P-Aromatic polyamides

Synthesis and Properties of p-Aromatic Polyamide Having Benzoxazinone... 

SYNTHESIS AND PROPERTIES OF p-AROMATIC POLYAMIDE HAVING BENZOXAZINONE UNIT IN THE MAIN CHAIN... 

Of the p-aromatic polyamides used to (voduce high-strength fibers, the simplest polyamide of symmetric and regular structure, PPTA, which has the most accessible and least expensive raw material base, occupies a special position. 

The successful development of polyfethylene terephthalate) fibres such as Dacron and Terylene stimulated extensive research into other polymers containing p-phenylene groups in the main chain. This led to not only the now well-established polycarbonates (see Chapter 20) but also to a wide range of other materials. These include the aromatic polyamides (already considered in Chapter 18), the polyphenylene ethers, the polyphenylene sulphides, the polysulphones and a range of linear aromatic polyesters. 

Fibers in which the basic chemical units have been formed by chemical synthesis, followed by fiber formation, are called synthetic fibers. Examples include nylon, carbon, boron fibers, organic fibers, ceramic fibers, and metallic fibers. Among all commercially available fibers, Kevlar fibers exhibit high strength and modulus. (Kevlar is a DuPont trademark for poly [p-phenylene diamine terephthalamide].) It is an aromatic polyamide (aramid) in which at least 85% of the... 

It is also possible to prepare them from amino acids by the self-condensation reaction (3.12). The PAs (AABB) can be prepared from diamines and diacids by hydrolytic polymerization [see (3.12)]. The polyamides can also be prepared from other starting materials, such as esters, acid chlorides, isocyanates, silylated amines, and nitrils. The reactive acid chlorides are employed in the synthesis of wholly aromatic polyamides, such as poly(p-phenyleneterephthalamide) in (3.4). The molecular weight distribution (Mw/Mn) of these polymers follows the classical theory of molecular weight distribution and is nearly always in the region of 2. In some cases, such as PA-6,6, chain branching can take place and then the Mw/Mn ratio is higher. 

Wertheimer, M.R. and Schreiber, H.P. (1981). Surfaee property modification of aromatic polyamides by microwave plasmas. J. Appl. Pnlym. Sei. 26, 2087-2096. 

Fully aromatic polyamides are synthesized by interfacial polycondensation of diamines and dicarboxylic acid dichlorides or by solution condensation at low temperature. For the synthesis of poly(p-benzamide)s the low-temperature polycondensation of 4-aminobenzoyl chloride hydrochloride is applicable in a mixture of N-methylpyrrolidone and calcium chloride as solvent. The rate of the reaction and molecular weight are influenced by many factors, like the purity of monomers and solvents, the mode of monomer addition, temperature, stirring velocity, and chain terminators. Also, the type and amount of the neutralization agents which react with the hydrochloric acid from the condensation reaction, play an important role. Suitable are, e.g., calcium hydroxide or calcium oxide. 

Fig. 1. Water flux and NaCl rejection of several membrane types (10), where (D) represents seawater membranes, which operate at 5.5 MPa and 25°C ( ), brackish water membranes, which operate at 1500 mg/L NaCl feed, 1.5 MPa, and 25°C and (SSI) nanofiltration membranes, which operate at 500 mg/L NaCl feed, 0.74 MPa, and 25°C. A represents cellulose acetate—cellulose triacetate B, linear aromatic polyamide C, cross-linked polyether D, cross-linked fully aromatic polyamide E, other thin-film composite membranes F, asymmetric membranes G, BW-30 (FilmTec) H, SU-700 (Toray) I, A-15 (Du Pont) J, NTR-739HF (Nitto-Denko) K, NTR-729HF (Nitto-Denko) L, NTR-7250 (Nitto-Denko) M, NF40 (FilmTec) N, NF40HF (FilmTec) O, UTC-40HF (Toray) P, NF70 (FilmTec) Q, UTC-60 (Toray) R, UTC-20HF (Toray) and S, NF50 (FilmTec). To convert MPa to psi,...

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. 

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. 

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

Palladium- or nickel-catalysed carbonylation polycondensation of dibromoar-enes with bifunctional nucleophilic monomers such as aromatic diamines and bisphenols in the presence of carbon monoxide appeared to be a new promising method for the synthesis of aromatic polyamides [scheme (15)] and polyesters [scheme (16)] respectively [162-170], The first successful example was the synthesis of high molecular weight polyaramide according to scheme (15) (Ar1 = m-C6H4-, Ar2 = p-C6H4 O C6H4 ) [162],... 

The features of initiation of free radical reactions in polymers by dimers of nitrogen dioxide are considered. The conversion of planar dimers into nitrosyl nitrate in the presence of amide groups of macromolecules has been revealed. Nitrosyl nitrate initiates radical reactions in oxidative primary process of electron transfer with formation of intermediate radical cations and nitric oxide. As a result of subsequent reactions, nitrogen-containing radicals are produced. The dimer conversion has been exhibited by estimation of the oxyaminoxyl radical yield in characteristic reaction of p-benzoquinone with nitrogen dioxide on addition of aromatic polyamide and polyvinylpyrrolidone to reacting system. The isomerisation of planar dimers is efficient in their complexes with amide groups, as confirmed by ab initio calculations. 

Aromatic polyamides and polyesters are examples of stiff chain polymers. Poly(p-phenylene terephthalamide) (Kevlar , 1-23) can be made by reaction (4-50) in a mixture of hexamethylphosphoramide and /V-methylpyrrolidone ... 

Relatively high solubility of PBLG in many solvents can be explained by the interaction of flexible side groups with solvents. On the other hand, for aromatic polyamides with p-structure, e.g. PPTA, the solubility is observed only for a very narrow range of solvents, mostly for concentrated acids (sulphuric, phosphoric, chlorosulphonic, hydrofluoric, and other acids). In this case the interaction of acid molecules with amide groups of a polymer reaches the energy of chemical reactions. 

We confined ourselves only to poly(y-benzyl-L-glutamate) and p-substituted aromatic polyamides, as most of experimental studies on phase equilibrium with the formation of liquid crystalline phase are based on the analysis of the behavior of these... 

It should be taken into account that in very rigid chains, such as those of poly-(alkyl isocyanate)s and para-aromatic polyamides, apart from rotation about valence bonds another mechanism can contribute to flexibility the deformation of valence angles and bonds during thermal chain motion just as it should occur in ladder structures (p. 100). When several flexibility mechanisms exist, the resulting rigidity of the homopolymer chain can be evaluated if the flexibilities, resulting from different mechanisms, are considered to be additive and the following equations are used ... 

High performance polymer fibers (HPPF) have excellent mechanical properties compared to traditional textile fibers such as nylon. The typical HPPFs are aramid and polyethylene fibers (6). Aramid is a generic name for a class of aromatic polyamide fibers, most of which are varieties of poly(p-pheny-lene terephthalamide). Kevlar is the trade name of the varieties of aramid polymers introduced conunercially by Dupont. The molecules in the fibers of these materials are oriented in the axial direction. Poly(p-phenylene terephthalamide) is a rigid molecule with the following structure ... 

M. Arpin and C. Strazielle, Characterization and conformation of aromatic polyamides poly(l,4-phenylene terephthalamide) and poly(p-benzamide) in sulphuric acid. Polymer, 18 (1977) 591-598. 

W. B. Black and J. Preston, Fiber-Forming Aromatic Polyamides in Man-Made Fibers, Science and Technology, Interscience, New York, 1968, Vol. 2, p. 297. 

Aromatic polyamides or aramids. The best known in the specialty fiber market are Nomex (poly-m-phenyleneisophthalamide) and Kevlar (poly-p-phenyleneterephthala-mide). 

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