Polyamides, aliphatic Nylon

Tension Above materials plus High-density polyethylene Polypropylene Acetal polymers Aliphatic polyamides (nylons) PPO Poly(ethylene terephthalate) Polysulphones... 

Likewise, the Tm values of aromatic polyamides (aramids) arc higher than those of the corresponding aliphatic polyamides (nylons). The Tm of monadic and dyadic nylons decreases as the number of methylene groups in the chain increases. Thus the Tm values decrease stepwise as the number of... 

FIGURE 3.4 Structure of (a) aliphatic polyamides (nylon-x and nylon-x-y) and (b) polyacrylamide. 

Bulte AMW, FoUters B, Mulder MHV, and Smolders CA. Membranes of semicrystalUne aliphatic polyamide nylon 4,6 Formation by diffusion-induced phase separation. J. Appl. Polym. Sci. 1993 50(l) 13-26. 

Polyamides are obtained either by the condensation of a dicarboxylic acid and an alkylene diamine or by the head-to-tail condensation between an amino carboxylic acid or the corresponding lactam. Polyamides may have aliphatic or aromatic chain backbones. Aliphatic polyamides (nylon) have the most important commercial applications, mainly in the manufacture of fibres. Nylon-6 and nylon-6,6 account for around 85% of all nylon currently used. Nylon-6 is derived from the polymerization of e-caprolactam, whereas nylon-6,6 is obtained by the condensation of hexamethylene diamine and adipic acid. 

Quite early solution blend work by Takayanagi et al. [83] of rigid aromatic polyamides (poly(p-phenylene terephthalate)) (PPTA) and flexible aliphatic polyamides, nylon 66 and nylon 6 (the latter will be discussed here) has been instrumental in developing the concept of molecular composites and although this lies more in the realm of lyotropic blends, it is often cited in the literature with regard to the effect of the PLC on the crystallization of other components in blends. PPTA has the structure... 

Figure 1.15 shows polyisobutylene, a vinylidene polymer with symmetric substitution, and thus without stereoisomers. Cis and trans isomers are possible in butenylene polymers. Two examples are at the bottom of Fig. 1.15. They are not interconvertable by rotating of the molecule. Shown in the figures are the trans isomers (). In the cis isomers the backbone chain continues on the same side of the double bond ( /). In Figs. 1.16 and 1.17 a series of vinyl and vinylidene polymers are shown. The above-mentioned PTFE, poly(vinyl butyral), and poly (methyl methacrylate) are given, starting in Fig. 1.17. Polyoxides are drawn at the bottom of Fig. 1.17, and the top of Fig. 1.18. Poly(ethylene terephthalate) and two aliphatic polyamides (nylon 6,6 and nylon 6) round out Fig. 1.18. The 20 polymers just looked at should serve as an initial list that must be extended many-fold during the course of study of thermal analysis of polymeric materials.

Figure II - 28. The chemical structure of an aliphatic polyamide (Nylon-6) and and aromatic polyamide (Nomex).

It is of interest to note that from that time nearly all the synthetic pioneering work on polymers has been carried out in industrial laboratories. This started with Carothers (Du Pont) in 1930, who studied the formation of aliphatic polyesters from diols and diacids but abandoned them in favour of aliphatic polyamides (nylons) when the polyesters were not suitable for fibres (wool and silk proteins are polyamides). It is continuing at the present time with the development of high performance aromatic polymers such as Nomex (Du Pont), Kevlar (Du Pont) and PEEK (ICI). 

Polymer chains in semicrystalline polymers such as polyolefines, aliphatic polyamides (nylons), and aliphatic polyesters crystallize in the form of lamellae of folded chains that are organized to form lamellar stacks (Fig. 2.14a). The spaces between the lamellae and between the stacks are occupied by... 

In the 1980s Keith and Padden proposed that chain tilt itself (not screw dislocations) results in axial twisting of growing lamellae that is manifested as banded spherulites. The reviews of Keith and Padden [44] and Lotz and Cheng [23] may be consulted for original references. Chain tilt is almost always found for chains crystallized in an extended (not helical) conformation. For orthorhombic polyethylene and a-poly(vinylidene fluoride), the chains are inclined to the basal lamellar surfaces to provide more volume for chain folding (Section 3.2.1). On the other hand, those aliphatic polyamides (nylons) and polyesters that crystallize with monoclinic... 

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