Influence of chain extenders and chain end groups on properties of segmented polyurethanes. I. Phase morphology

Savelyev, Yu.V.; Akhranovich, E.R.; Grekov, A. P.; Привалко, Е. Г.; Korskanov, V. V.; Shtompel, V. І.; Privalko, V. P.; Pissis, P.; Kanapitsas, A.

doi:10.1016/s0032-3861(97)10101-x

Cited by 57 publications

(21 citation statements)

References 9 publications

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“…This technique can be applied to polar materials and seems to be ideal for studies of PU materials. Several dielectric relaxation studies of the linear and branched PU systems have been reported in the literature [12][13][14], in particular on the molecular dynamics 0022 under pressure dependence [15] or the effect of the interfacial interactions [16]. Roussos et al investigated novel linear/low-branched polyurethanes by means of dielectric techniques [17].…”

Section: Introductionmentioning

confidence: 99%

Polyurethane networks based on hyperbranched polyesters: Synthesis and molecular relaxations

Czech

Okrasa

Boiteux

et al. 2005

Journal of Non-Crystalline Solids

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Several polyurethane networks based on hyperbranched polyesters (trade name Boltorn Ò H40) were synthesized. Molecular dynamics in these systems were investigated by means of broadband dielectric spectroscopy and comparatively by dynamic mechanical analysis. Glass transition temperatures were determined by differential scanning calorimetry. It was found that these techniques yield consistent results concerning molecular relaxation processes, however, the dielectric spectroscopy appears to be the most sensitive to show the secondary relaxation processes. The molecular relaxations are much more sensitive to the changes of the chemical character of polyurethane linear links between the hyperbranched centers, than to crosslinking density changed by the length of linear PU chains. The weak influence of the PU chain length on the molecular properties can be explained by the existence of hydrogen bonds forming a physical network, which is more dense and consequently, much stronger than the chemical network in the investigated temperature range.

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Section: Introductionmentioning

confidence: 99%

Polyurethane networks based on hyperbranched polyesters: Synthesis and molecular relaxations

Czech

Okrasa

Boiteux

et al. 2005

Journal of Non-Crystalline Solids

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“…Polyurethanes (PUs) are characterized by a two-phase microstructure, consisting of hard-segment (HS) microdomains dispersed in a soft-segment (SS) phase [1][2][3]. It is this microstructure that is responsible for most of the extraordinary properties of PUs utilized in many applications.…”

Section: Introductionmentioning

confidence: 99%

“…However, the microphase separation (MS), arising from the thermodynamical incompatibility of HS and SS, is not complete, even at complete incompatibility of the segments, due to covalent bonds between them [4]. Several factors affect the degree of microphase separation (DMS), such as the polarity and length of the segments, the crystallinity of each segment, and the overall composition and flexibility of the high-segment microdomains [3]. According to Koberstein and co-workers [5], a critical HS length is required for microphase separation, whereas DMS generally improves with an increase in the HS content.…”

Section: Introductionmentioning

confidence: 99%

“…PUs are often prepared by a two-step process: formation of prepolymer (PP) with reactive NCO groups by the reaction of a low-molecular-weight polyether or polyester with an aromatic or aliphatic diisocyanate (DIC) at the first stage, which is extended with a low-molecular-weight diol or diamine (chain extender, CE) at the second stage [2,3,8,13]. The ratio PP:CE is very often chosen close to the stoichiometric 1:1, as it has been anticipated that no linear PUs are formed when the mole fraction of CE is significantly reduced [33].…”

Section: Introductionmentioning

confidence: 99%

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Comparative dielectric studies of segmental mobility in novel polyurethanes

et al. 2004

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Molecular dynamics in selected novel linear/low-branched polyurethanes (PUs), based on oligo(oxytetramethylene glycol), 4,4'-diphenylmethanediisocyanate (MDI) or 2,6-toluenediisocyanate (TDI), and unsymmetrical dimethylhydrazine (I) and a derivative of that (II) as chain extenders (CE), were studied by dielectric techniques. Special attention was paid to the investigation of the α relaxation, associated to the glass transition, by dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarization currents (TSDC). The TSDC method was used to study the interfacial Maxwell-Wagner-Sillars (MWS) relaxation, related to the accumulation of charges at the interfaces between soft-segment and hardsegment microdomains. The results obtained by DRS and TSDC were in good agreement with each other and in reasonable agreement with results for the microphase separation (MS) obtained by small-angle X-ray scattering and differential scanning calorimetry. TSDC proved to be an attractive complementary technique to DRS for the study of MS in PUs. The results suggest that the position of the MWS band, as well as its separation from the α band, is a good measure of the degree of MS. As regards the PUs studied here, the degree of MS enhances by increasing the mole ratio of CE, and by replacing MDI by TDI or CE I by CE II.

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“…Thermal characteristics 33,34 of the PUs are often expressed by the T g and measured with thermal analyzers. For example, the difference of the TDIbased to the related segmented PUs of the methylene diphenyl diisocyanate (MDI)-butanediol system [35][36][37] can be made with the measurement at their T g by a thermal analyzer such as DSC. The DSC spectrum of the MDI-based PU shows the endothermic peak after the T g indicating the separated hard and soft domains in the morphology, whereas, the 2,4-TDI-based PU shows only the T g , indicating the well-mixing of the soft and hard segment.…”

Section: Introductionmentioning

confidence: 99%

Characterization of the relaxation transitions in toluene diisocyanate-based polyurethanes with poly(propylene glycol) as the soft segment by thermally stimulated current depolarization with relaxation mapping analysis

Hsu

Yang

Huang

1999

J. Appl. Polym. Sci.

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Thermal relaxation transitions of toluene diisocyanate (TDI)-based polyurethanes (PU) were characterized by the thermally stimulated current (TSC) technique with verification data from the relaxation mapping analysis (RMA) measurement. TDI-based PU elastomers with poly(propylene glycols) (PPG) as the soft segment and methylene-bis-orthochloroaniline (MOCA) as the hardener, showed three relaxation transitions, (1) a subglass transition (T g ) of the terminal groups occurred near Ϫ135°C; (2) the T g ; and (3) a global transition occurred above the T g (assigned as T global transition). The temperature of T g of PU as expected was varied by the chain length and attributed by the motion of an urethanic chain dominated by the soft segment and may also associate in the cooperative movement with the hard segment. The T global transition appearing above the T g was identified and attributed to the global transition in the macromolecule scale and was supported by the tangent plot of the dynamic mechanical analyzer (DMA) measurement. The TSC measurement on thermal characteristic transitions of TDI-based PU provided a whole range of thermal transitions including a sub-T g , the T g (observed by DSC) to a global transition (may be observed by DMA) with the ease of sample preparation in one single measurement.

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Influence of chain extenders and chain end groups on properties of segmented polyurethanes. I. Phase morphology

Cited by 57 publications

References 9 publications

Polyurethane networks based on hyperbranched polyesters: Synthesis and molecular relaxations

Polyurethane networks based on hyperbranched polyesters: Synthesis and molecular relaxations

Comparative dielectric studies of segmental mobility in novel polyurethanes

Characterization of the relaxation transitions in toluene diisocyanate-based polyurethanes with poly(propylene glycol) as the soft segment by thermally stimulated current depolarization with relaxation mapping analysis

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