Some features of chemical structure of the surface of fibres based on aromatic polyamides

Conclusions Under any heat treatment of fibres based on aromatic polyamides, the composition of their surface differs considerably from the stoichiometric. The presence of silicon-containing compounds, in our opinion, is a consequence of the technological fibre preparation processes.The discovered features of the chemical structure of fibres are apparently able to exert an important effect both on the physico-mechanical characteristics of the fibres themselves, and also on the processes of formation and degradation of an adhesive fibre-matrix bond in polymeric composites.Translated from Khimicheskie Volokona, No. 1, pp. 8–9, January–February, 1989.     

New aromatic silicon-containing polyamides

As part of an ongoing program to prepare and evaluate thermally-stable, processable materials, 18 aromatic, silicon containing polyamides (structures shown below) have been synthesized via interfacial polymerization of six silicon-containing diacid chlorides with 3,3′-diaminodiphenyl-nethane, 3,3′-diaminobenzophenone, and l-(3′-amino-benzy)-4-(3″aminobenzoyl)benzene. All polyamides were soluble in m-cresol and N,N-dimethylacetamide and had glass transition temperatures between 178 and 254°C, Thermogravimetric analyses conducted in static air on film specimens were-¹ used to show 5 and 10 percent weight losses between 331–400°C and 354–440°C, respectively. 3,3′- and 4,4′-silane isomers R = R′ = Me; R = Me; R′ = Ph; R = R′ = Ph     

Relaxation properties of aromatic polyamides

Conclusions Five relaxation transitions have been detected for PABI rigid-chain polymer by the method of dynamic mechanical losses, at 50, 140, 220, 380, and 480°C.An effect of relaxation transitions on the temperature dependence of strength has been demonstrated.Translated from Khimicheskie Volokna, No. 2, pp. 45–46, March–April, 1986.     

N-methylation of wholly aromatic polyamides for size-exclusion chromatography

Wholly aromatic polyamides, including poly(1,4-phenyleneisophthalamide) and poly(1,4-phenyleneterephthalamide) are N-methylated to render them soluble in N,N-dimethylformamide, a common size-exclusion chromatography eluent. The procedure N-methylates 50–55% of the total amide linkages in these two examples, permitting reproducible measurement of their absolute molecular weight distributions using differential viscometry detection. There is no observable degradation in molecular weight resulting from the N-methylation, provided the excess methylating reagent is destroyed shortly after completion of the derivatization by quenching with potassium acetate. The validity of the molecular weight data obtained by the method is confirmed by light-scattering measurements on derivatized polymer and by comparison to the molecular weight of underivatized polymer that can be approximated from the intrinsic viscosity in concentrated sulfuric acid. The method is applicable to a variety of wholly aromatic polyamide structures. Examples are given.     

Chlorination and oxidation of aromatic polyamides. I. Synthesis and characterization of some aromatic polyamides

The synthesis is described of some aromatic polyamides based on unsubstituted, and methyl-, carboxy-, and sulfo-substituted diamines by interfacial polycondensation. Some of them are crosslinked and some of them contain heterocyclic aromatic rings. Their chemical structures are characterized by IR and ¹³C solid-state NMR spectra and the spectra are interpreted. © 1996 John Wiley & Sons, Inc.     

The solubility parameters of aromatic polyamides

The degrees of swelling of rigid aromatic polyamide networks in various solvents, nonsolvents, and solvent mixtures were used to determine their solubility parameters. This was made possible because of the amorphous nature of the rigid networks and the low levels of intersegmental H-bonding. The solubility parameters are: δ = 23.0 (MPa)^1/2, δ_d = 18.0 (MPa)^1/2, δ_p = 11.9 (MPa)^1/2, and δ_H = 7.9 (MPa)^1/2. The determined values are believed to be good approximations of the solubility parameters of stiff linear aromatic polyamides, because of the essential identity of their structure and the stiff segments in the networks.     

Physicochemical characterization of some fully aromatic polyamides

The characterization of eight fully aromatic polyamides are described with the procedures required to yield film- and fiber-forming materials. Solutions of these aromatic polyamides in dimethylacetamide were characterized by NMR and the effects of dissolved lithium chloride on these spectra investigated. The NMR resonances for specific protons in these polymers are assigned. The IR spectra of thin films and fibers of these polyamides are also reported, together with glass transition temperatures as measured by differential scanning calorimetry (DSC). The value of NMR and IR to identify specific polyamide homopolymers and copolymers is discussed.     

改性聚芳酰胺的研究进展

聚芳酰胺是一类重要的高性能聚合物材料,因其突出的耐热性和力学性能被广泛应用于航空航天、交通运输、电子电气等领域。笔者综述了聚芳酰胺的改性途径及应用现状。     

Wet spinning of aliphatic and aromatic polyamides

Bench-scale equipment for wet spinning was designed and built. An experimental study of the wet spinning of several polyamides has been carried out. The polymers studied include nylon 6, nylon 66, redissolved Nomex, and redissolved Kevlar. The superstructure of the wet-spun fibers were studied by optical and scanning electron microscopy as well as small- and wide-angle x-ray diffraction. Mechanical properties were measured and related to the spinning variables. For nylon 6 and nylon 66, the coagulation bath composition was found to be of major importance in determining fiber superstructure. For the case of the redissolved Kevlar, anisotropic spinning dopes were obtained from redissolved fiber, and the wet-spun filaments produced from such solutions were investigated. These fibers proved to have relatively high modulus and strength as spun. They had even greater strengths after hot drawing.     

Creep of aromatic polyamide fibres

Creep of Kevlar 29, Kevlar 49 and PRD 49-III fibres was investigated. The fibres exhibited transient creep and the strain-time relationship was represented by a logarithmic time law. The creep strain recovered with time when the load was removed. Upon reloading to the same creep stress the strain-time relationship was again logarithmic but the creep rate was reduced. Modulus measurements were made during the creep test and these showed that the modulus increased with time. This result indicated a crystallite rotation mechanism which could account for the experimentally observed creep strain. Creep in PRD 49-III fibres exhibited a small temperature dependence over the temperature range 20°C to 150°C. The apparent creep activation energy was consistent with the range of values reported for hydrogen bonding. This suggests one possible creep mechanism in which the combined action of stress and thermal activation causes rearrangement of intercrystalline bonds in the crystallite boundaries resulting in boundary creep. Boundary creep allows crystallite rotation which produces the macroscopic creep strain. Boundary creep is discussed in terms of the fibre morphology and a model of delayed elasticity.     

Soluble aromatic polyamides bearing asymmetrical diaryl ether groups

A series of novel aromatic polyamides containing asymmetrical diaryl ether structure were synthesized by the phosphorylation polyamidation of 5-(4-aminophenoxy)-1-naphthylamine with various dicarboxylic acids. The polymers were obtained in high yields and moderately high inherent viscosities (0.74-1.36 dl/g). Except for one example, all the polyamides were amorphous and readily soluble in many organic solvents and could afford flexible and tough films via solution casting. The cast films exhibited good mechanical properties with tensile strengths of 90-128 MPa, elongations at break of 9-64%, and initial moduli of 2.08-3.08 GPa. Glass-transition temperatures ranged from 222 to 288 °C by DSC. Thermal stabilities by TGA for the polymer series ranged from 462 to 517 °C in air at the point of 10% weight loss. These polyamides displayed a lower crystallinity and better solubility and film-forming capability than the corresponding analogues derived from symmetrical 1,5-diaminonaphthalene and 1,5-bis(4-aminophenoxy)naphthalene.     

Organosoluble asymmetric aromatic polyamides bearing pendent phenoxy groups

This study focuses on the synthesis and characterization of new polyamides based on an aromatic asymmetric diamine‐containing phenoxy‐substituted benzophenone segment. Low‐temperature solution polycondensation reactions of this diamine with various aromatic diacid chlorides containing ether, hexafluoroisopropylidene or diphenylsilane groups resulted in polyamides with molecular weights in the range 102 900–113 200 g mol^?1. The structures of these monomers and the corresponding polymers were fully confirmed using elemental analysis and infrared and NMR spectroscopy. All polyamides were easily soluble at room temperature in polar aprotic solvents and even in less polar solvents such as tetrahydrofuran. The polymers showed excellent thermal stability, up to 385 °C, and displayed glass transition temperatures in the range 225–256 °C. All the polymers presented blue florescence upon irradiation with UV light and thus show promise for applications in electroluminescent devices. Copyright © 2011 Society of Chemical Industry     

N-Propargyl-substituted aromatic polyamides: preparation and thermal crosslinking

A series of high molecular weight aromatic polyamide copolymers derived from 4,4′-bis(methylamino)-diphenylmethane, 4,4′-bis(propargylamino)diphenylmethane and isophthaloyl dichloride was prepared as potential candidates for use as matrix resins in Kevlar^(R) fibre composites. These polyamides, which contain pendant propargyl groups, underwent facile crosslinking at 280°C as evidenced by dramatic increases in their glass transition temperatures (T_g) and accompanying loss of solubility. Other attempts to effect crosslinking by exposure to ultraviolet light, electron beam or gamma radiation were unsuccessful.     

Adhesive strength in the interaction of polyamides with aramid fibres

Wetting of organic fibres by polyamide melts was investigated. On the example of Terlon, it was shown that the contact angle of wetting increases in the order PA-610 < PA-6 < < PA-12. The polymers are also in the same order in wetting of a steel wire. Adhesion on the interface was investigated in the same systems. PA-610 in the form of powder exhibited maximum adhesion to steel wire and organic fibres. The necessity of using highly viscous matrices in the form of finely disperse systems for obtaining reliable and reproducible adhesive strength values was demonstrated. The validity of using steel wire as a model substrate was demonstrated and the qualitative characteristics of the change in the adhesive strength under the effect of factors which primarily alter the properties of the polymer matrix were found. The results obtained in studying the shear strength of the composites are correlated with the results of determining the adhesive strength in their unit cell. This allows recommending the shear method for evaluating adhesion in industrial conditions. Translated from Khimicheskie Volokna, No. 5, pp. 51–55, September–October, 1997.     

Preparation of structurally-colored aromatic polyamides and their physicochemical properties

Conclusions One-, two-, and three-stage methods of preparing structurally-dyed aromatic polyamides with chromophoric fragments in the chain have been investigated.It has been shown that the molecular weight of the polymers obtained and the proportion of chromophores bound into their chain is determined by the reactivity of the starting diaminoanthraquinones.It has been found that the introduction of anthraquinone units into the poly-m-phenylene isophthalamide chain has little effect on the structure or basic physicochemical properties of the polyamide, but gives the polymer a uniform and regular coloration.Structural dyeing of poly-m-phenylene isophthalamide with fragments of 1,5-DAAQ or 4,8-DADHAQ increases the resistance of the polyamide fibres to UV irradiation.The authors express their thanks to Yu. Ya. Shavarin and N. M. Bol'bit for performance of the fibre irradiation, and also to B. A. Tsaplin for thermomechanical testing of the fibres.L. Ya. Karpov NIFKhI, Moscow. VNIISV, Tver'. Translated from Khimicheskie Volokna, No. 2, pp. 24–27, March–April, 1992.     

Evaluating the defectiveness of yarns based on aromatic polyamides

Conclusions -- A procedure has been developed for evaluating the nonuniformity of elementary filaments in a cross section of a complex yarn.-- A procedure has been developed for estimating defectiveness and mean breaking tension of elementary filament from the results of testing the complex yarn.-- The procedures described can be used to evaluate the quality of yarns in optimizing the process of preparing them.Translated from Khimicheskie Volokna, No. 4, pp. 37–39, July–August, 1991.