Semirigid polymers

With regards to crystallinity, aromatic polyimides are recognized as semirigid polymers that can crystallize in many instances, and, in fact, crystallinity has been reported for many polyimides. They can spontaneously crystallize when the chemical structure and the synthesis method are favourable, or they can develop crystallinity after an appropriate thermal treatment [65,66,74,75]. 

It should be expected that the influence of the chain segment mobility is most pronounced when the photochrome groups are inserted into a semirigid polymer backbone instead of being attached as mobile side groups in copolymers. Therefore, polyesters have been prepared by condensation of bis-hydroxymethyl-spirobenzopyrans with bisacid dichlorides.followed by polyesterification with bisphenol-A43,46). Thus, a photo-chromic poly(bisphenol-A-pimelate) (polyester XI) of the following formula was obtained. 

A distinctive feature of semirigid polymers such as p-aramids is that their solutions develop molecular orientation under shear or extension with great ease. This results in a unique difference in properties in the direction of shear or extension vs. those perpendicular to the shear direction. There are two classes of materials that have this characteristic lyotropic, which form anisotropic solutions and thermotropic, which form anisotropic melts. As aramids do not melt we will focus here on lyotropic systems. Anisotropic solutions differ from isotropic solutions in many physical characteristics including light depolarization, rheological properties, phase behavior, and molecular orientation. 

If in a mixture of a lyotropic polymer in a solvent, we replace the solvent partially by a flexible polymer with preferential affinity for the solvent, segregation leads to enclosures of concentrated semirigid polymers. The transition temperature is consequently relatively high (fig. 9). 

This great variety of rigid or semirigid polymers opens a wide field for the creation of new polymers by combining them with EPs. Combining here means producing a blend. Such a blend may be a phase... 

Thermoreversible gelation of rigid rod-like and semirigid polymers... 

Biopolymers by Guenet [3], which have been primarily concerned with thermoreversible gels in flexible polymer systems. The present review will focus on thermoreversible physical gels formed from rigid rod-like and semirigid polymers. 

Pam-linked aromatic LC polyesters are semirigid polymers which are typically thermotropic. Although it has only rarely been mentioned in the literature, thermoreversible gelation is a general observation for LC polyesters. An initial study on the thermoreversible gelation has been performed on the polyester shown in Figure 13.6 [48]. 

Are just simple entanglements responsible for the thermoreversible gelation of rigid or semirigid polymers which becomes predominant at a certain stage of the solvent quality or is it really the formation or ordered structures which drives the formation of thermoreversible gelation The answer to these questions requires more data on solution... 

Semirigid Polymer Gels for Size Exclusion Chromatography... 

A wide variety of commercial semirigid polymer gels exist for both organic and aqueous SEC. Following the introduction of smaller particle size packings. 

Belenkii et al. reported in 1975 (8) the SEC of PVP with unspecified molecular weight using Pharmacia Sephadex G-75 and G-lOO columns and a 0.3% sodium chloride solution as the mobile phase. Deviations from universal calibration behavior were noticed from PVP, dextran, polyethylene oxide (PEG), and polyvinyl alcohol. With the development of the important semirigid polymer gel, Toyo Soda TSK-PW columns for water-soluble polymers, Hashimoto et al. reported in 1978 (9) the SEC of PVP K-30 and K-90 using TSK-PW 3000 and two 5000 columns an 0.08 M Tris-HCl buffer (pH =... 

Cytochrome c dissolved in a film of polyethyleneoxide (PEO) or polyacrylamide (PAA) and immobilized at the surface of carbon electrode in this way yields a well-defined cyclic voltammogram (Fig. 16). The parameters of the electrode process are almost identical to those of the process in an aqueous medium. This finding can be apparently related to a high content of water in the gel. This system can be used in investigations of electron transfer properties of semirigid polymers suitable for constructing biosensors and to study solid-state enzyme catalysis. [221]. 

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