Dielectric properties of polyamide-4,6

Journal of Polymer Science Part B: Polymer Physics, 1997

The mechanical and dielectric relaxation of a set of aromatic-aliphatic polyamides containing ether linkages have been examined as a function of temperature (0140 to 190ЊC) and frequency (3 to 10 6 Hz). The polymers differ in the orientation (meta and para) of the aromatic rings, in the length of the aliphatic chain, and in the number of ether linkages per repeating unit. Dynamic mechanical experiments showed three main relaxation peaks related to the glass transition temperature of the polymers ( a relaxation), the subglass relaxations associated to the absorbed water molecules ( b) and to the motion of the aliphatic moieties ( g). Dielectric experiments showed two subglass relaxation processes (b and g) that correlates with the mechanical b and g relaxations, and a conduction process ( s) above 50ЊC that masks the relaxation associated to the glass transition. A molecular interpretation is attempted to explain the position and intensity of the relaxation, studying the influence of the proportion of para-or meta-oriented phenylene rings, the presence of ether linkages and the length of the aliphatic chain.

Polymer, 1988

Poly(hydroxyethyl acrylate) presents two relaxation zones, labelled ~ and ~, when it is completely dry. The temperature of the maximum of the 7 relaxation, as well as its apparent activation energy, are somewhat higher than in poly(hydroxyethyl methacrylate), a fact that could be explained by higher intermolecular interactions in the series ofpolyacrylates than in the series ofpolymethacrylates. The absorption of even slight traces of water causes a new relaxation to appear, the intensity of which increases with the content of water, while at the same time the intensity of the 7 relaxation decreases. This fact suggests the formation of an association of the water molecules with the side groups of the polymer. The characterization of the relaxation is difficult because of the high d.c. conductivity component of the permittivity. Its temperature suggests the presence of hydrogen bonds which render the main chains rigid.

Applied Physics A, 2015

Polyimide co-polymers have been prepared based on different diamines as co-monomers: a diamine without CN groups and a novel synthesized diamine with two CN groups prepared by polycondensation reaction followed by thermal cyclodehydration. Dielectric spectroscopy measurements were performed and the dielectric complex function, ac conductivity and electric modulus of the co-polymers were investigated as a function of CN group content in the frequency range from 0.1 Hz to 10 7 Hz at temperatures from 25 to 260 °C. For all samples and temperatures above 150ºC, the dielectric constant increases with increasing temperature due to increaseing conductivity. The α-relaxation is just detected for the sample without CN groups, being this relaxation overlapped by the electrical conductivity contributions in the remaining samples. For the copolymer samples and the polymer with CN groups an important Maxwell-Wagner-Sillars contribution is detected. The mechanisms responsible for the dielectric relaxation, conduction process and electric modulus response have been discussed as a function of the CN groups content present in the samples.

Polymer International, 2012

The relaxation properties of polymethacrylates of the n-alkyl series with n = l, 2 and 4 (poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA) and poly(n-butyl methacrylate) (PnBMA)) have been measured and analyzed in order to relate their properties to the size of the lateral side chains. The n-alkyl series has been regarded as a model system and was used in this work to test a graphical data analysis method. Essentially, four relaxation processes were detected in the three polymers: the γ , β, α and αβ relaxations, in increasing order of temperature. It was found that the γ relaxation has a low activation energy, of around 36.3-38.5 kJ mol −1 , independent of the side chain, exhibiting low entropy of activation values when referring to the Eyring description of the activation parameters. The β relaxation was found to be similar in PMMA and PEMA, showing an activation energy of 88.8 kJ mol −1 , increasing to 112.8 kJ mol −1 in PnBMA. The activation entropy was also found to be low for this relaxation, although greater than that for the γ relaxation. In contrast, the α relaxation is quite different in these polymers. We observed a gradual shift in the glass transition temperature towards lower temperatures as the side chain increases in length. The manner in which the α transition makes its way into the dielectric spectra is more abrupt in PMMA than in PnBMA, denoting a higher fragility in the former polymer. Finally, there is a significant difference in the coalescence scenarios of the α and β relaxations for temperatures higher than the glass transition temperature, where they give rise to the so-called αβ relaxation.

Polymer International, 2019

Polyamide-6 (PA-6)/Boehmite Alumina (BA) nanocomposites were prepared via direct melt compounding. Structural, thermal and dielectric properties of "as received" (including moisture) and "dried" (thermally treated) specimens were examined. BA nanofiller was homogeneously dispersed into the PA-6 matrix. X-Ray Diffraction and FTIR spectroscopy revealed that crystallization of PA-6 in the γ-phase was favored over α-phase with increasing BA content. The Crystallinity Index (CI) and the percentage of α and γ phases were also evaluated. Dried specimens exhibited lower CI compared to the as received ones while CI decreased with the addition of the filler. Broadband Dielectric Spectroscopy revealed the presence of γ-, β-, α-relaxations, Maxwell-Wagner-Sillars effect and the contribution of Conductivity Relaxation in the as received samples. Drying procedure unmasked the double feature of both β-and α-modes. Results of the complementary techniques were analyzed and effects of moisture and/or the incorporation of BA nanofiller on the microstructure of the PA-6 matrix are disclosed.

Journal of Physics and Chemistry of Solids, 2007

The Maxwell-Wagner-Sillars (MWS) relaxation is studied for semi-crystalline polymers poly (ether ether ketone) (PEEK), in the range 20 Hz-1 MHz and temperature varying from 80 to 330 1C. The parameter is the crystallization condition in the case of PEEK, which is a semi-crystalline polymer considered as a particulate composite. The relaxation found in the semi-crystalline polymers above the a relaxation of the PEEK is ascribed to the trapping of conductive carriers at the interface between crystalline lamellae and the amorphous matrix. The study of PEEK microstructure is based on differential calorimetry and X-rays diffraction. Two lamellae populations have been detected, that depends on the crystallization temperature and its duration. The crystallinity rate is increasing with crystallization temperature and duration. In dielectric studies, the use of the electric modulus instead of permittivity allows us to minimize the ionic conduction and then leads to the appearance of the interfacial relaxation. According to our measurements, the crystallinity rate is not the main factor of the interfacial relaxation intensity, which also depends on the nature and degree of perfection of the lamellae. r

Polymer, 2007

Phosphate glass (Pglass)/polymer hybrids are a relatively new class of materials that combine the advantages of classical polymer blends and composites without their disadvantages. In the case of highly interacting Pglass/polymer (i.e., polyamide 6) hybrids, counter-intuitive properties that are difficult to explain are often observed. To shed light into the origins of the special behavior of the hybrids, we investigated the molecular relaxation processes in the hybrids using broadband dielectric spectroscopy. The dielectric loss spectra were fitted with the HavriliakeNegami equation and the characteristic relaxation times of the hybrid and the pure components were observed. The temperature dependence of the characteristic relaxation times was described using either the VogeleFulchereTammann, for the a-relaxations, or an Arrhenius type equation, for the band g-relaxations. The addition of Pglass greatly accelerated both the aand b-relaxations of the polyamide 6. However, the g-relaxation was found to be independent of Pglass composition. This suggests partial miscibility in the solid state, which was confirmed via NMR spectroscopy. The unexpected dramatic change in the b-relaxation process in the 10 vol.% Pglass hybrid suggests that blending can change the local environment of polyamide 6 due to the nanoscale morphology of this system as confirmed by TEM and NMR. It is thought that the fraction of miscible Pglass disrupts the hydrogen bonding between polyamide 6 chains and thereby reduces coordinated, multiple chain motion. In turn, this produces a plasticization effect and possible modification of the polyamide 6's crystalline structure in the Pglass/polyamide 6 hybrids.

The European Physical Journal E, 2017

High temperature polymeric materials for electrical insulation and energy storage are needed for transformational power applications such as pulsed-power and hybrid electrical vehicles. One of the candidate materials has been polyetherimide, an amorphous thermoplastic with a glass transition over 200 o C. Here, the dielectric studies on the material are reported by taking into account the polarization and conduction processes in the polyetherimide. The dielectric data were analyzed with the distribution of relaxation times approach with Debye expression as the kernel in the inversion algorithm, the results then created the relaxation map for polyetherimide. The method satisfies the Kramers-Kronig relationships, so the ohmic conductivity and permittivity at high frequencies could be estimated from the experimental data even there exists significant measurement error. The data were compared to the published results on polyetherimide in the literature. The materials is a low loss polymer with negligible ohmic losses below 200 o C. The estimated fragility of the polyetherimide was high about 284 from the resolved relaxation map using Vogel-Tammann-Fulcher expression. Polyetherimide is a good dielectric for advanced energy storage and electrical insulation technologies up to 200 o C.

A number of amorphous polyimides containing polar functional groups, cyano group, have been synthesized and investigated for potential use as high temperature piezoelectric sensors. The piezoelectric constants are related to the polarization. The remanent polarization and hence piezoelectric response of a material is determined by dielectric relaxation strength which is the difference in dielectric constant at the glass transition temperature vicinity. The intent of this work is to clarify the mechanism and key components required for developing piezoelectricity in amorphous polymers and further to apply this understanding in designing a unique high temperature piezoelectric polyimide. In this paper, experimental investigations of dielectric constant of piezoelectric cyano-substituted polyimides have been tested as a function of temperature to measure the dielectric relaxation strength in the glass transition temperature region.

Journal of Polymer Science Part B: Polymer Physics, 1993

The effect of structure on the sorption kinetics of water and of various organic solutes into polyimide (PMDA-ODA) thin films was studied. The major techniques employed include measurements of sorption kinetics, density, and dielectric relaxation. More solute uptake, lower densities and higher diffusivities were observed for films cured at lower temperatures. By measuring both changes of mass and of density, the volume expansion of the polymer due to each solute was obtained; this was found to be proportional to the molar volume of the solute. The two dielectric relaxation peaks (denoted by y1 and yz) due to water (and other solutes) were studied in detail to obtain the relevant activation energies and the separate dipole moments. While water and methylene chloride appear in both y1 and y2 configurations, methyl and ethyl alcohol appear mainly as yz, while acetic acid is primarily yl. It was concluded that the y1 configurations are relatively homogeneously distributed throughout the polymer, involving loose bonding to the polymer structure, while the y2 configurations involve small clusters, probably chains of molecules.

Journal of Molecular Structure, 2011

We report the chemistry of nanometer-sized spherical aramides nanoparticles and their copper complexes as novel types of hybrids nanomaterials. Based on the flexible linkage type, the average diameters of the nanoparticles-containing sulfone or ether linkage were 140 nm and 190 nm, respectively, as judged by the scanning electron microscopy (SEM) photographs. Incorporation of copper (II) ions into these particles furnished polymeric complexes in (1:2) ratios with square planar geometries. The polymeric structures were proved on the basis of their IR, UV, ESR and elemental analysis data. The thermal properties of the polymers were evaluated by various techniques and results revealed the high thermal stabilities of the hybrids. The calculated limiting oxygen index (LOI) indicates that such macromolecules can be classified as self-extinguishing polymers. The dc electrical conductivity of all samples indicates either semiconducting or metal-like nature in the regime of semiconductor behaviors. Incorporation of copper significantly improved the conductivity of the resulting complexes due to the enhanced mobility of the charge carriers upon doping. Dielectric losses are characterized by sharp peaks appearing at characteristic frequencies suggesting the presence of relaxing dipoles. The peak positions did not change with temperature indicating a non-activated process. The loss tangent increased with frequency and the peaks shifted toward the lower frequency upon doping suggesting the increase in the energy loss ratio compared to the energy storage in the dielectric. The higher value of dielectric loss at low frequency is due to the free charge motion within the materials. The reported dielectric results revealed anomalous behaviors which have not been reported earlier in similar hybrids.

Polymer, 2001

Dielectric behaviour of poly(2-norbornyl methacrylate) (P2NBM) and poly(3-methyl-2-norbornyl methacrylate) (P3M2NBM) was studied. The effect of the methyl substituent on the norbornyl ring is to decrease the temperature of the dynamic glass transition about 50 K. Moreover, weak secondary relaxations are observed in the two polymers under study. The secondary process of P3M2NBM has been conveniently analysed in terms of the empirical Fuoss±Kirkwood (F±K) equation.

Int J Basic Appl Sci, 2010

The scope of this work is to analyze the dielectric data obtained for the Poly (3hydroxy butyrate) PHB semi-crystalline polymer material in the view of the electric modulus formalism in order to correlate the effect of the conductive relaxation processes on the dipolar relaxation processes. The results reveal that the conductive relaxation processes contribution in the low frequency region is much larger than in the high frequency region. Finally plot of the imaginary part of the complex electric modulus for a given temperatures as a function of the real part of the complex electric modulus (i.e, Argand's plane) shows that the conductive processes are reflected by an arc at low frequency which agree with the model of Coelho.

Journal of Applied Polymer Science, 2018

A new grade of bio-based polyamide (PA)-PA meta-xylylene diamine 10 (PA mXD 10)-was investigated. Its first interest is that it permits mild processing conditions at about 200 C. The calorimetric study shows the existence of two cold crystallizations indicative of slow crystallization rate. The glass transition stabilizes at 55 C. By combining calorimetry with dynamic mechanical analysis and dynamic dielectric spectroscopy, we found a perfect consistency between the set of data giving the molecular mobility. The localized relaxations follow Arrhenius equations while the viscoelastic transition follows a Vogel-Fulcher-Tammann law. The compilation of all the relaxation times determined by means of the different analyses highlights a good correlation. This result is perfectly explained by the polarity of the macromolecular chain. The dynamic mechanical behavior showed a storage modulus higher than for the corresponding aliphatic PA and nearly constant until room temperature.

Journal of Non-Crystalline Solids, 2007

Thermally stimulated depolarization current experiments (TSDC) have been carried out on poly(dicyclohexyl itaconate) (PDCHI) in the glassy state. The polymer exhibits three relaxation zones in the interval of temperature studied: a d-relaxation at $130 K, a complex cprocess, in the temperature interval of 140 K to 200 K, and the b-process in the range of 210-270 K. The loss factor of PDCHI in the glassy zone has been reproduced from the partial depolarization data by using the elementary relaxation times and activation energies. The results show the existence of at least two relaxation processes in c-and b-zones. A tentative explanation of the molecular origin of the observed secondary relaxations has been done by means of molecular mechanics (MM). At this respect, we perform a comparison of the relaxational data of PDCHI and those corresponding to PCHMA. This comparison allows us to confirm the relevant role played by the cyclohexyl ring in the d-and c-relaxations.