Research Outputs

Permanent URI for this communityhttps://hdl.handle.net/20.500.14288/2

Browse

Filters

2003 - 20073

Advanced Search

Filter by

Settings

Quartile: search.filters.quartile.Q4Subject: search.filters.subject.Polymers

Search Results

Now showing 1 - 3 of 3
  • Placeholder
    PublicationMetadata only
    Effect of symmetry and h-bond strength of hard segments on the structure-property relationships of segmented, nonchain extended polyurethanes and polyureas
    (Taylor and Francis Inc, 2007) Das, Sudipto; Cox, David F.; Wilkes, Garth L.; Klinedinst, Derek B.; Beyer, Frederick L.; Department of Chemistry; Department of Chemistry; Yılgör, İskender; Yılgör, Emel; Faculty Member; Researcher; Department of Chemistry; College of Sciences; College of Sciences; 24181; 40527
    Segmented, nonchain extended polyurethanes and polyureas based on PTMO soft segments (SS) anti hard segments (HSs) based on only single molecules of a diisocyanate were synthesized. Type and nature of the diisocyanate was systematically varied in order to analyze the effect of HS symmetry and type of linkage between the HS and SS on the structure-property relationship of these segmented copolymers. Results showed that the increased symmetry of the diisocyanates allows a more efficient packing of the HSs which leads to a microphase-separated structure with the crystalline hard ribbon or thread-like domains percolated throughout the SS matrix, even with a low HS content (ca. 13 wt.%). The service window of these segmented copolymers was significantly influenced by the symmetry and type of linkage between the HS and SS. Most copolymers also showed evidence of strain hardening accented by the strain induced crystallization of the PTMO SS.
  • Placeholder
    PublicationMetadata only
    Exploring urea phase connectivity in molded flexible polyurethane foam formulations using LiBr as a probe
    (Marcel Dekker Inc, 2003) Aneja, A; Wilkes, GL; Department of Chemistry; Department of Chemistry; Department of Chemistry; Yılgör, İskender; Yılgör, Emel; Yurtsever, İsmail Ersin; Faculty Member; Researcher; Faculty Member; Department of Chemistry; College of Sciences; College of Sciences; College of Sciences; 24181; N/A; 7129
    Lithium bromide (LiBr) was incorporated in formulations based on molded flexible polyurethane foams in order to alter systematically the phase separation behavior and thus give insight into urea phase connectivity. The formulations of the materials generated were similar to those of molded flexible polyurethane foams except that a surfactant and a low, molecular weight cross-linking agent (such as diethanol amine) were not used. The resulting materials were evaluated by using the techniques of atomic force microscopy (AFM), SAXS, and DSC. Atomic force microscopy and SAXS were used to demonstrate that the materials with and without LiBr were microphase separated and possessed average interdomain spacings of ca. 90 Angstrom, typical of flexible polyurethane foams. AFM phase images also showed that incorporation of LiBr reduced the urea phase aggregation, which is known to take place in flexible polyurethane foams, and led to a more homogeneous, distribution of the urea microdomains in the soft polyol phase. Addition of LiBr also decreased the regularity in segmental packing of the hard segments, as was noted by using WAXS. DSC scans revealed that inspite of the significantly different morphologies noted for the samples with different LiBr contents, soft-segment mobility, as reflected by its T-g, remained unaffected on including this additive at the concentrations investigated. Interaction of LiBr with diethyl ether (DEE), 1,3-dimethylurea (DMU) and a model urethane (1,3-dimethylcarbamate) (URET) also was estimated by quantum mechanical calculations (QMC) by using density functional theory (DFT). For DMU and URET, QMC indicated a strong interaction of the Li+ ion with ether and carbonyl oxygens, and of the Br- with the (N-H) protons. Interaction energies of Li+ with DEE (O...Li+), URET (C=O...Li+), and DMU (C = O.....Li+) complexes were calculated to be -201, -239 and -272 kJ/mole, respectively. Interaction energies of DEE, URET, and DMU complexes with LiBr were calculated to be -198, -620, and -691 kJ/mole, respectively, suggesting that the interaction of the salt was predominantly with the hard segments (urea and urethane) and not with the polyether soft segments.
  • Placeholder
    PublicationMetadata only
    Structure - property behavior of new segmented polyurethanes and polyureas without use of chain extenders
    (Amer Chemical Soc Inc, 2005) Klinedinst, DB; Beyer, FL; Sheth, JP; Wilkes, GL; N/A; Yılgör, Emel; Yılgör, İskender; Researcher; Faculty Member; N/A; N/A; 24181
    New novel segmented polyurethane and polyurea copolymers have been synthesized without chain extenders and the structure-property behavior of these systems has been investigated. It is shown that by the proper choice of diisocyanate and its symmetry, one can obtain highly microphase separated systems without chain extenders and that the materials also display useful mechanical behavior. In particular, it is shown that due to the bidentate hydrogen bonding achieved in the segmented ureas, a significant modulus "service temperature window" is also obtained. It is also verified that not only can strong microphase separation be obtained with low weight fraction hard segment content (14%) but that the hard phase, which is comprised of monodisperse "single molecule" units, also displays a percolated thread-like structure throughout the dominant soft segment material - the latter being based on ca. 1000 g/mol polytetramethylene oxide.