Dielectric properties of segmented polytetramethyleneoxide‐based polyurethanes

Petrovìć, Zoran S.; Koco, Ferenc; Horváth, L.; Dulic, N.

doi:10.1002/app.1989.070381014

Cited by 8 publications

(2 citation statements)

References 13 publications

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“…We can compare the results obtained here with some other data on the dielectric behavior of polyurethanes (22)(23)(24)(25)(26)(27)(28)(29)(30). North and Reid (23) in an earlier contribution have distinguished electrode polarization and Maxwell-Wagner polarization mechanisms (due to phase heterogenity within the PUR polymer) at lower frequencies and ohmic conductivity and dipole orientation at higher frequencies.…”

Section: Discussionsupporting

confidence: 57%

Determination of unblended chain dynamic parameters of a polar discontinuous phase in an immiscible polymer blend

Havriliak¹,

Bánhegyi²,

Karasz³

1991

Polymer Engineering & Sci

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A method is described by which the relaxation characteristics of a polar polymer in an included phase of an immiscible polymeric blend can be determined from those of the composite. The necessary prerequisite is that the relaxation regions of the matrix and of the dispersed phase do not overlap. First, the dynamic relaxation data of the composite is fitted to the Havriliak‐Negami function using a multi‐response fitting method. Next, the relaxation function for the included phase is determined using composite mixing equations and the data for the pure matrix. This method is demonstrated for dielectric data on a polypropylene/polyurethane (PP/PUR) composite containing 20 wt% polar additive. The resulting unblended relaxation function parameters of PUR are discussed and compared to other unblended PUR literature data. Blending PUR with PP did not change the shape of the relaxation process, did shift the maximum frequency by about half a decade, and significantly reduced the limiting values of the dielectric constants.

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Section: Discussionsupporting

confidence: 57%

Determination of unblended chain dynamic parameters of a polar discontinuous phase in an immiscible polymer blend

Havriliak¹,

Bánhegyi²,

Karasz³

1991

Polymer Engineering & Sci

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“…[21][22][23] Complex dielectric spectra are to be expected for cross-linked polymers because both hard and soft phase can be either crystalline or amorphous. 24 . The behavior of the cross-linked polyurethanes can be compared with that of linear polyurethanes.…”

Section: Introductionmentioning

confidence: 99%

Dielectric properties of castor oil cross-linked polyurethane

Oprea¹,

Potolinca²,

Oprea

2010

High Performance Polymers

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A series of polyurethanes cross-linked with castor oil were synthesized and the influence of the polyurethane chemical structure on molecular relaxations in such systems was determined. Three different castor oil rates were used in the synthesis of the cross-linked polyurethane chains. These cross-linked polyurethanes were compared with a linear polyurethane which was obtained by chain extension with 1,4-butane diol. The dielectric properties and relaxation phenomena of the polyurethane were studied as a function of the hard segment structure and cross-linker content as structural variables and frequency and temperature as experimental variables. It was found that the formation of hydrogen bonds between urethane groups of physical networks may control the molecular mobility, but the chemical nature and content of the cross-links of the hard segments strongly influences the molecular relaxation. The relaxation peaks were observed in the temperature range of -65 to 60°C for polyurethane with different cross-linked segment contents, peaks which shifted to high temperature with the increase in frequency.

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Structural Studies and the Correlation with the Stress–Strain Response in Polyurethanes

Prisăcariu¹,

Scortanu²

2010

Encyclopedia of Analytical Chemistry

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The purpose of this article is to review and bring new contributions in understanding the relationship between molecular/supramolecular architecture at the nanometer scale and macroscopic mechanical properties in polyurethanes. In this article, this problem is addressed by studying numerous conventional segmented polyurethanes, based on several diisocyanates, macrodiols, and chain extenders. In order to widen the range of structures achievable beyond those normally available, in this review, we have also included recent developments that have been made in polyurethane materials by producing polymers based on isocyanates of variable geometry, giving hard segments that allow the variation of hard‐domain crystallinity as a key structural variable. They were used to probe the sensitivity of inelastic effects to structural details of the materials. Mechanical responses studied were large strain, constant strain rate, and cyclic strain responses, including interrupted tests. Results were related to microstructural changes, on the basis of evidence from small‐angle X‐ray scattering (SAXS) and wide‐angle X‐ray scattering (WAXS) and infrared (IR) dichroic measurements. Inelastic effects were most pronounced when the hard segment crystallized, and when the phase segregation was more pronounced. Thermal techniques such as differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used to study the thermal behavior of the materials. There were tendencies to phase separation, with a characteristic length of ca. 20 nm, and, when isocyanates of variable geometry were employed with certain chain extenders, to crystallization of the hard phase. Such materials display higher flow stress in the hard phase caused by stronger phase segregation. This has clearly revealed that inelastic features in the constitutive response of polyurethane elastomers are sensitive to microstructural detail on length scales of the order of nanometers. Hard‐domain crystallinity exerts a strong effect on inelasticity of the elastomers. There is a clear indication that the physical origin of the flow stress is the relative displacement of the hydrogen‐bonded hard segments. Inelasticity, as measured by hysteresis and unrecovered strain, was increased by increased phase separation.

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Dielectric properties of segmented polytetramethyleneoxide‐based polyurethanes

Cited by 8 publications

References 13 publications

Determination of unblended chain dynamic parameters of a polar discontinuous phase in an immiscible polymer blend

Determination of unblended chain dynamic parameters of a polar discontinuous phase in an immiscible polymer blend

Dielectric properties of castor oil cross-linked polyurethane

Structural Studies and the Correlation with the Stress–Strain Response in Polyurethanes

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