm-1 for PMMA-CH4, the same as that observed for polystyrene-CH4. For PMMA-C2H4, the pressure coefficient was -0.7°C atm-1, which is lower than the value of -0.9°C atm-1 observed for PS-C2H4. The pressure coefficient for PMMA-CO2 was found to be about -1.2°C atm-1, which is larger than the value of -0.9°C atm-1 observed for PS-CO2. © 1996 John Wiley & Sons, Inc.
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  • 6
    Electronic Resource
    Electronic Resource
    Pressure-volume-temperature properties and free volume parameters of PEO/PMMA blends (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 1061-1080 
    Details
    ISSN: 0887-6266
    Keywords: polymer blends ; dilatometry ; free volume ; specific volume ; excess volume ; compressibility ; thermal expansivity ; equation of state ; scaling parameters ; crystallinity ; glass transition ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Melt-miscible polymer blends of poly(ethylene oxide)/atactic poly(methyl methacrylate (PEO/a-PMMA)) were prepared by melt-mixing and characterized by pressure-volume-temperature (PVT) dilatometry in the pressure and temperature range of 0 to 200 MPa and 20 to 200°C, respectively. The PVT data were analyzed in terms of two equations of state (EOS). The empirical Tait EOS was applied in the glassy, semicrystalline, and equilibrium melt state, and the Simha-Somcynsky EOS theory was applied in the equilibrium melt and glassy state. The Simha-Somcynsky EOS theory contains a free volume function. The temperature, pressure, and composition dependence of the free volume fraction h calculated from the Simha-Somcynsky EOS theory was studied. As a function of blend composition we observe that the free volume fraction, thermal expansivity, and compressibility all deviate mainly positively from linearity while the specific volume deviates mainly negatively from linearity. These findings are reconciled with composition-dependent free volume parameters, the free volume and cell volume as well as with self- and cross-interaction parameters derived from the Simha-Somcynsky EOS theory as applied to polymer mixtures. Moreover, the pressure dependence of glass and melting transitions as well as crystallization kinetics have been investigated. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1061-1080, 1998
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  • 7
    Electronic Resource
    Electronic Resource
    Description of thermal relaxation of polystyrene close to the thermal glass transition (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2165-2175 
    Details
    ISSN: 0887-6266
    Keywords: temperature-modulated differential scanning calorimetry ; DSC ; heat capacity ; glass transition ; thermal relaxation ; polystyrene ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The glass transition can be measured at different experimental conditions. Using spectroscopic methods at relative high frequency the α-relaxation is measured in the thermodynamic equilibrium. In the caloric case we call this phenomenon thermal relaxation transition (TRT). With a conventional differential scanning calorimeter (DSC) the transition of the equilibrium (the melt) into a nonequilibrium (the glassy state) is measured. This effect is called thermal glass transition (TGT). In contrast to the TGT, the TRT can be described using the linear response approach. The temperature-modulated differential scanning calorimetry (TMDSC) technique superimposes a periodical temperature perturbation upon the constant scanning rate of conventional DSC. This technique combines a spectroscopic method with a linear temperature scan. Both the TGT and the TRT are measured simultaneous. Because the frequencies are relatively low in a TMDSC experiment, the temperature ranges of both transitions overlap. In this case, the experimental results show an influence of the TGT on the TRT. The reason of that is the deviation from the nonequilibrium. In this case, the fictive temperature is different from the external temperature. This effect can be described by means of a Tool-Narayanaswamy-Moynihan model for the TGT. Based on this model, a description of the complex heat capacity close to the thermal glass transition is shown. The influence of the beginning freezing-in process on the thermal relaxation is characterized by the fictive temperature. Using the presented description, a quantitative calculation of the nonlinear effects in the thermal relaxation is possible. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2165-2175, 1998
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  • 8
    Electronic Resource
    Electronic Resource
    Glass transition, crystallization, and morphology relationships in miscible poly(aryl ether ketones) and poly(ether imide) blends (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 901-915 
    Details
    ISSN: 0887-6266
    Keywords: poly(aryl ether ketones) ; poly(ether imide) ; crystallization ; melting ; glass transition ; morphology ; small-angle x-ray scattering ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The relationships among glass transition, crystallization, melting, and crystal morphology of poly(aryl ether ketone) (PAEK)/poly(other imide) (PEI) blends was studied by thermal, optical and small-angle x-ray scattering (SAXS) methods. Two types of PAEK were chosen for this work: poly(aryl ether ether ketone), PEEK, and poly(aryl ether ketone ketone), PEKK, which have distinctly different crystallization rates. Both PAEKs show complete miscibility with PEI in the amorphous phase. As PAEK crystallizes, the noncrystallizable PEI component is rejected from the crystalline region, resulting in a broad amorphous population, which was indicated by the broadening and the increase of Tg over that of the purely amorphous mixture. The presence of the PEI component significantly decreases the bulk crystallization and crystal growth rate of PAEK, but the equilibrium melting temperature and crystal surface free energies are not affected. The morphology of the PEI segregation was investigated by SAXS measurements. The results indicated that the inter(lamellar-bundle) PEI trapping morphology was dominant in the PEEK/PEI blends under rapid crystallization conditions, whereas the interspherulitic morphology was dominant in the slow crystallizing PEKK/PEI blends. These morphologies were qualitatively explained by the expression δ=D/G, where G was the crystal growth rate and D was the mutual diffusion coefficient. © 1993 John Wiley & Sons, Inc.
    Additional Material: 21 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1993.090310801
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  • 9
    Electronic Resource
    Electronic Resource
    On the plasticization of poly(2,6-dimethyl phenylene oxide)Issued as NRCC No. 37569. by CO2 (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 2549-2553 
    Details
    ISSN: 0887-6266
    Keywords: plasticization ; poly(2,6-dimethyl phenylene oxide) ; PPO-CO2 ; glass transition ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Change in the glass transition temperature, Tg, of poly(2,6-dimethyl phenylene oxide), PPO, due to the dissolved CO2 has been measured as a function of the gas pressure, p, using a high-pressure DSC cell. At 61.2 atm, the highest pressure studied, Tg is depressed by 31.6°C. The depression in Tg is found to be linear with pressure, with dTg/dp of -0.5°C atm-1. The experimental results are in fair agreement with those calculated from a quasilattice solid-solution model for polymer-diluent systems. The present results, however, differ markedly from a recent investigation on PPO-CO2 system which reported a depression in Tg of 226°C at 60 atm and a dTg/dp of -3.8°C atm-. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1994.090321512
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  • 10
    Electronic Resource
    Electronic Resource
    About the microstructure of PCVD prepared crystal mats of statistical oligo-vinylidene-fluoride-trifluoroethylene in relation to other fluorinated polymers (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 237-246 
    Details
    ISSN: 0887-6266
    Keywords: oriented fluoro-oligomers ; chemical vapor deposition ; ferroelectricity ; glass transition ; Brillouin spectroscopy ; x-ray diffraction ; vinylidene fluoride ; trifluoroethylene ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The room temperature phase of the physical/chemical vapor-deposited statistical co-oligomer VDF/TrFE(70/30) has been characterized by different experimental methods such as small-angle x-ray scattering, wide-angle x-ray diffraction, size-exclusion chromatography, infrared absorption and optical refractometry. The characterization of the elastic properties was carried out using high-performance Brillouin spectroscopy in connection with special scattering geometries. The co-oligomer VDF/TrFE(70/30) was obtained by cracking the parent statistical copolymer and subsequently vapor depositing the shortened chains on highly oriented PTFE substrates (PIA-technique). The room temperature phase of the resulting oriented waxy crystal mats of VDF/TrFE(70/30) is predominantly ferroelectric. The physical properties are very different to those of similarly PIA-prepared n-alkanes, perfluoroalkanes, and blockfluoroalkanes. The microstructure of VDF/TrFE(70/30) is interpreted in terms of partially crystalline nano-sized structures giving rise to a marked freezing process below room temperature. © 1995 John wiley & Sons, Inc.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1995.090330208
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