Dielectric Relaxation Studies of Segmented Polyesters

Lilaonitkul, Amnuey; Cooper, Stuart L.

doi:10.1021/ma60072a027

Cited by 23 publications

(5 citation statements)

References 7 publications

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“…For PBT, the y relaxation has been attributed to the local mode motions of the ester group in noncrystalline regions, while the y transition of the copolymers is believed to be a combination of the local motions of the tetramethylene oxide units of the soft segment and the y relaxation of the uncrystallized hard segments. 13 As the hard-segment concentration in the copolymer increases, there is a smooth transition of the ß relaxation to higher temperatures, and the experimental values are consistent with the predictions of the Fox-Flory expression if the fraction of crystalline material is accounted for. For the ß relaxation, activation energies (derived from Arrhenius plots) were found to vary from =67 to 32 kcal/mol with decreasing hard-segment concentration (from PBT to PEE-45) and from =13 to 10 kcal/mol for the y transition.…”

Section: Resultssupporting

confidence: 70%

Miscibility and cocrystallization in homopolymer-segmented block copolymer blends

Gallagher¹,

Zhang²,

Runt³

et al. 1993

Macromolecules

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The amorphous phase behavior of blends of poly(butylene terephthalate) (PBT) and polyester-ether) segmented block copolymers (PEE) was found to vary from completely immiscible to miscible, depending on the copolymer composition. The predictions of the Flory-Huggins relationship are in general agreement with the observed behavior when the interaction parameters are estimated from solubility parameters. The results of thermal analysis and small-angle X-ray scattering experiments strongly suggest that the PBT and PEE copolymers are capable of cocrystallization in the miscible blends under all crystallization conditions. The cocrystalline microstructure results from the complete miscibility and the blocky nature of the copolymer (i.e., the identical chemical and crystalline structures of the PEE hard segments and PBT). The crystallization rate of the copolymer in the miscible blends was found to be significantly enhanced due to the presence of PBT, and the resulting crystal thickness was found to be the same as that observed for PBT. Partially miscible blends of PBT with copolymers containing intermediate hard-segment concentrations formed distinguishable crystal populations, but the crystallization rate of the copolymer in these blends was also strongly influenced by the presence of PBT.

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Section: Resultssupporting

confidence: 70%

Miscibility and cocrystallization in homopolymer-segmented block copolymer blends

Gallagher¹,

Zhang²,

Runt³

et al. 1993

Macromolecules

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“…However, the reported activation energy for dielectric relaxation at glass transition of PTMO homopolymer is 154 kJ/mol (37 kcal/mo1). 22 The behavior of the PTMO soft segment in thermoplastic polyesters is not expected to be much different from that in polyurethanes except that hydrogen bonding is absent. Thus, the data of Lilaonitkul and Cooper could be used for comparison.22 They found that activation energy of the PTMO block (MW = 1000) glass transition increases from 154 to 249 kJ/mol as the hard segment concentration increases from 34 to 84 w t S. They also found that annealing decreases and absorbed water increases the activation energy of the p transition.…”

Section: Resultsmentioning

confidence: 99%

Dielectric properties of segmented polytetramethyleneoxide‐based polyurethanes

Petrovìć¹,

Koco²,

Horváth³

et al. 1989

J of Applied Polymer Sci

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SynopsisThree series of segmented polyurethanes, based on polytetramethylene oxide (PTMO) soft segments, having molecular weights of 650, l(j00, and 2000 and MDI/butane diol hard segments, were synthesized and their dielectric properties examined. The effect of the soft segment length, soft segment concentration (ssc) as structural variables, and frequency and temperature as experimental variables, on relative permittivity and tan6, were examined. The results were discussed in terms of the structural parameters such as the degree of phase separation and soft segment phase state. It was found that both soft segment length and ssc strongly affect dielectric behavior. INTRODUCTIONSegmented polyurethanes are a class of block copolymers, consisting of alternating "hard" and "soft" blocks.'-5 Due to the immiscibility of the blocks, phase separation takes place. The morphology of these two-phase systems varies with soft segment concentration (ssc) from a continuous hard phase with a dispersed soft phase (at low ssc) to a continuous soft phase with dispersed hard domains (at high SSC).~ Intermediate morphology, with both phases continuous, is found at about equal concentrations of the two phases? Soft segments are usually made of polyether or polyester chains having molecular weights between lo00 and 3000, while the hard segment usually consists of a diisocyanate and short chain diol or diamine, called "chain extender." The properties of segmented polyurethanes can be varied across a wide range, by varying soft segment length, ssc, and chemical structure of both segments. One of the important features of these polymers is that their mechanical behavior can be varied from the nylonlike, at low ssc, to the soft rubberlike, a t high ssc.Hard domains in the soft phase play the role of physical crosslinks, allowing high elastic (reversible) deformations. Polyurethane elastomers are advanced materials with many applications in various fields. Thus, the study of property-structure relationships is of great scientific and practical importance. I t has been found, however, that the degree of phase separation is determined

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“…Low-frequency polarizations in segmented polyetheresters have been studied by North et al27 and by Lilaonitkul and Cooper. 28 Both groups attributed the process to the polarization of free space charge in a multiphase medium, where one or more phases exhibits significant steady-state electrical conductivity. Due to an early reference to the process by J. C. Maxwell (1892) and elaboration by K. W. Wagner (1914), the process has become known as the Maxwell-Wagner loss process.…”

Section: /(Q)mentioning

confidence: 99%

Microstructure in linear condensation block copolymers: modeling approach

Vallance¹,

Cooper²

1984

Macromolecules

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X-ray scattering, differential scanning calorimetry, and dielectric spectroscopy have been combined to model the microstructure in linear thermoplastic condensation block copolymers where one block is semicrystalline. The materials characterized were segmented polyether-esters which exhibit properties between those of elastomers and tough plastics. Quantitative analysis of experimental data was used to evaluate a set of explicit modeling assumptions, regarding the nature of the crystalline and amorphous phases as well as the nature of the interdomain boundaries. The data generally supported the modeling assumptions of sharp interfaces between phase domains, minimal disorder in the polyester crystallites, nearly complete mixing of the chemically dissimilar sequences in the amorphous domains, predominantly three-dimensional (rather than one-dimensional) organization of the crystal-amorphous superstructure, and decreased self-diffusion among the amorphous sequences immediately adjacent to the (001) surfaces of the polyester crystallites. Microstructural parameters such as phase composition, crystallite size, and intercrystallite distance statistics were determined from the modeling studies. Subaudio frequency dielectric spectroscopy appears to be a useful technique for investigating interdomain boundary zone properties. Certain questions remain unresolved, such as to what extent is the crystalline phase continuous.

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Dielectric Relaxation Studies of Segmented Polyesters

Cited by 23 publications

References 7 publications

Miscibility and cocrystallization in homopolymer-segmented block copolymer blends

Miscibility and cocrystallization in homopolymer-segmented block copolymer blends

Dielectric properties of segmented polytetramethyleneoxide‐based polyurethanes

Microstructure in linear condensation block copolymers: modeling approach

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