Spinning reaction

Reaction spinning of monomers or prepolymers can be used to form fibers from reactive starting materials. One good example for reaction spinning is the formation 

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To produce a spandex fiber by reaction spinning, a 1000—3500 molecular weight polyester or polyether glycol reacts with a diisocyanate at a molar ratio of about 1 2. The viscosity of this isocyanate-terrninated prepolymer may be adjusted by adding small amounts of an inert solvent, and then extmded into a coagulating bath that contains a diamine so that filament and polymer formation occur simultaneously. Reactions are completed as the filaments are cured and solvent evaporated on a belt dryer. After appHcation of a finish, the fibers are wound on tubes or bobbins and rewound if necessary to reduce interfiber cohesion. 

Reaction spinning equipment is quite similar to that of solution wet spinning. It differs principally in the use of fewer wash baths and in the use of belt-type dryers instead of heated cans. 

Stability of diradicals is important for photochemical reactions. Spin multiplicity of the ground states is critical for the molecular magnetic materials. The relative stability of singlet (triplet) isomers and the spin multiplicity of the ground states (spin preference) [48] has been described to introduce the orbital phase theory in Sects. 2.1.5 and 2.1.6. Applications for the design of diradicals are reviewed by Ma and Inagaki elsewhere in this volume. Here, we briefly summarize the applications. 

Nitroso compounds, nitrones, and other diamagnetic molecules are used as spin traps. Capturing radicals prodnced in the reaction, spin traps form the so-called spin adducts—stable nitroxyl radicals easily detectable by ESR spectroscopy. In other words, the progress of the reaction can easily be followed by an increasing intensity of the spin-adduct signal. By and large, the method of traps reveals radicals by the disappearance (or appearance) of the ESR signal. 

Sensitivity to the magnetic held strength has also been observed in the process of photoisomerization of tran -stilbene (tS) into c -stilbene (cSt) in the presence of pyrene (P). The reaction was run in a solution with acetonitrile, DMSO, or hexafluorobenzene being a solvent. During the reaction, spin polarization was established (Lyoshina et al. 1980). The spin polarization was explained by the following sequence of the elementary acts ... 

Diffusion-Controlled Reactions, Spin-Satistical Factors in (Saltiel and Atwater). 

All-p-phenylene oxadiazole/N-methyl hydrazide copolymers have yielded high performance fibers with tenacities of 18-21 gpd and moduli above 300 gpd through an unconventional polycondensation reaction of terephthalic acid, dimethyl terephthalate and hydrazine sulfate in fuming sulfuric acid and subsequent "reaction spinning" into aqueous acid. 

Fibers (6) of p-phenylene oxadiazole/N-methyl hydrazide copolymers were prepared by polymerization of terephthalic acid (TA), dimethyl terephthalate (DMT) and hydrazine sulfate in fuming sulfuric acid (Oleum) and "reaction spinning" of the resulting polymer solution into aqueous sulfuric acid. Replacement of some of the dimethyl terephthalate used with dimethyl isophthalate (DMI) allowed the preparation of p-/m-phenylene oxadiazole/ N-methyl hydrazide copolymers. In the polymerization, a p-/m-phenylene oxadiazole polymer is formed which is methylated during the reaction ... 

During the "reaction spinning" process, the methylated oxadiazole units are hydrolyzed to mono-methylated hydrazide linkages yielding fibers of the p-/m-phenylene oxadiazole/N-methyl hydrazide copolymers ... 

For this reason, the process is termed reaction spinning. Details of the spinning process have been disclosed. Since the spinnerets and other devices are in contact with concentrated F12S04, they must be made out of acid resistant materials. ... 

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