Aramid repeat unit structure

The other major member of this grouping is the poly (aramid-arimid) fibre Kermel , which was produced initially by Rhone-Poulenc of France in 1971 and since 2007 has been an independent company, Kermel (France). It has the polymer repeat unit structure ... 

Aramid dendrimers Fully aromatic amide dendrimers 1,3,5-benzenetricarboxamide core 3,5-dicarboxamidophenyl repeat units phenyl or 3,5-dit-butyl isophthalate termini. Molecular modeling showed that the conformations of the isophthalate segment lead to the either open or conjested structure. [244]... 

Chain Packing and Crystal Structures. The chain packing and the suhmolecular arrangement of repeat units and pendant side groups of macromolecules in crystalline domains of polymers can be visualized using contact mode SFM. The resolution is in most cases not true resolution, since the area of the contact area (1 — few nm ) exceeds the molecular scale and must be considered lattice resolution instead. The first example of molecularly resolved structures of a polymer dates back to 1988, when Marti and co-workers reported on an SFM study on a polydiacetylene film (128). Examples for resolved chain packing and polymer crystal structure determination at the surface of semicrystalline polymers include poly(tetrafiuoroethylene) (PTFE) (129,130), polyethylene (PE) (131-133), polypropylene (PP) (134,135), poly(ethylene oxide) (PEO) (136), aramids (137,138), and poly(oxy methylene) (POM) (139). 

Nomex, another aromatic polyamide (compare aramid), is prepared by polymerization of 1,3-benzenediamine and the diacid chloride of 1,3-benzenedicarboxylic acid. The physical properties of the polymer make it suitable for high-strength, high-temperature applications such as parachute cords and jet aircraft tires. Draw a structural formula for the repeating unit of Nomex. 

Three examples of the above approach are given in Figs. 15-17. In Fig. 15 the experimental valence-band spectrum from a Kynol novoloid fiber [481 is compared with the spectrum calculated from an ab initio calculation using the polymer repeat unit. Figure 16 shows the calculated spectra for two components of the repeat unit in a Nomex aramid fiber, w-phenylenediamine and isophth-aldehyde if the compounds are combined they produce the predicted spectrum in Fig. 17b, which compares well with the experimental spectrum 48. Figure 18 shows the predicted spectra for oxidized carbon fibers using multiple. scattered wave Xa calculations on a set of substituted coronene units (25). The use of the band structure approach in polymers has been demonstrated in a study of polystyrenes [49]. 

Figure 16.10 Schematic representation of repeat unit and chain structures for aramid (Kevlar) fibers. Chain alignment with the fiber direction and hydrogen bonds that form between adjacent chains are also shown.

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