Mechanische Relaxationserscheinungen in vernetztem und gequollenem Polystyrol

Illers, K. H.; Jenckel, Ernst

doi:10.1007/bf01968891

Cited by 69 publications

(19 citation statements)

References 6 publications

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“…At lower temperatures, in disagreement with some authors, the analyzed PS homopolymer does not exhibit any relaxation, in particular, near 160 K. According to these authors, the PS homopolymer exhibits a relaxation related to the phenyl rotations 5~16 or to termination by coupling of two growing PS chains. 15 This result adds to the controversy about the existence/origin of such a relaxation.…”

Section: Dynamic Mechanical Spectrometrymentioning

confidence: 88%

Molecular mobility in styrene‐co‐methacrylic acid random copolymers from 100 to 450 K

Albérola

Bergeret

Battesti

et al. 1993

J of Applied Polymer Sci

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SYNOPSISMolecular mobility of both the polystyrene homopolymer and a series of styrene-co-methacrylic acid copolymers with various amounts of methacrylic acid is analyzed in the temperature range from 100 to 450 K, by high-resolution dynamic mechanical spectrometry, IR, and differential scanning calorimetry. Isochronal spectrometry exhibits for polystyrene homopolymer two relaxations, the @ and a relaxations, with increasing temperature. Styreneco-methacrylic acid copolymers exhibit three mechanical relaxations, the ?, @, and a relaxations, from 100 to 450 K. These relaxations could be related to the progressive occurring of motions of the side groups and of the backbone chains when increasing the temperature. This could be due to the progressive breakdown of hydrogen bonds, which could show a somewhat wide range of magnitude. Furthermore, the decreasing of the magnitude of the a relaxation with increasing methacrylic acid content could suggest the presence of a stable network of chemical cross-links induced by the presence of anhydride so that molecular mobility could be partially inhibited above TE. The remaining of a fluctuation network of hydrogen bonds (labile contacts) above TE could also emphasize the decrease in molecular mobility. 0 1993 John Wiley & Sons, Inc.

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Section: Dynamic Mechanical Spectrometrymentioning

confidence: 88%

Molecular mobility in styrene‐co‐methacrylic acid random copolymers from 100 to 450 K

Albérola

Bergeret

Battesti

et al. 1993

J of Applied Polymer Sci

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“…However, its very existence and its molecular interpretation are still in question. It has been shown [18,19] that location and height of the ? maximum are strongly influenced by plasticizers.…”

Section: Specific Volume Versus Temperature Curves At Constant Rate Omentioning

confidence: 99%

“…Using eqs. (13)(14)(15) and (18), the retardation time in the differential equation (12) time for polystyrene at various temperatures in the transition region [45] where rs is the retardation time in a state of thermodynamic equilibrium at the temperature T~. rs is the only-temperature independent-parameter which occurs in the nonlinear differential equation.…”

Section: V(o)-v(t)=fi'[log(t/t6+ 1)-log(t/tm+mentioning

confidence: 99%

Thermal contraction and volume relaxation of amorphous polymers

1984

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Abstract." Two experimental techniques are described for the determination of the change of specific volume of polymers with temperature and aging time, which allow measurements between -160 °C and + 200 °C. Four technical amorphous polymers, PS, PVC, PMMA and PC have been investigated. Volume-temperature curves under constant rate of cooling are presented and interpreted with respect to relaxation processes known from other physical investigations. The rate dependence of dilatometric glass transition temperatures is compared with the time dependence of rheometric glass transition temperatures from shear creep data. Volume relaxation data at constant aging temperature are presented. Aging is found to proceed until very low temperatures in the glassy state for e.g. PMMA.For polystyrene, a comparison is made between the predictions of a very simple theory of volume relaxation due to Kovacs with experimental data, using additional information from volume temperature curves and the time temperature shift of the shear creep transition. The theory predicts a rate of volume relaxation which is much lower than that found by experiment.

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“…This indicates that the dissipation of energy, over a wide range of frequencies is higher for the hydrogel which contains some level of frozen water than for the gel containing liquid water. The large loss tangent (with an upward curvature) at T Ͻ T mw , suggests the existence of a secondary (b) mechanical relaxation, such as that observed in swollen polystyrene [17] and in semicrystalline polymers [18]. However, the loss tangent peak for such a relaxation must occur at a temperature lower than our experimental limitation of T Ϫ 22ЊC.…”

Section: Resultsmentioning

confidence: 76%

Rheology of highly swollen chitosan/polyacrylate hydrogels

Jiang

Mather

et al. 1999

Polymer

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Recently we reported on chitosan hydrogel systems having excellent laser damage resistance. The measured laser damage threshold (LDT) was better than BK7 glass and quartz, commonly used inorganic optical materials, and 20 to 35 times higher than commercial PMMA, a popular polymer optical material. In this study, we continue our investigation of the phase transition behavior of water within the hydrogels by means of oscillatory shear rheology. The crystallization and melting behavior of ice in these hydrogels is greatly affected by the internal structure of the network. Changes in this structure are probed by comparing differences in the rheological measurements at temperatures above and below freezing. Trends among the measured shear storage modulus (G H ), shear loss modulus (G HH ) and shear loss tangent (tan d) are shown to be related to the mobility of water within the gels. The activation energy associated with the melting of ice in a particular hydrogel was found to be significantly higher than the melting enthalpy of pure ice, suggesting imperfection in the ice crystals and/or a low degree of crystallinity in the hydrogel. ᭧

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Mechanische Relaxationserscheinungen in vernetztem und gequollenem Polystyrol

Cited by 69 publications

References 6 publications

Molecular mobility in styrene‐co‐methacrylic acid random copolymers from 100 to 450 K

Molecular mobility in styrene‐co‐methacrylic acid random copolymers from 100 to 450 K

Thermal contraction and volume relaxation of amorphous polymers

Rheology of highly swollen chitosan/polyacrylate hydrogels

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