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  • 1
    Electronic Resource
    Electronic Resource
    Scale of cooperative γ-relaxation of bisphenol A polycarbonate (1992)
    s.l. : American Chemical Society
    Macromolecules 25 (1992), S. 6800-6809 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00051a012
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  • 2
    Electronic Resource
    Electronic Resource
    Correlation between the Shear Yielding Behavior and Secondary Relaxations of Bisphenol A Polycarbonate and Related Copolymers (1994)
    s.l. : American Chemical Society
    Macromolecules 27 (1994), S. 2761-2768 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00088a017
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  • 3
    Electronic Resource
    Electronic Resource
    Syntheses of alternating multiblock copolycarbonates with controlled block lengths (1991)
    s.l. : American Chemical Society
    Macromolecules 24 (1991), S. 1590-1594 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00007a022
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  • 4
    Electronic Resource
    Electronic Resource
    Secondary relaxation motion in bisphenol A polycarbonate (1991)
    s.l. : American Chemical Society
    Macromolecules 24 (1991), S. 1905-1913 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00008a031
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  • 5
    Electronic Resource
    Electronic Resource
    Fracture toughness and fracture mechanisms of polybutylene-terephthalate/polycarbonate/ impact-modifier blends (1994)
    Springer
    Journal of materials science 29 (1994), S. 4510-4522 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A series of polybutylene-terephthalate/polycarbonate (PBT/PC) blends with different compositions were prepared using a twin-screw extruder. The morphologies of the blends were revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that a 50/50 PBT/PC blend possessed a bicontinuous structure and the other blends had a dispersed phase of either PBT or PC depending on which was the minor component. A relatively strong interface was observed in the blends with 20%, 40% and 50% PBT; but poor interfacial adhesion was found in the blends with 60% and 80% PBT. The strength of the interfacial boundary was believed to depend on the composition and blending conditions of the individual blend. Fracture experiments showed that the sharp-notch fracture toughness of PC could be significantly increased by mixing with up to 50% PBT without losing its modulus and yield stress. The toughening mechanisms involved in the fracture processes of the blends were studied using both SEM and TEM together with single-edge-double-notched-bend (SEDNB) specimens. It was found that in the toughened blends the growing crazes initiated by the triaxial stress in front of the crack tip were stabilized by the PC domains. The debonding-cavitation mechanism occurred at the PBT/PC interface, which relieved the plane-strain constraint and promoted shear deformation in both PBT and PC. This plastic deformation absorbed a tremendous amount of energy. Crack-interface bridging by the PC domains was clearly verified by the TEM study. Thus, the PC domains not only stabilized the growing crazes they also bridged crack surfaces after the crack has passed by. This effect definitely caused a large plastic-damage zone and hence a high crack resistance. Poor crack resistances of the blends rich in PBT was caused by the poor interfacial adhesion between PBT and PC. In these polymer blends, the growing crazes easily developed into cracks, which subsequently passed through the weak interface of PBT/PC and finally produced fast unstable fracture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00376274
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  • 6
    Electronic Resource
    Electronic Resource
    Prediction of Physical Aging in Controlled-Release Coatings: The Application of the Relaxation Coupling Model to Glassy Cellulose Acetate (1991)
    Springer
    Pharmaceutical research 8 (1991), S. 698-705 
    Details
    ISSN: 1573-904X
    Keywords: physical aging ; water transport ; controlled-release coating ; mechanical relaxation ; cellulose acetate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of physical aging on both the water transport properties and the mechanical properties of glassy cellulose acetate was investigated. Results indicate a reduction in the mechanical rate of relaxation as well as a reduction in the water permeability as the glass ages. A model which describes the low-frequency relaxation behavior of condensed, amorphous systems is used to quantitate the mechanical relaxation data. Systematic changes in key parameters from this model signify alterations in the microscopic or short-range structure as the glass physically ages. Predictions from this model correlate quite closely with the observed water permeability reductions and thus indicate that the transport properties of glassy polymers are dependent on the structure of the glass. This approach may provide further insight into the effects of nonequilibrium behavior on pharmaceutically important properties and may serve as a basis for predicting aging and permeability changes in controlled-release dosage forms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015837614475
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  • 7
    Electronic Resource
    Electronic Resource
    The Effect of Physical Aging on the Dissolution Rate of Anionic Polyelectrolytes (1990)
    Springer
    Pharmaceutical research 7 (1990), S. 648-653 
    Details
    ISSN: 1573-904X
    Keywords: physical aging ; dissolution ; enteric coating ; creep compliance ; hydroxypropyl methylcellulose phthalate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of physical aging on the dissolution and mechanical properties of hydroxypropyl methyl-cellulose phthalate (HPMCP) was investigated. Dissolution rate measurements were performed on films which, initially above the glass transition temperature, T g, were quenched to a sub-T g storage temperature, aged at that temperature for a period of time and then quenched again to 25°C. Within the time scale of observation, reductions in the dissolution rate to a limiting value were observed. HPMCP was also found to age in the same storage temperature range as determined by a creep compliance technique. These mechanical results indicate a change in glass structure and show that a limiting density was approached. Parallel changes were observed in the dissolution rate studies suggest that dissolution rate is governed in part by glass density. Therefore, mechanical changes of glassy films can yield pharmaceutically relevant information about the extent of physical aging and serve as an indicator of the effect of aging on dissolution rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015882631082
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of cyclic stress on enthalpy relaxation in polycarbonate (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 30 (1992), S. 221-230 
    Details
    ISSN: 0887-6266
    Keywords: polycarbonate, cyclic stress and aging of ; differential scanning calorimetry (DSC) of polycarbonate under cyclic stress ; craze initiation and fatigue in glassy polymers ; glassy initiation and fatigue in glassy polymers ; glassy polymers, stress and enthalpy relaxation in ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Possible effects of cyclic stress on physical aging in polycarbonate were investigated using differential scanning calorimetry (DSC) measurements. When the enthalpy overshoot by DSC of specimens of different previous thermophysical aging histories is measured as a function of the cyclic stress amplitudes, two characteristic regimes are observed. By correlating with optical microscopic observations, these regimes are identified as the incubation and crazing stages (denoted regimes I and II, respectively). The enthalpy relaxation behavior in Regime I is similar to thermophysical aging, indicating that the glassy structure as a whole is initially shifted to one where molecular mobility is retarded by relatively low amplitude cyclic stress. A strong interaction is also seen between the enthalpy overshoot and previous physical aging. That is, the more the material is previously aged, and the shorter the incubation period, the longer the crazing region is. As a result, brittle failure occurs over a wider load range compared with less aged specimens.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1992.090300301
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of cyclic stress on structural changes in polycarbonate as probed by positron annihilation lifetime spectroscopy (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 30 (1992), S. 231-238 
    Details
    ISSN: 0887-6266
    Keywords: polycarbonate, stress-induced structural changes in ; positron annihilation spectroscopy of glassy polycarbonate after cyclic stress ; glassy polymer, structural changes in stress and aging positron annihilation study of ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Positron annihilation lifetime spectroscopy (PALS) is used to probe structural changes in glassy polycarbonate in terms of changes in the hole volume and the number density of holes during fatigue (cyclic stress) aging. The ortho-positronium (o-Ps) pickoff annihilation lifetime τ3, as well as the intensity I3, were measured as a function of cyclic stresses and various previous thermophysical aging histories. It is found that τ3, the longest of the three lifetime components resolved in the PALS of glassy polycarbonate, increases when a cyclic stress is applied. These results indicate that there is a structural change during fatigue aging. The “holes” where o-Ps can localize become larger upon fatigue aging. These results also suggest that a significant distinction exists between structural changes induced by thermophysical aging and fatigue aging. The o-Ps annihilation intensity, which is a relative measure of the hole density in a material, showed a continuous decrease upon fatigue aging, indicating the possibility of hole coalescence, which could be a precursor of crazing. The interaction between thermophysical aging and fatigue aging corresponds very well with the enthalpy relaxation behavior as reported previously, viz., a well-aged sample is much more sensitive to cyclic stress. More importantly, it is hypothesized that fatigue failure initiation is probably closely related to hole size and density fluctuation.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1992.090300302
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  • 10
    Electronic Resource
    Electronic Resource
    The preparation and morphology of PPO-epoxy blends (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 48 (1993), S. 1051-1060 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Poly(phenylene oxide) (PPO) was found to be miscible in diglycidyl ether of bisphenol A (DGEBA) based epoxy. The PPO-DGEBA system exhibited upper critical solution temperature (UCST) behavior. The cloud point temperatures were measured and found to be sensitive to the mol wt of the epoxy resin. A series of PPO-modified epoxies were cured with piperidine at 160°C, which is above the cloud point temperature. Upon cure, two phase solids were formed, which contained discrete PPO particles. However, the two-phase particulate morphology was not uniform and numerous large, occluded PPO particles were observed. In order to improve the uniformity, several styrene-maleic anhydride copolymers were evaluated as potential surfactants for PPO-DGEBA bends. The formation of a uniform, particulate morphology was facilitated by the addition of a styrene-maleic anhydride copolymer, containing a 10:1 ratio of styrene to maleic anhydride. To our knowledge, this is the first time that an emulsifying agent has been added to improve the morphology of thermoplastic modified epoxies. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1993.070480612
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