Semi-rigid chains

FIG. 11 Adsorbed amount as a function of bulk concentration for a non-interacting (empty symbols) and adsorbing (full symbols) wall. Diamonds and triangles correspond to a system with semi-rigid chains, circles and squares for flexible chains [28]. 

FIG. 13 Average center-of-mass position of flexible chains of length / with respect to the nearest solid surfaces for different /. Diamonds denote a system of semi-rigid chains in which the opposite effect is observed [28]. 

On the other hand, as the width of a closed three-dimensional gap V is decreased, L(T>)) gradually decreases for absolutely flexible chains whereas for semi-rigid chains it goes through a minimum at D = 2 monomer diameters and then grows again for D = 1 (Fig. 15). 

Note Some polymers composed of semi-rigid chains form amphiphilic mesogens. Examples polyisocyanates and (2-hydroxyethyl)cellulose. 

B. Jingsheng, Y. Anji, Z. Shengqing, Z. Shufan and R Chang, Studies on the semi-rigid chain polyamide - poly(l,4-phenylene terephthalamide), J. Appl. Polym. Sci., 26 (1981) 1211-1220. 

It can be easily extended to disc-like molecules (de Gennes, 1973) that form a liquid crystal phase because of their anisotropic shape. The Onsager theory has also been extended to treat the poly-disperse polymer system (Parsons, 1979) and semi-rigid chain systems (Lekkerkeker et al, 1984). 

Finally we mention that draw-induced mesophases have also been observed in some other semi-rigid chain polymers. Examples of such studies are cold drawing of glassy PEN [108,109] and oriented crystallization of PET/PEN copolymers [110, 111]. In all cases a smectic mesophase has been reported. In the absence of crystallization it can attain a degree of stability that resists decay from chain relaxation. This supports the view that the mesophase represents a thermodynamic state [101]. We expect that similar mesophases based on semi-rigid monomers can be observed in other polymers with intrinsic rigid building blocks, such as other aromatic polyesters and polyamides. 

Poly(l,4-benzamide), abbreviated here as PpBA, was the first nonpeptide, synthetic condensation polymer reported to form liquid crystalline phases [11, 39,42,48-50]. Technologically important is poly(l,4-phenylene terephthalamide), abbreviated here as PpPTA. In both polymers the non-flexibility or semi-rigid chain structure is caused by the paralinked benzene rings and the partial double bond character of the carbon-nitrogen bond in the predominantly trans amide linkages. 

The scaling approach allows one to predict that the structure of an adsorption layer weakly depends on the volume concentration of polymer, if the adsorption energy is not too high. De Gennes emphasizes that the relationships derived are only valid for an equilibrium adsorption, which, however, can hardly be attained due to hindrance of the reorientation of chains, bonded to the surface. The concentration profile, 0(z), may also be estimated for semi-rigid chains near the solid wall. In this case, the chain is characterized by its persistent length, L, whereas the profile is determined by the value of Oq (z) obtained in the mean-field theory, accounting for the value L,0(z) = o(z + D). 

Nanocomposites Based on Semi-Rigid Chain Polymers (Polyimides)... 

Tatiana A. Shantalii - Senior researcher, Department of Polymer Thermophysics (DePTh), Institute of Macromolecular Chemistry, National Academy of Sciences of Ukraine. She graduated in Organic Chemistry from the Kuban State University (Krasnodar) and got her PhD (Polymer Chemistry) in the Institute of Macro-molecular Chemistry, National Academy of Sciences of Ukraine (1994). Area of research synthesis and structure-property relationships for semi-rigid chain polymers reinforced with the sol-gel derived inorganic nanophase. Publications over 30 papers in refereed journals. 

Due to its specialty in molecular chain structure, i.e., a semi-rigid-chain, the viscosity of PES is not very sensitive to changes in temperature or shear rate. Hence the flow performance cannot be increased effectively by shear rate or increases in barrel temperature and injection pressure. Since the SFL of PES is relatively low, it is difficult to mold parts with st histicated and thin-wall structures. 

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