Flexible polymers dielectric properties

Nonlinear Electro-optic and Dielectric Properties of Flexible Polymers... 

We have shown in this paper the relationships between the fundamental electrical parameters, such as the dipole moment, polarizability and hyperpolarizability, and the conformations of flexible polymers which are manifested in a number of their electrooptic and dielectric properties. These include the Kerr effect, dielectric polarization and saturation, electric field induced light scattering and second harmonic generation. Our experimental and theoretical studies of the Kerr effect show that it is very useful for the characterization of polymer microstructure. Our theoretical studies of the NLDE, EFLS and EFSHG also show that these effects are potentially useful, but there are very few experimental results reported in the literature with which to test the calculations. More experimental studies are needed to further our understanding of the nonlinear electrooptic and dielectric properties of flexible polymers. 

Samples of one polymer, prepared from 4,4 -biphenol, appeared to have good mechanical flexibility and toughness as well as good dielectric properties. This polymer was prepared in sufficient quantity to allow a more extensive evaluation of the polymer properties, including thermal, mechanical, and dielectric properties. Results of the tests are listed in Table 3.2. 

Investigations in the past years have proved that applying the concept of flexible spacer, polymers can be synthesized systematically, which exhibit the l.c. state. Owing to the flexible linkage of the mesogenic molecules to the polymer main chain, very similar relations can be expected with respect to 1-l.c., like chemical constitution and phase behavior, or dielectric properties and field effects for the l.c. side chain polymers. This will be in contrast to main chain polymers, where the entire macromolecule, or in case of semiflexible polymers parts of the macromolecules, form the l.c. structure. The introduction of a flexible spacer between backbone and mesogenic group can be performed in a broad variety of chemical reactions. Some arbitrarily... 

Several papers compare the properties of sulfobetaine (meth)acrylic polymers. NMR spectra and solution properties of 23a and 23b [59,60] are correlated with data from the corresponding polycarbobetaines [26]. The photophysical and solution properties of pyrene-labeled 23c were studied in terms of fluorescence emission. Addition of surfactants induces the formation of mixed micelles in aqueous solution [61]. Excluded volume effects of the unlabeled polymer were measured by light scattering [62], its adsorption on silica was studied by adsorbance measurement and ellipsometry [62,63], and the electrostimulated shift of the precipitation temperature was followed at various electric held intensities [64]. Polysulfobetaines may accelerate interionic reactions, e.g., oxidation of ferrocyanide by persulfate [65]. The thermal and dielectric properties of polysulfobetaines 23d were investigated. The flexible lateral chain of the polymers decreased Tg, for which a linear relationship with the number of C atoms was shown [66,67]. 

Entanglements of flexible polymer chains contribute to non-linear viscoelastic response. Motions hindered by entanglements are a contributor to dielectric and diffusion properties since they constrain chain dynamics. Macromolecular dynamics are theoretically described by the reptation model. Reptation includes fluctuations in chain contour length, entanglement release, tube dilation, and retraction of side chains as the molecules translate using segmental motions, through a theoretical tube. The reptation model shows favourable comparison with experimental data from viscoelastic and dielectric measurements. The model reveals much about chain dynamics, relaxation times and molecular structures of individual macromolecules. 

Bruma et al. prepared several poly(amide imide sulfone)s [140] and investigated the thermal and dielectric properties of the polymers. The fluorinated polymer as shown in Scheme 3.10 had the lowest Tg, 279 °C, which resulted from the combined effects of meta-structures with the highest amount of flexible bridges, -SO2- and -0-, per repeat unit of the macromolecule. The dielectric constants of polymer films were in the range 3.49, close to the dielectric constant (3.2) of Kapton. This shows that introduction of hexafluoroisopropylidene units into the main chain does not significantly affect the electrical properties probably both amide and sulfone groups, which are polar, were also present in the macromolecule. 

The preparation of polyimides with magnetic filler content as humidity sensor devices represents a new research area. Because aromatic polyimides are more frequently utilized in sensing technology due to their excellent mechanical and thermal properties or radiation resistance (Sroog 1991) as well as their favorable thermal stability and dielectric properties (Hu et al. 2009), the development of new, more flexible polyimides requires different strategies. In order to increase the solubility of polyimides, two structural modifications of the polymer chain were proposed ... 

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