Molecular weight distribution liquid crystallinity

Viscoelasticity is one of the important mechanical properties of blended materials. Viscoelastic behaviour is the intermediate character between liquid and solid states that combines the viscous and elastic responses under mechanical stress. When a force is applied to blended materials, they can flow in the same as being liquids. The natural rubber blended materials do not stretch, but they will only gradually return to their original shapes when the force is released. This property depends on temperature, pressure, time, chemical composition, molecular weight, distribution, branching, crystallinity, and the composite of blending conditions and systems. ... 

Using IR spectroscopy and NMR, one can analyze the chemical structure of PA. The molecular weight and molecular weight distribution can be analyzed by endgroup analysis, viscometry, and high-pressure liquid chromatography (HPLC). The crystalline order can be analyzed by WAXS, small-angle X-ray spectroscopy... 

Block copolymers with PS and a polymethacrylate block carrying a liquid crystalline group, PS-b-poly 6-[4-(cyanophenylazo)phenoxy]hexyl methacrylate, were successfully prepared in quantitative yields and with relatively narrow molecular weight distributions (Scheme 5) [18]. The thermotropic liquid crystalline behavior of the copolymers was studied by differential scanning calorimetry. 

The zero-shear viscosity r 0 has been measured for isotropic solutions of various liquid-crystalline polymers over wide ranges of polymer concentration and molecular weight [70,128,132-139]. This quantity is convenient for studying the stiff-chain dynamics in concentrated solution, because its measurement is relatively easy and it is less sensitive to the molecular weight distribution (see below). Here we deal with four stiff-chain polymers well characterized molecu-larly schizophyllan (a triple-helical polysaccharide), xanthan (double-helical ionic polysaccharide), PBLG, and poly (p-phenylene terephthalamide) (PPTA Kevlar). The wormlike chain parameters of these polymers are listed in Tables... 

Liquid crystallinity can be attained in polymers of various polymer architectures, allowing the chemist to combine properties of macromolecules with the anisotropic properties of LC-phases. Mesogenic imits can be introduced into a polymer chain in different ways, as outhned in Fig. 1. For thermotropic LC systems, the LC-active units can be connected directly to each other in a condensation-type polymer to form the main chain ( main chain liquid crystalline polymers , MCLCPs) or they can be attached to the main chain as side chains ( side chain liquid crystalline polymers , SCLCPs). Calamitic (rod-Uke) as well as discotic mesogens have successfully been incorporated into polymers. Lyotropic LC-systems can also be formed by macromolecides. Amphiphihc block copolymers show this behavior when they have well-defined block structures with narrow molecular weight distributions. 

Synthesis. The main demand for the synthesis of this new type of liquid crystalline polymer is a high conversion and the absence of any side reactions for both reaction steps. For the first investigations described in this communication IR-spectroscopy was used to determine the conversion. The molecular weight distribution obtained from gel permeation chromatography (GPC) is used to monitor side reactions. 

The two-step synthesis process shown in Figure 2 affords several possibilities for preparing new side-chain liquid crystal polymers. The polymerization process allows one to vary the molecular weight and molecular weight distribution (MWD), and potentially change the properties of the liquid crystalline state. Most of the polyphosphazenes reported in the literature, including the examples in this paper, are derived from the bulk uncatalyzed process this... 

Living polymerizations in which initiation is fast and quantitative and which have irreversible growth offer several advantages over conventional polymerizations. In addition to the ability to obtain polymers with controlled molecular weights and narrow molecular weight distributions, it is also possible to control the polymer architecture and chain end functionality. For example, diblock and triblock copolymers containing liquid crystalline blocks have been prepared by living polymerizations. 

Owing to high viscosity, broad molecular weight distribution, existence of poly-crystalline and amorphous material, the liquid crystalline nature of thermotropic polym.ers is usually established through a combination of these methods. 

The resulting polymers show liquid crystalline behavior, good solubilities, and molecular weight distributions. Furthermore, the polymers display a blue emission. It has been suggested that such... 

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