Amorphous nylon chemical structure

Amorphous nylons are transparent. Heat-deflection temperatures are lower than those of filled crystalline nylon resins, and melt flow is stiffer hence, they are more difficult to process. Mold shrinkage is lower and they absorb less water. Warpage is reduced and dimensional stability less of a problem than with crystalline products. Chemical and hydrolytic stability are excellent. Amorphous nylons can be made by using monomer combinations that result in highly asymmetric structures which crystallize with difficulty or by adding crystallization inhibitors to crystalline resins such as nylon-6 (61). 

The chemical structure of a polymer determines whether it will be crystalline or amorphous in the solid state. Both tacticity (i.e., syndio-tactic or isotactic) and geometric isomerism (i.e., trans configuration) favor crystallinity. In general, tactic polymers with their more stereoregular chain structure are more likely to be crystalline than their atactic counterparts. For example, isotactic polypropylene is crystalline, whereas commercial-grade atactic polypropylene is amorphous. Also, cis-pol3nsoprene is amorphous, whereas the more easily packed rans-poly-isoprene is crystalline. In addition to symmetrical chain structures that allow close packing of polymer molecules into crystalline lamellae, specific interactions between chains that favor molecular orientation, favor crystallinity. For example, crystallinity in nylon is enhanced because of... 

Fig. 1. Chemical structures of barrier polymers, (a) Vinylidene chloride copolymers (b) hydrolyzed ethylene—vinyl acetate (EVOH) (c) acrylonitrile barrier polymers (d) nylon-6 (e) nylon-6,6 (f) amorphous nylon (Selar PA 3426), y = x + 2 (g) nylon-MXD6 (h) poly(ethylene terephthalate) and (i) poly(vinyl...

The chemical structure of another amorphous nylon is shown in Fig. 8.64. The tertiary hutyl group attached to the amine molecule is bulky and disrupts this molecule s ability to crystallize. This particular amorphous nylon is sometimes designated as Nylon 6-3-T. Amorphous polymers can have properties that differ significantly from... 

Amorphous nylon Copolymer PA that have no crystallinity in their polymer structure. These materials offer strength and performance similar to other nylon materials, while also providing high transparency (i.e., they are clear). Compared to other clear (amorphous) resins, they offer advantages such as excellent dimensional stability and good chemical resistance. Applications include displays, safety equipment, and medical devices. 

As regards the general behaviour of polymers, it is widely recognised that crystalline plastics offer better environmental resistance than amorphous plastics. This is as a direct result of the different structural morphology of these two classes of material (see Appendix A). Therefore engineering plastics which are also crystalline e.g. Nylon 66 are at an immediate advantage because they can offer an attractive combination of load-bearing capability and an inherent chemical resistance. In this respect the arrival of crystalline plastics such as PEEK and polyphenylene sulfide (PPS) has set new standards in environmental resistance, albeit at a price. At room temperature there is no known solvent for PPS, and PEEK is only attacked by 98% sulphuric acid. 

PEBA exhibit a two-phase (crystalline and amorphous) structure and can be classified as a flexible nylon. Physical, chemical, and thermal properties can be modified by appropriate combination of different amounts of polyamide and polyether blocks [149], Hydrophilic PEBAs can be prepared which can have specific applications in medical devices. Similarly to other thermoplastic elastomers, the poiyamide-based ones find applications in automotive components, sporting goods conveyor belting, adhesives, and coatings [150]. In recent years the world consumption was approximately 6400 tons per year with about 80% in Western Europe and the rest equally split between the United States and Japan [143],... 

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