Poly-para-phenylene terephthalamide

Liquid crystal aromatic polyamides (PARA), poly(meia-phenylene isophthalamide), Nomex , and poly(para-phenylene terephthalamide), Kevlar -49, were commercialized in 1961 and 1965, respectively. Amorphous aromatic polyamide, Trogamid , was introduced in 1969, and polyphthalamide Amodel in 1991. 

The para-aramids are typified by Kevlar (DuPont) and Twaron (Teijin) and are based on poly (para-phenylene terephthalamide) or PPTA. While having enhanced tensile strengths and moduli as a consequence of the extreme symmetry of their polymer chains and hence order or crystallinity, they also have improved thermal performance with a second order transition... 

Allen S R and Roche E J (1992) Tensile deformation and failure of poly(para-phenylene terephthalamide), Po/j/mer 33 1849-1854. 

Poly-para-Phenylene Terephthalamide (para-Aramld)... 

The inherent viscosities of the poiyaniiine base samples were determined at 25°C using solutions (0.1 wt.%) prepared in 97% sulfuric acid. In addition, a number of polyaniline samples of different inherent viscosities were analyzed by size-exclusion chromatography in concentrated sulfuric acid. Since the conformation and stiffness of polyaniline in sulfuric acid has not yet been determined, it is not possible to make direct correlations between the viscosity and the molecular weight. Instead, upper and lower limits of the molecular weights were estimated from comparison with viscosities measured under identical conditions of nylon 6 and poly-para(phenylene terephthalamide) and the Mark-Houwink relations [42,43] for these polymers. 

When the diamine and the dicarboxylic acid are attached to aromatic rings, the generic term for the polymers produced is aramide. The reaction of 1,4-diaminobenzene with tere-phthaloyl chloride gives poly(para-phenylene terephthalamide) (PPTA) marketed as Kevlar (Figure 21.23). Because of the extensive hydrogen bonding network between the chains (Figure 21.24), this is an extremely stiff material and has found wide applications in body armor and safety equipment. 

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 ... 

Poly(p-phenylene terephthalamide) PPD-T, also called para-aramid, can be polymerized to a fiber-forming molecular weight by polycondensation of terephthaloyl chloride and 1,4-phenylene diamine. 

Kevlar (Du Pont) and Twaron (Enka/Akzo) are trade names for the all para aramid, poly(p-phenylene terephthalamide), produced by these companies (Eq. 21.18). 

Depending on the modifications of poly-(p-phenylene terephthalamide) and analogous aromatic polyamides, it is possible to vary the solubility from concentrated sulfuric acid, to nonpolar aprotic solvents with inorganic salts, or to nonpolar aprotic solvents and to common organic colvents. In particular the incorporation of noncoplanar 2,2 -disubstitution has proven to remarkable enhance the solubility and lower the crystallinity. Gaudiana et al. [35] demonstrated that para-linked aromatic polyamides containing noncoplanar 2,2 -bis(trifluorome-thyl)biphenylene units are highly soluble in... 

Poly(p-phenylene terephthalamide)/PA or PARA, and PEKKorPAN Biphasic solution in sulfuric acid, spun, coagulated, stretched into PPD-T fibrils Cobum and Yang 1994... 

There are three types of major commercial aramid fibres in the market para-aramid (or p-aramid, poly-(p-phenylene terephthalamide), PPTA), meta-aramid (or m-aramid, poly-(meta-phenylene isophthalamides), MPIA) and co-polyamides fibres. 

Figure 4.1 represents the chemical structures of para-linked, poly(p-phenylene terephthalamide) (PPPT) and meta-linked, poly(m-phenylene isoph-thalamide) (PMPI) aromatic polyamides. These commercial aramids can be transformed into flame, cut-resistant, and high-tensile-strength synthetic fibers, which are widely used in the field of coatings. 

Aramid yarns (Kevlar of DuPont, Twaron of Teijin-Twaron) are produced from poly(p-phenylene terephthalamide), PPTA (2), which is specially developed for fiber spinning and not used in any other application. DuPont had experience with poly(m-phenylene isophthalamide) in a fiber product called Nomex for high-temperature applications. The polymer is produced in dimethylacetamide and the solution is dry-spun. This cannot be done with the stiff-chain para-para analogue PPTA. The polymer does not dissolve in organic solvents. A special polymerization route had to be developed, and the discovery of lyotropic behavior of concentrated solutions in sulfuric acid then led the way to the production of a magnificent new fiber material. 

In poly (p-phenylene terephthalamide), there are very stiff polymer chains and this is due to the bonding of rigid phenylene rings in the para position. The other advantage of PPTA is the presence of... 

Aramid is the name given to a class of polymers that are aromatic polyamides. The definition of an aramid fiber is a manufactured fiber in which the fiber forming substance is along chain synthetic polyamide in which at least 85% of the amide linkages are attached directly to two aromatic rings . There are various aramid fibers, including poly-m-phenylene isophthalamide known for its flame resistant characteristics (Dupont Nomex ). A second aramid is poly-p-phenylene terephthalamide developed by Akzo and DuPont, which consists of oriented para-substituted aromatic units. This makes polymer chains rigid and rodlike. 

Goto, T, Maeda, M. and Hibi, S. (1989), High-strength and high toughness aromatic polyamide fibre. I. Preparation and properties of block poly(para-phenylene and 4,4 -diphenyl ether terephthalamide) fibre. Journal of Applied Polymer Science. 37(4) jp. 867-875. 

The relative importance of the various factors determining the persistence length in solution and the conformation in the solid state of aromatic polyamides are well illustrated by the differences between the para and the meta forms of poly(phenylene terephthalamide). Both chains consist of the same planar elements, viz. the phenyl and amide groups. The latter group adopts only the trans conformation in these polymers, wherein the chance of a transition to the cis conformation is extremely small owing to a barrier of about 60-80 kJ mol Although in both para- and meta-linked chains the same intermolecular interactions exist between phenyl... 

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