Solution spinning aromatics

The electron spin resonance spectra were run in nitrogen-saturated solutions of aromatic compound ca. 10" m) and nucleophile (0-05-0-1 M) in the solvent(s) indicated. Irradiation in the cavity was effected with a high pressure mercury arc. Electrolysis was performed with the platinum cathode in the cavity, tetraethyl-ammonium perchlorate as electrolyte and electric currents of 10-250 /lA. 

The deuterium NMR spectra of toluene-d0 in aPS solutions consists of two resonances which are resolved and assigned to the methyl and aromatic groups. In these solutions spin-spin or dipolar couplings are small and consequently are not observed. As the temperature is lowered, the aromatic resonance systematically broadens while the methyl resonance remains relatively constant in width. The linewidths of the aromatic resonances are the same as those which would be predicted from the T2 measurements reported below. The separated resonances make it possible to determine the relaxation times of each type of resonance. 

For the above polymers, DuPont launched the commercial production of high-strength and high-modulus Kevlar libers and the Akzo Nobel corporation began production of Twaron libers. In the former, USSR scientists from the Fiber Research Instimte (Khimvolokno) synthesized high-modulus Terlon and Vmivlon fibers by fiber spinning from lyotropic solutions of aromatic copolyamides. Some mechanical properties of aromatic amides produced by different companies are presented in Table 4. °... 

In recent years, aliphatic/aromatic and aromatic polyamides have been developed. For example, the polymer obtained from HMD and terephthalic acid (Nylon 6,T) has a heat distortion temperature of 200°C. However because the is 370 °C, melt processing and spinning is not possible (decomposition results) and solution spinning from strong acids (H2SO4) must be used. Also interfacial polymerization (from the terephthaloyl acid chloride) is necessary to achieve high MWs. 

Due to the solidification of concentrated (spinning solutions of PPTA, they must be heated to 80-90X while processing into fib, which results in significant hydrolytic decomposition of the polymer in sulfuric acid. Copolyamides can be used instead of the homopolymer to decrease the or fluidity of solutions of aromatic polyamides. 

Technora. In 1985, Teijin Ltd. introduced Technora fiber, previously known as HM-50, into the high performance fiber market. Technora is based on the 1 1 copolyterephthalamide of 3,4 -diaminodiphenyl ether and/ -phenylenediamine (8). Technora is a whoUy aromatic copolyamide of PPT, modified with a crankshaft-shaped comonomer, which results in the formation of isotropic solutions that then become anisotropic during the shear alignment during spinning. The polymer is synthesized by the low temperature polymerization of/ -phenylenediamine, 3,4 -diaminophenyl ether, and terephthaloyl chloride in an amide solvent containing a small amount of an alkaU salt. Calcium chloride or lithium chloride is used as the alkaU salt. The solvents used are hexamethylphosphoramide (HMPA), A/-methyl-2-pyrrohdinone (NMP), and dimethyl acetamide (DMAc). The stmcture of Technora is as follows ... 

The primary driving forces behind investigation of new solvents include environmental concerns and the abiUty to form Hquid crystals in the new solvent systems. By analogy with Kevlar, a synthetic aromatic polyamide fiber, spinning from a Hquid crystalline solution should yield cellulose fibers with improved strength, as has been demonstrated in laboratory experiments. 

Yang and Jenekhe [186,187] reported a successful solubilization of aromatic polyimines in organic solvents via their soluble coordination complexes, which facilitated their solution characterization by NMR and processing films and coatings by spin coating and other techniques. This has created opportunities for various studies of the aromatic polyimines. 

Of particular interest in the application of cyclodextrins is the enhancement of luminescence from molecules when they are present in a cyclodextrin cavity. Polynuclear aromatic hydrocarbons show virtually no phosphorescence in solution. If, however, these compounds in solution are encapsulated with 1,2-dibromoethane (enhances intersystem crossing by increasing spin-orbit coupling external heavy atom effect) in the cavities of P-cyclodextrin and nitrogen gas passed, intense phosphorescence emission occurs at room temperature. Cyclodextrins form complexes with guest molecules, which fit into the cavity so that the microenvironment around the guest molecule is different from that in... 

Aromatic polyimide films that are spin-coated or solution-cast with thicknesses under 15 jm exhibit structural anisotropy in the condensed state. This anisotropy is associated with the tendency of the chains to align parallel to the substrate surface, undergoing what is described as in-plane orientation. 

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