Dielectric behaviour of isocyanate-terminated polymers
TL;DR: In this paper, the dielectric behavior of isocyanate-terminated polymers is reported as a function of frequency (100 Hz-100 kHz), temperature (30-90 degrees C) and the concentration of the curing agent, 4,4'-methylene bis(ortho-chloroaniline) (MOCA) (1.2, 3.5 and 4.7%) which was used in preparing the polymer from the toluene di-isocyanates and castor oil.
Abstract: The dielectric behaviour of isocyanate-terminated polymers is reported in this paper as a function of frequency (100 Hz-100 kHz), temperature (30-90 degrees C) and the concentration of the curing agent, 4,4'-methylene bis(ortho-chloroaniline) (MOCA) (1.2, 3.5 and 4.7%) which was used in preparing the polymer from the toluene di-isocyanate and castor oil. The dielectric constant and the loss were found to decrease as the MOCA concentration was increased. Distinct loss peaks were obtained. The influence of the curing agent on the dielectric properties of the polymer is discussed in detail. The most probable relaxation times were calculated from the complex arc plots of epsilon 'and epsilon ". From these arc plots it is established that the distribution of relaxation times becomes more and more symmetric with the increasing temperature. Activation energies were calculated. Maxwell-Wagner-Sillars interfacial polarisation is proposed as the probable mechanism.
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01 Jan 1986
TL;DR: In this article, the effects of temperature and cure on the dielectric properties of a sample subjected to a time-varying electric field are examined. And a selected bibliography of applications of dielectrics analysis to the study of thermoset cure is presented.
Abstract: All dielectric measurements involve the determination of the electrical polarization and conduction properties of a sample subjected to a time-varying electric field. Section 2 addresses dielectric measurement methods, the various instruments and electrodes, and their calibrations. Section 3 examines the microscopic mechanisms giving rise in the observed microscopic dielectric properties, and Section 4 explores in detail the effects of temperature and cure on these properties. Finally, Section 5 contains a selected bibliography of applications of dielectric analysis to the study of thermoset cure.
240 citations
14 citations
01 Jan 2012
TL;DR: This chapter deals with the importance, classification, materials and methods, modification, characterisation, curing, structure–property relationships and applications of vegetable oil-based polyurethanes.
Abstract: This chapter describes vegetable oil-based polyurethanes. It deals with the importance, classification, materials and methods, modification, characterisation, curing, structure–property relationships and applications of vegetable oil-based polyurethanes. The chapter also includes a short review of such polyurethanes from various vegetable oils. As polyurethanes are the most versatile polymers, exhaustive studies have been reported and more details of all aspects of their properties and uses are given. Vegetable oil-based polyurethanes are used in various fields from coatings to elastomers including smart biomaterials.
7 citations
TL;DR: In this paper, the effects of curing schedule and blend composition on their thermal, mechanical, and dielectrical properties of cured polycyanurate (PCN)/epoxy blend films are examined.
Abstract: In the study, polycyanurate (PCN)/epoxy resin (ER) blends are prepared to enhance the physical properties of cyanate ester resins. The effects of curing schedule and blend composition on their thermal, mechanical, and dielectrical properties of cured PCN/epoxy blend films are examined. FTIR analysis of the cured blend films exhibits the expected cyanurate and oxazolidinone peaks in all blend compositions except the film thermally treated for 1 h in the presence of 1% phenol. TGA results show that the thermal stability decreases with epoxy content in the blend film. From SEM analyses, it is observed that all films have very dense, smooth, and bubble free surface without phase separation. For the pure PCN, the dielectric constants are found to be 3.54–5.91 in the range of 10−1–107 Hz between 20°C and 200°C. PCN/epoxy blends up to 50% epoxy resin show a good stability of dielectric constant in this frequency band for 200°C, which is close to the dielectric constant of the homopolymerized PCN. Beyond this percentage of epoxy resin, dielectric constants of PCN/epoxy blends greatly increase at low-frequency region (0.1–103 Hz) due to the interfacial polarization governed by Maxwell–Wagner–Sillars effect. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers
5 citations
Journal Article•
TL;DR: Dielectric relaxation spectroscopy was used to examine molecular motion in polyurethane (PUR) derived from palm oil oleic acid-based polyols at room temperature and a g-relaxation process was proposed as the probable mechanism for the dielectric behaviour of PUR.
Abstract: Dielectric relaxation spectroscopy (frequency range from 100 Hz to 40 MHz) was used to examine molecular motion in polyurethane (PUR) derived from palm oil oleic acid-based polyols at room temperature. PUR was prepared by varying the oleic acid content in the polyol (28%, 40% and 65%), while the NCO/OH ratio of PUR was varied to 1.2, 1.4 and 1.6. The effect of chemical contribution on dielectric behaviour of the samples was described. Dielectric parameters were in the range of 2.0 to 3.0 for real permittivity e ’ and 0.02 to 0.08 for imaginary permittivity, e”. A Cole-Cole plot was fitted using the Havriliak-Negami model, and curvefitting simulations were performed using Origin software program. A g-relaxation process was proposed as the probable mechanism for the dielectric behaviour of PUR. The dielectric constant and loss mechanism of the material were dependent on the NCO/OH ratio and the percentage of oleic acid content in the polyols used in synthesising PUR. The frequency-dependent conductivity of PUR materials was analysed using a Jonscher’s power-law expression, and the plot exhibited a dc plateau and a frequency-dependent region.
4 citations
References
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TL;DR: In this paper, the locus of the dielectric constant in the complex plane was defined to be a circular arc with end points on the axis of reals and center below this axis.
Abstract: The dispersion and absorption of a considerable number of liquid and dielectrics are represented by the empirical formula e*−e∞=(e0−e∞)/[1+(iωτ0)1−α]. In this equation, e* is the complex dielectric constant, e0 and e∞ are the ``static'' and ``infinite frequency'' dielectric constants, ω=2π times the frequency, and τ0 is a generalized relaxation time. The parameter α can assume values between 0 and 1, the former value giving the result of Debye for polar dielectrics. The expression (1) requires that the locus of the dielectric constant in the complex plane be a circular arc with end points on the axis of reals and center below this axis.If a distribution of relaxation times is assumed to account for Eq. (1), it is possible to calculate the necessary distribution function by the method of Fuoss and Kirkwood. It is, however, difficult to understand the physical significance of this formal result.If a dielectric satisfying Eq. (1) is represented by a three‐element electrical circuit, the mechanism responsible...
8,409 citations
Book•
01 Jan 1971
TL;DR: The Science of Large Molecules POLYMERIZATION Step-Reaction (Condensation) Polymerization Radical Chain (Addition) PolyMERization Ionic and Coordination Chain (addition) Copolymerization Polymerisation Conditions and Polymer Reactions CHARACTERIZATION Polymer Solutions Measurement of Molecular Weight and Size Analysis and Testing of Polymers STRUCTURE and PROPERTIES Morphology and Order in Crystalline Polymers Rheology and the Mechanical Properties of Polymer Structure and Physical Properties as mentioned in this paper.
Abstract: The Science of Large Molecules POLYMERIZATION Step-Reaction (Condensation) Polymerization Radical Chain (Addition) Polymerization Ionic and Coordination Chain (Addition) Polymerization Copolymerization Polymerization Conditions and Polymer Reactions CHARACTERIZATION Polymer Solutions Measurement of Molecular Weight and Size Analysis and Testing of Polymers STRUCTURE AND PROPERTIES Morphology and Order in Crystalline Polymers Rheology and the Mechanical Properties of Polymers Polymer Structure and Physical Properties PROPERTIES OF COMMERICAL POLYMERS Hydrocarbon Plastics and Elastomers Other Carbon-Chain Polymers Heterochain Thermoplastics Thermosetting Resins POLYMER PROCESSING Plastics Technology Fiber Technology Elastomer Technology Appendixes Author and Subject Indexes.
1,703 citations
TL;DR: In this article, a dispersion region is observed in cobalt-zinc ferrites and barium ferrites, and the conductivity of these ferrites is explained by the hopping mechanism.
Abstract: DC conductivity and dielectric studies of CoxZn1−xFe2O4 (x = 0.32, 0.49, 0.79), BaFe12O19, and Mg0.25Zn0.75Fe2O4 are reported as a function of temperature and frequency. The lattice constant and the existence of a single phase are established from X-ray studies. The dielectric behaviour is attributed to the Maxwell-Wagner polarisation. A dispersion region is observed in one of the cobalt-zinc ferrites and the barium ferrite. Activation energies are calculated for these two ferrites from dielectric measurements. The conductivity of these ferrites is explained by the hopping mechanism. Activation energies and the transition temperatures are presented.
Ergebnisse von Gleichstromleitfahigkeits- und dielektrischen Untersuchungen an CoxZn1−xFe2O4 (x = 0,32; 0,49; 0,79) BaFe12O19 und Mg0,25Zn0,75Fe2O4 in Abhangigkeit von der Temperatur und Frequenz werden mitgeteilt. Die Gitterkonstante und die Existenz einer einzelnen Phase werden aus den Rontgenuntersuchungen festgestellt. Das dielektrische Verhalten wird der Maxwell-Wagner-Polarisation zugeschrieben. Ein Dispersionsbereich in einem der Kobalt-Zink-Ferrite und der Barium-Ferrite wird beobachtet. Fur diese beiden Ferrite werden aus den dielektrischen Messungen Aktivierungsenergien berechnet. Die Leitfahigkeit dieser Ferrite wird durch einen Hopping-Mechanismus erklart. Aktivierungsenergien und Ubergangstemperatur werden angegeben.
119 citations
TL;DR: In this article, the dielectric relaxation in polyethyl methacrylate has been studied over a wide range of frequency, temperature and pressure (up to 3000 atm). Three relaxation regions α, β and (αβ) were observed.
Abstract: The dielectric relaxation in polyethyl methacrylate has been studied over a wide range of frequency, temperature and pressure (up to 3000 atm). Three relaxation regions α, β and (αβ) were observed. The α relaxation moved rapidly to lower frequencies with increased pressure, whereas the β relaxation was quite insensitive in location to this variable. The (αβ) relaxation was split into α and β processes with increased pressure. The α relaxation in polyethyl acrylate moved rapidly and continuously to lower frequencies as pressure was increased.
The α, β and (αβ) relaxations are discussed in terms of molecular mechanisms. A comparison of dipole relaxations in the alkyl methacrylate series must be made with caution in view of the α and (αβ) relaxations which occur in these polymers.
116 citations
56 citations