Dielectric properties liquid crystalline polymers

Optical and electro-optical behavior of side-chain liquid crystalline polymers are described 350-351>. The effect of flexible siloxane spacers on the phase properties and electric field effects were determined. Rheological properties of siloxane containing liquid crystalline side-chain polymers were studied as a function of shear rate and temperature 352). The effect of cooling rate on the alignment of a siloxane based side-chain liquid crystalline copolymer was investigated 353). It was shown that the dielectric relaxation behavior of the polymers varied in a systematic manner with the rate at which the material was cooled from its isotropic phase. 

Dielectric and Electrooptical Properties of a Chiral Liquid Crystalline Polymer... 

The unique capabilities of solid-state deuteron NMR (as well as experiments with N and result from the ability to assess ordering and mobility of individual bonds in a solid material. One can specifically examine the molecular mechanisms that determine bulk properties. This ability has motivated deuteron studies of such fundamental issues as the nature of the glass-transition [10-18] interactions in blends and mixtures [19-26], the molecular ordering and dynamics of crystalline materials [10,11,27-31] dynamics of elastomers [32-45], dielectric properties [46,47] and mechanical spectroscopy [48-51]. New experiments continue to be tied to methods development, particularly in the areas of multi-dimensional NMR [10,11,46, 52-61]. Recently, deuteron NMR has been employed in the characterization of new materials, for example for new liquid crystalline polymers [62-84],... 

Thermotropic liquid crystalline polymers (TLCPs) have gained increased commercial attention because of their unique properties. These include their low coefficients of thermal expansion, low viscosity, and high modulus, low permeability to gases, low dielectric constants, and chemical resistance. As the demand for these characteristics increases, it is anticipated that the use of TLCPs will grow, rising at a projected annual growth rate of 25 % from an estimated use of ten million pounds in recent years. In expanding the potential uses for TLCPs, it has been found that TLCP/TLCP blends can possess characteristics which are better than those of either individual TLCP (Utracki and Favis 1989). But the better result is only possible if the LCP fibrillation is prominent in the blend system. 

In the present account we shall not seek to duplicate the detailed accounts of the dielectric properties of polymers contained in the texts of McCrum, Read and Williams, Hedvig and Jonscher or in the reviews by Williams. Instead we shall give a structured account which incorporates the recent developments in experimental techniques and theoretical interpretations and gives illustrations of representative dielectric behaviour for selected amorphous, crystalline and liquid crystalline polymers, and for polymers in solution. 

In this review the material has been selected to illustrate the main features of the dielectric properties of solid polymers in their amorphous, partially crystalline and liquid crystalline states and of polymers in solution. It should be apparent that the dielectric method provides a powerful and... 

Sin Sinh, L. H., Son, B. T., Tmng, N. N., Lim, D.-G., Shin, S. H., Bae, J.-Y. Improvements in thermal, mechanical, and dielectric properties of epoxy resin by chemical modification with a novel amino-terminated liquid-crystalline copoly (ester amide). Reactive Ftmctional Polym. 72 (2012) 542-548. 

Of these featores, the pressure-dependence of SCF properties dominates or influences virtually every process conducted on polymers. Pressure governs such properties as density, solubility parameter, and dielectric constant changes of more than an order of magnitude are common when pressure is sufficiently increased to transform a gas into a supercritical fluid. This chapter primarily compiles experimental data on the pressure dependence of physical properties of fluid phase polymer-SCF mixtures. Phase equilibria are addressed, including the solubility of polymers in SCFs, the solubility of SCFs in liquid polymers, and the three-phase solid-fluid-fluid equilibria of crystalline polymers saturated with SCFs. Additional thermodynamic properties include glass transition temperature depressions of polymers, and interfacial tension between SCF-swollen polymers and the SCF. The viscosity of fluid phase polymer-SCF mixtures is also treated. 

Pfeiffer, M., Beresnev, L. A., Haase, W., Scherowsky, G., Kuehnpast, K., and Jung-bauer, D., Dielectric and electrooptic properties of a switchable ferroelectric liquid crystalline side chain polymer. Mol. Cryst. Liq. Cryst., 214, 125-141 (1992). 

M. PCeilfar, L. A. Bresncv. W. Haase, O. Scberawald, K. Kflhnpaai. and K. Jungbauer, Dielectric and electro-optic properties of a sariicbable ferroelectric liquid crystalline side-diain polymer. MoL Cryst fiq. Crysi 214 125 (1992). 

An alternative method to observe dielectric properties is termed thermal stimulated currents (TSC). This method involves polarization of a sample at high temperature (relative to Tg) and quenching to a temperature where depolarization is kineticaUy prevented in the time scale of the experiment. The temperature is then increased and the depolarization current is measured, yielding peak values associated with polymer transitions analogous to t", E" and tan S values obtained by conventional dielectric and dynamic mechanical measurements. The TSC spectra can reveal secondary relaxations, glass transitions and liquid or crystalline phase transitions and hquid crystalhne phase transitions. TSC has been applied to PBT/PC and PA6/ABS blends to study the intermixing of the components of the respective blends [58]. The TSC method is described in several references [59-61]. 

It is evident from these studies that dielectric relaxation spectroscopy provides a direct and unambiguous method for studying the molecular dynamics and alignnient properties of liquid crystalline side chain polymers. It has the distinct advantage over the NMR, ESR and DSC methods that a wide frequency range (10 to 10 Hz) can be covered at each temperature in the liquid crystal, biphasic and isotropic ranges of these anisotropic materials. 

Monomer 12 is a crystalline solid which, when homopolymerized, affords a high Tg, thermally stable polymer that has potential application in both the microelectronic and aerospace areas. Monomer 13 (mixed isomers) is a liquid at room temperature and, when homopolymerized, also provides a high Tg, thermally stable polymer that has a low moisture uptake and a low dielectric constant. This polymer has been targeted into the microelectronics area because of this interesting set of properties, combined with the prepolymer s unique ability to planarize over underlying topography. 

The high dielectric constant is characteristic of hydrogen-bonded liquids. Since HF forms only a two-dimensional polymer, it is less viscous than water. In the vapor, HF is monomeric above 80°C, but at lower temperatures the physical properties are best accounted for by an equilibrium between HF and a hexamer, (HF)6, which has a puckered ring structure. Crystalline (HF) has zigzag chains (Fig. 2-1). 

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