The dielectric and polarization behavior of polyurethane-based polycarbonate diols with different content levels of fluorinated hard segments

2021 ◽  
Author(s):  
Wannida Chunarrom ◽  
Hathaikarn Manuspiya
Keyword(s):  
Hysteresis Loop ◽  
Paraelectric Phase ◽  
Polarization Behavior ◽  
Hard Segments ◽  
Different Content

The addition of a fluorinated chain improved the polarization in polyurethane, shifted the relaxation peaks, and changed the hysteresis loop behavior from a ferroelectric to a paraelectric phase.

Correlation Between Electrocaloric Response and Polarization Behavior: Slim-Like and Square-Like Hysteresis Loop

2018 ◽  
Vol 215 (13) ◽  
pp. 1700971 ◽  
Author(s):  
Xin Nie ◽  
Shiguang Yan ◽  
Xuefeng Chen ◽  
Shaobo Guo ◽  
Fei Cao ◽  
...  
Keyword(s):  
Hysteresis Loop ◽  
Polarization Behavior

Corrosion. Anodic Polarization Behavior of Cr Carbide/Ni-Cr Composite Alloy.

1995 ◽  
Vol 44 (506) ◽  
pp. 1326-1331 ◽  
Author(s):  
Yasuyuki TAKATANI ◽  
Tomoki TOMITA ◽  
Kazumi TANI ◽  
Mitsuharu INABA ◽  
Yoshio HARADA
Keyword(s):  
Anodic Polarization ◽  
Composite Alloy ◽  
Polarization Behavior

Biodegradable Polyurethanes Cross-Linked by Multifunctional Compounds

2017 ◽  
Vol 14 (6) ◽  
pp. 778-784 ◽  
Author(s):  
Joanna Brzeska
Keyword(s):  
Polymer Structure ◽  
Cross Linking ◽  
Plant Oils ◽  
Lignocellulosic Materials ◽  
Soft Or ◽  
Native State ◽  
Synthetic Compounds ◽  
Multifunctional Compounds ◽  
Hard Segments ◽  
Synthetic Origin

Background: Cross-linking structure of polyurethanes determines no degradability of these materials. However, introducing the hydrolysable substrates (of natural or synthetic origin) into the cross-linked polyurethanes structure makes them biodegradable. Moreover compounds (such as polycaprolactone triol, glycerin, lysine triisocyanate, etc.) that are used for polyurethane cross-linking are degraded in non-toxic products. All these kinds of compounds can be introduced into soft or hard segments via urethane bonds. Objective: The review focuses on kind of multifunctional polyols and isocyanates, and low molecular crosslinkers used for cross-linked polyurethanes obtaining. These compounds are natural substrates (in the native state or after modification) or are synthetic compounds with degradable linkages. They belong to polyesters, plant oils, proteins, saccharides, and others (e.g. lignocellulosic materials), and they are synthesized chemically or via biosynthesis by algae, plants, microorganisms, and by animals. Conclusion: Incorporation of degradable groups (such as ester moieties) into the polymer structure, and using of substrates with the structure known and metabolized by microorganisms for soft or hard segments building, facilitate degradation of cross-linked polyurethanes.

Model reactions for the study of hydrogenation and acidic activity of palladium catalysts

1987 ◽  
Vol 52 (8) ◽  
pp. 2019-2027 ◽  
Author(s):  
Libor Červený ◽  
Nguyen Thi Du ◽  
Ivo Paseka
Keyword(s):  
Palladium Catalysts ◽  
Styrene Oxide ◽  
Side Reactions ◽  
Pd Catalysts ◽  
Variable Parameters ◽  
Acid Properties ◽  
Liquid Phase Hydrogenation ◽  
Acid Catalysed Reactions ◽  
Different Content ◽  
Model Reactions

Palladium catalysts have been used to study the hydrogenation of 1-phenyl-2-butene-1-ol which is accompanied by several side reactions considered to be acid-catalysed. Another model reaction studied was dehydration and subsequent hydrogenation or hydrogenolysis of 1-phenyl-1,3-propanediol to 3-phenyl-1-propanol, accompanied by formation of propylbenzene. The dehydration and propylbenzene formation can be again classified as acid-catalysed reactions. Another one is methanolysis of styrene oxide taking place under conditions of liquid phase hydrogenation due to the acid properties of Pd-H systems. Hydrogenation activity of Pd catalysts was tested by hydrogenation of cyclohexene. Sixteen Pd catalysts on different supports and with different content of active component were used, their activity and selectivity was determined and the effect of variable parameters in the synthesis of these catalysts on the activity and selectivity is discussed.

Miscibility and Crosslinking of Polybutadiene-Based Polyurethanes

2000 ◽  
Vol 65 (11) ◽  
pp. 1820-1832
Author(s):  
Miloslav Pekař ◽  
Pavel Kopecký
Keyword(s):  
Phase Structure ◽  
Initial Mixture ◽  
Cooperative Effect ◽  
Final Phase ◽  
Elastic Part ◽  
Hard Segments

Rheokinetics of polybutadiene-based polyurethanes was studied. Sixteen mixtures differing in the miscibility of reactive components and hard segments contents were prepared. Regardless of the miscibility of the components, the rheokinetics behaviour is qualitatively very similar. The viscous response part is formed and finished much earlier than the elastic part. The quantitative dissimilarities, caused by cooperative effect of miscibility and differences in reactivity, are described. Using a well miscible initial mixture need not give the best results as a reactive crosslinker can easily react with isocyanate and separate from the rest of the reaction mixture thus impairing the final phase structure.

scholarly journals PEG-POSS Star Molecules Blended in Polyurethane with Flexible Hard Segments: Morphology and Dynamics

Molecules ◽  
2020 ◽  
Vol 26 (1) ◽  
pp. 99
Author(s):  
Konstantinos N. Raftopoulos ◽  
Edyta Hebda ◽  
Anna Grzybowska ◽  
Panagiotis A. Klonos ◽  
Apostolos Kyritsis ◽  
...  
Keyword(s):  
Glass Transition ◽  
Star Polymer ◽  
Polymerization Process ◽  
Degree Of Crystallinity ◽  
Dielectric Relaxation Spectroscopy ◽  
Scanning Calorimetry ◽  
Similar System ◽  
Soft Phase ◽  
Hard Segments ◽  
Star Molecules

A star polymer with a polyhedral oligomeric silsesquioxanne (POSS) core and poly(ethylene glycol) (PEG) vertex groups is incorporated in a polyurethane with flexible hard segments in-situ during the polymerization process. The blends are studied in terms of morphology, molecular dynamics, and charge mobility. The methods utilized for this purpose are scanning electron and atomic force microscopies (SEM, AFM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and to a larger extent dielectric relaxation spectroscopy (DRS). It is found that POSS reduces the degree of crystallinity of the hard segments. Contrary to what was observed in a similar system with POSS pendent along the main chain, soft phase calorimetric glass transition temperature drops as a result of plasticization, and homogenization of the soft phase by the star molecules. The dynamic glass transition though, remains practically unaffected, and a hypothesis is formed to resolve the discrepancy, based on the assumption of different thermal and dielectric responses of slow and fast modes of the system. A relaxation α′, slower than the bulky segmental α and common in polyurethanes, appears here too. A detailed analysis of dielectric spectra provides some evidence that this relaxation has cooperative character. An additional relaxation g, which is not commonly observed, accompanies the Maxwell Wagner Sillars interfacial polarization process, and has dynamics similar to it. POSS is found to introduce conductivity and possibly alter its mechanism. The study points out that different architectures of incorporation of POSS in polyurethane affect its physical properties by different mechanisms.

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