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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Macromolecules 24 (1991), S. 1117-1122 
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 3785-3791 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of polystyrene microgel (PSMG), i.e., a probe particle of highly cross-linked polystyrene latex spheres with radii 20.7 and 284 nm, during the sol–gel transition of poly(γ-benzyl-L-glutamate) (PBLG) dissolved in N,N-dimethylformamide (DMF) solution has been investigated by measurements with the dynamic light scattering technique. All the intensity time correlation functions (ICF) measured from PSMG dispersed in PBLG matrix approximately decayed single exponentially. First, it was confirmed that the diffusion coefficients of PSMG at the sol state of 298.8 K obeyed the stretched exponential relation as a function of concentration of PBLG–DMF solutions. Second, the initial amplitude and the normalized variance of ICF, and the diffusion coefficient of PSMG were altered considerably before and after sol–gel transition with decreasing temperature. The initial amplitude and the normalized variance had a minimum and a maximum at the gelation threshold temperature, respectively. It was also found that PSMG almost free-diffused even at the gel state, as well as the sol state, regardless of low temperature. These facts may strongly support that the resulting PBLG gels induced through microphase separation evidently had a porous and bicontinuous structure at the "swollen gel state," which corresponds to the results observed by a transmission electron microscope. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 27 (1989), S. 795-807 
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An allophanate-cured polyurethane (PU) has been prepared. The relationship between trifunctional network structure and mechanical properties is discussed. Mooney-Rivlin constants C1 and C2 are determined from stress-strain isotherms. C2 is approximately constant. The average value of structure factor A3 in the limit at large deformation is 0.432, in fair agreement with the theoretical prediction of 1/3. The structure factor A′3 of all PU samples becomes roughly unity in the limit at small deformation. The experimental results are interpreted by the recent Flory theory (a fluctuation-constraint model of junctions). The κ parameter decreases with increasing crosslink density; the ξ parameter is small and approaches zero. Increasing crosslink density tends to cause phantom deformation for extended PU networks. However, the absolute value of the reduced stress in the limit at large deformation (or for the equivalent phantom network) [fph*] is believed to be overestimated for PU networks with high crosslink density. The origin of this behavior is discussed in detail.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 27 (1989), S. 809-817 
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Chemical stress relaxation (CSR) of allophanate-cured polyurethane (PU) was measured under two kinds of degradation conditions: (1) degradation in butylamine (BuNH2)/dimethyl sulfoxide solution; (2) degradation at high temperature in nitrogen. The allophanate groups of the crosslink sites in PU networks are selectively cleaved by BuNH2, and CSR is not influenced by the crosslink density within experimental error. This suggests the validity of Tobolosky's method for distinguishing between random scission along network chains and the cleavage of crosslinks from the dependence of CSR on crosslink densities. In addition, CSR of PU samples degraded at high temperature in nitrogen was also found to be independent of the crosslink density. It follows that thermal degradation of PU networks occurs by the cleavage of crosslink sites in the same manner. CSR is compared with the relative degree of thermal degradation of PU sample, determined by-the amine-decomposition method and the swelling method. Consequently, the total (or residual) crosslink density of degraded PU networks corresponds essentially to the intermittent CSR.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0935-9648
    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: We have presented a simple technique for the fabrication of nanocrystals of organic molecules and polymers and have shown that it is possible, using the liquid-phase technique, to fabricate organic nanocrystals ranging in size from 10 nm to 1 μm by manipulating the preparative conditions. In particular, nanocrystals of poly(4-BCMU) ranging from 20 nm to 350 nm were prepared by controlling the preparation conditions. The main advantages of the liquid-phase technique are the practicality and suitability of the technique for a wide range of materials. The fabrication of organic nanocrystals, though at a very early stage, seems a promising approach for producing low-dimensional organic materials and, like inorganic nanocrystals, another important objective for future study would be to incorporate organic nanocrystals into a variety of inorganic and organic media. It is hoped that extensive work will be done on organic nanocrystals to evaluate their potential for electronics and photonics.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 34 (1987), S. 223-233 
    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: Networks were prepared in the swollen and dry states to investigate the influence of physical relaxation on chemical stress-relaxation. The stress-relaxation behavior of solution-cured samples was different significantly from that of the samples crosslinked conventionally. The same result was also observed in the number of chain scission for both kinds of samples. On the other hand, the number of chain scission estimated by using the swelling method for samples crosslinked conventionally was in good agreement with that by the chemical stress-relaxation for solution-cured samples. It was found that there is little or no influence of the physical relaxation caused by entanglements, and no effect of dangling chains arising from scission in the equilibrium swelling. The relative change of network chain density determined by means of the swelling method was also consistent with that by sol fraction determination. These results indicate that the swelling method can be used as a measure of a degree of degradation on chemorheology. Taking into account the influence of physical relaxation on chemical stress-relaxation, a new relationship between the relative stress decay and the relative network chain density was experimentally proposed.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1042-7147
    Keywords: poly(4-BCMU) ; polydiacetylene ; nanocrystals ; microcrystals ; 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
    Notes: A novel wet water-ethanol-borne technique of preparing nanocrystals of the poly[5,7-dodecadiyn-1,12-diol bis-(n-butoxycarbonylmethyl urethane)], oxoreferred to as poly(4-BCMU), is reported for the first time. The fabrication of poly(4-BCMU) nanocrystals with sizes ranging from a few to hundreds of namometers is presented. The spectroscopic analysis of the poly(4-BCMU) nanocrystals using nuclear magnetic resonance, infrared, optical absorption spectroscopy, gel permeation chromatography and scanning electron microscopic techniques is discussed. A structural characterization at molecular level of the poly(4-BCMU) constituting the nanocrystals evidences the maintenance of the molecular integrity of the polydiacetylene backbone.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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