Search results for "liquid"

1995

Redoxactive liquid crystalline (LC) side group polymers were prepared by copolymerization of liquid crystalline acrylates and ferrocene-containing acrylates. The corresponding liquid crystalline ionomers were synthesized by a reversible redox reaction. The incorporation of tetra-alkylated ferrocene derivatives leads to LC polymers with reduced redox potential. These polymers can be oxidized under mild conditions to the corresponding ionomers, which are much more stable in solution than LC ionomers containing monoalkylated ferrocenium ions. Dynamic mechanical measurements and small angle X-ray scattering (SAXS) perfomed on LC ionomers prove the existence of ionic superstructures (clusters) w…

1996

Combined LC-polymers possess the structural properties of both LC main chain and LC side chain polymers. Beneath this structural speciality, their broad LC-phases and their polymorphism (different smectic phases and one nematic phase as a function of temperature) make them interesting. Crucial to an understanding of them is the fact that main chain and side chain mesogens orient parallel to each other and interact cooperatively to form the LC-phase. Due to this synergism the temperature range of the LC-phase is much broader than that of the corresponding LC main chain and LC side chain polymers. This interplay of main chain and side chain mesogens allows structures to be designed with prefe…

Rheological behavior and thermal stability of poly(phenylene sulfide)/vectra-B950 blends

1994

Blends of polyphenylene sulfide (PPS) with a commercial, wholly aromatic, liquid crystalline polymer (LCP), Vectra-B950, have been prepared by melt-blending. Their rheological behavior has been studied in order to determine if the LCP displays a processing aid ability, and under what conditions it gives rise to potentially reinforcing fibrils dispersed in the PPS matrix. The problem of the thermal stability of PPS/LCP blends, which has been considered by some authors as the main obstacle to the production of usable materials due to the evolution of gaseous substances during processing, has been discussed. © 1994 John Wiley & Sons, Inc.

Effects of filler type and mixing method on the physical properties of a reinforced semirigid liquid crystal polymer

1996

Semirigid liquid crystalline polymers (LCPs) show some advantages with respect to rigid LCP: in particular lower processing temperatures, better compatibility with flexible thermoplastics, but also some disadvantages. Thermal resistance of rigid LCPs is much better and the maximum working temperature is, in general, very high. The thermomechanical properties can be improved by adding inorganic fillers. In this work processing, mechanical and thermomechanical properties of a filled semirigid liquid crystal copolyester are reported. Several inorganic fillers have been used in order to put in evidence the influence of shape and dimensions of the particles on the properties of the filled materi…

Rheological behavior of a semirigid liquid crystal polymer

1993

The rheological behavior of liquid crystal polymers is still far from completely clarified from both experimental and theoretical points of view. In this paper, the shear flow and the non-isothermal elongation flow behavior of a semi-rigid liquid crystal copolyester is discussed. The viscosity strongly decreases when the test temperature is increased above the crystal-nematic transition temperature; below this temperature the viscosity is very high. The thermal history strongly affects the shear viscosity. The elongational flow behavior depends also on temperature. Above the crystal-nematic transition temperature and the mesophase is easily spinnable, whereas below this temperature, the spi…

Processing and characterization of blends of fluoroelastomers with semirigid liquid crystal polymers

1996

Fluoroelastomers (FEs) usually have working temperatures above 150°C and a great resistance to aggressive agents such as oils, fuels, aliphatic and aromatic solvents, steam, moderate acid, and basic environments. Liquid crystal polymers (LCPs) can be effective processing aids and reinforcing agents for elastomers. These characteristics are very attractive to lower melt viscosity and to stiffen and strengthen the final product through a simple blending. Among the LCPs, the semirigid LCPs seem the most appealing for blending with flexible thermoplastics (FTs) because their processing temperatures can be arranged to be in the same processing temperature range of FTs and because the presence of…

Highly cross-linked imidazolium salt entrapped magnetic particles – preparation and applications

2012

Magnetic particles entrapped into highly cross-linked imidazolium salts were synthesized using a straightforward approach by radical polymerization of bis-vinylimidazolium salts in the presence of superparamagnetic iron oxide particles. Potential applications for these new materials as (i) catalysts for conversion of propylene oxide to propylene carbonate, (ii) supports for organocatalysts, and (iii) scavenger materials for palladium removal are outlined.

1982

The electro-optical properties of liquid crystalline polymers with polar mesogenic units in the side chain were investigated. It could be shown, that in an electric field, they show all effects known from low molecular weight liquid crystals, e.g. the Freedericksz-transition, the DAP-effect, the formation of William's domain, and the dynamic scattering. The optical response times are slightly longer than for low molecular weight liquid crystals, but in some cases at higher temperatures as short as 200 ms. By comparison of different polymers and some corresponding liquid crystalline monomers, it is found that: (1) the difference between the measuring temperature and the glass transition temp…

THERMOTROPIC HOMOPOLYESTERS. IV. STUDY OF FIBER FORMATION.

1983

We report a melt spinning and viscosity study of two semiflexible homopolyesters containing both rigid and flexible segments in the repeating unit. Single filaments of the polyesters formed from 4,4′-diacetoxybiphenyl and azelaic acid (PB7) and sebacic acid (PB8), and from 4′-hydroxyphenyl-4-hydroxycinnamate and azelaic acid (C7), were spun at temperatures between 205 and 255°C. The temperature dependence of the Newtonian melt viscosity of PB7 and C7 was investigated, and a range of molecular weights was studied for PB7. The spinning parameters, fiber characteristics, and viscosity-temperature behavior are related to the type of mesophase formed. The mechanical properties of fibers spun fro…

Visible polarized light transmission spectroscopy of the electro-optic switching behaviour of surface stabilized ferroelectric liquid crystal cells

1991

Abstract We present in this paper an experimental and theoretical modelling study of the switching characteristics and electro-optic behaviour of chevron surface stabilized ferroelectric liquid crystal cells with planar (low pre-tilt) and non-planar (high pre-tilt) surface conditions. The visible polarized light transmission spectra were taken of the cells with glass plates coated with films of either rubbed polymer or obliquely evaporated silicon monoxide (SiO) at various applied voltages and in various stages of switching and compared with the theoretical values calculated numerically based on our director-polarization structure model for the aforementioned cells. The results provide evid…