Poly- p-phenylene terephthalamide

Example 20. Poly(p-phenylene terephthalamide) by silylated diamines.33... 

Figure 16 Chain structure of poly(p-phenylene terephthalamide) (Kevlar ).

Poly(p-phenylene sulfide ketone), 23 709 Poly(p-phenylene terephthalamide),... 

As a consequence of this almost perfect alignment of molecule structures, such polyamides are able to orientate in solution and to form liquid crystalline phases (see Sect. 1.3.4). Out of these solutions one obtains fibers of poly(p-phenylene terephthalamide) (PPTA) having 5-10-fold higher values for stiffness and strength as the all-mefa linked polymers. In addition, PPTA crystallizes, whereupon the fibers achieve an extraordinary temperature resistance in a nitrogen atmosphere they decompose at temperatures above 550 °C without melting. 

These facts can be explained by a simple comparison of the stretched conformations of poly(p-phenylene terephthalamide) and poly(m-phenylene iso-phthalamide). Whereas the all-para linked polyamide can build up many hydrogen bonds to the neighboring molecules, this is less possible for the all-wcta linked polymer ... 

In concluding this section, we should touch upon phase boundary concentration data for poly(p-benzamide) dimethylacetamide + 4% LiCl [89], poly(p-phenylene terephthalamide) (PPTA Kevlar)-sulfuric acid [90], and (hydroxy-propyl)cellulose-dichloroacetic acid solutions [91]. Although not included in Figs. 7 and 8, they show appreciable downward deviations from the prediction by the scaled particle theory for the wormlike hard spherocylinder. Arpin and Strazielle [30] found a negative concentration dependence of the reduced viscosity for PPTA in dilute Solution of sulfuric acid, as often reported on polyelectrolyte systems. Therefore, the deviation of the Ci data for PPTA in sulfuric acid from the scaled particle theory may be attributed to the electrostatic interaction. For the other two systems too, the low C] values may be due to the protonation of the polymer, because the solvents of these systems are very polar. 

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... 

We compare Eq. (74) with the experimental results for two more stiff-chain polymers, PBLG and poly(p-phenylene terephthalamide) (PPTA). Since avail-... 

A major impetus was given to work, both academic and industrial, in the field of lyotropic systems by the development by duPont of commercial fibres having exceptionally high tensile strength and modulus through use of nematic anisotropic solutions of relatively rigid-chain aromatic polyamides. The earliest product to appear, Fibre B, was based upon poly (p-benzamide) (I)10), but was replaced by the fully commercial product, Kevlar, based upon poly (p-phenylene terephthalamide) (II) U). Arenka, from Akzo, also has the latter chemical repeating unit. 

These critical values differ from solvent to solvent. With the solvents most fully investigated, sulphuric acid for poly-(p-phenylene terephthalamide) and dimethyl acetamide/lithium chloride for poly (p-benzamide), there are also critical values of solvent composition the sulphuric acid must exceed a critical strength, the lithium chloride in the dimethyl acetamide must exceed a critical concentration. The critical values are, of course, interdependent rather than absolute. Diagrams that display some of the critical values for the two systems cited have been published in patents10,1 l Figures 3 and 4 illustrate the type of information available. 

Fig. 4. Phase diagram for solutions of poly (p-phenylene terephthalamide) in sulphuric acid74). Polymer inherent viscosity 3.32...

This section concentrates upon the development of materials based on aromatic polyamides, particularly poly(p-phenylene terephthalamide) (PPT) (II) u,7 l) and on poly(p-phenylenebenzobisthiazole) (PBT) (IV)75). These material, are primarily intended to satisfy the demands of industry for lightweight, high-performance hiaterials suitable for reinforcement purposes, especially in composites. The polymers have therefore been fabricated mainly into fibrous products. 

Poly(p-phenylene terephthalamide) (PPT) is usually synthesised 74 via a condensation reaction based on p-phenylene diamine and terephthaloyl chloride according to the equation shown in Fig. 6. 

They also studied the melting characteristics of the powders with surface-grafted MMA polymer by DSC [38]. Grafting of Kevlar 49, or poly(p-phenylene terephthalamide), fiber with GMA and AAm polymers without exposing to air was studied by Yamada et al. [39]. According to their grafting system, Kevlar yarn was suspended in an upper plasma-irradiation vessel and irradiated for 1 min at an Ar gas pressure of 20 Pa, an rf frequency of 13.56 MHz, and an rf power of... 

Nylon 6 is the homopolymer of caprolactam, and Kevlar is an aromatic polyamide, poly-p-phenylene terephthalamide. 

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