Polyamides, Fibers

Abstract

Polyamide fibers are melt‐spun from linear thermoplastic polymers having recurring amide groups made from diamines and dicarboxylic acids or lactams. Polymer made by the polycondensation of hexamethylenediamine and adipic acid is designated nylon‐6,6; that made from ε‐caprolactam, nylon‐6. These polymers account for about 98% of the total 3.9 million tons of worldwide production of nylon fiber. The attributes of nylon fiber, such as high strength, durability, abrasion resistance, resilience, ease of dyeability, and low specific gravity, have been recognized since its introduction in 1938. Both the inherent properties and those properties that can be engineered into the fiber through manufacturing and ultimately into the fabric article in downstream mill processing account for the diverse end uses of nylon. These include hosiery, lingerie, skiwear, activewear, swimwear, carpets, tire cord, luggage, upholstery, automotive air bags, interliners, and military uniforms. Nylon fiber is manufactured by extruding molten polymer through a filter pack multihole spinneret assembly and then drawing (or stretching) the filaments as a separate or continuous process to fix the size and physical properties (tenacity, elongation modulus) of the filaments (or yarn) for a particular end use. The product is offered as continuous flat yarn or, through additional manufacturing steps, as crimped staple, tow, or precision‐cut flock. Continuous‐filament (flat) yarn can be used as is, or, for most applications, textured for bulk and/or stretch. Physical appearance, functionality, and performance of nylon filaments can be modified by incorporating additives, eg, delusterants, colorants, antioxidants, and antistats, in the polymer or directly to the melt stream prior to extrusion, by designing a spinneret hole to impart a desired luster or surface effect or by spinning bicomponent or biconstituent fibers. Very fine fibers (0.2 dtex = 0.18 den), are made by spinning biconstituent conjugate fibers with nylon and polyester and dissolving the polyester in an alkali fabric treatment. The introduction of direct melt‐spun 0.88–2.22‐dtex (0.8–2.0 den) nylon products in the mid‐ to late‐1980s had a significant positive effect on the apparel market. Other breakthrough technologies, such as high speed spinning of partially oriented yarns for draw texturing, nylon‐4,6 for industrial yarn applications, soil‐ and stain‐resistant nylon carpets, utilization of available 47–93‐tex (420–840‐den) industrial yarns for an emerging automotive air bag industry, have all contributed to the growth of nylon fibers since the 1980s. The commitment made by the textile industry to recycle fibers and fabrics and to conserve materials and minimize landfilling in compliance to regulatory legislation will have a profound effect on how fiber producers design their offerings for the future.

Enantioselective construction of quaternary N-heterocycles by palladium-catalysed decarboxylative allylic alkylation of lactams

“…Nitrogen-containing heterocycles are ubiquitous in natural products, i pharmaceuticals, ii and materials science. iii , iv , v Stereoselective methods for the synthesis of 3,3-disubstituted pyrrolidinones, piperidinones, and caprolactams, in addition to the corresponding amines, are valuable for the preparation of a wide array of important structures in these areas of research ( Figure 1 ). Despite the prevalence of such architectures and the potential of lactam enolate alkylation as a direct method for their synthesis, a paucity of enantioselective lactam alkylations leading to C(α)-quaternary centers are known.…”