Aliphatic polyamides polyamide 66, structure

There are a number of structural variables which can considerably affect the properties of the aliphatic polyamides ... 

Aliphatic hyperbranched polyesters, 56 Aliphatic isocyanate adducts, 202 Aliphatic isocyanates, 210, 225 Aliphatic polyamides, 138 Aliphatic polyesteramides, 56 Aliphatic polyesters, 18, 20, 29, 32, 87 degradable, 85 hyperbranched, 114-116 melting points of, 33, 36 structure and properties of, 40-44 syntheses of, 95-101 thermal degradation of, 38 unsubstituted and methyl-substituted, 36-38... 

Polyamides are macromolecules with acidamide units —CONH—, where the chemical structure of the other parts of the monomers can be aliphatic and/or aromatic. Similar structures are found in nature, for example, polypeptides. Although in principle a large number of potential polyamide structures can be produced, only a few polyamides are produced in industrial scale. 

The dipole associated with the maleimide unit, which is located in the plane of the maleimide cycle and perpendicular to the C - C bond taking part to the chain backbone. The motion of this resultant dipole implies a rotation of the rigid maleimide unit around the local chain axis. This structure is, in some way, analogous to that encountered with iso-phthalic units in aryl-aliphatic polyamides (Sect. 6) where the zso-phthalic rings only undergo small amplitude oscillations but no flips at temperatures below the glass transition temperature. Thus, it is unlikely that the maleimide dipole could be involved in the transition motions of CMIMx copolymers. 

The curves shown in Fig. 81 are quite similar to those observed in the case of fracture of aryl-aliphatic polyamides (Sect. 5.3). However, in the latter system, a large range of MWs and chemical structures are available, allowing a detailed analysis of the observed behaviours. For these reasons, the analysis of fracture results for BPA-PC takes advantage of those on aryl-aliphatic polyamides. 

Nonetheless a few commercially successful noncellulosic membrane materials were developed. Polyamide membranes in particular were developed by several groups. Aliphatic polyamides have low rejections and modest fluxes, but aromatic polyamide membranes were successfully developed by Toray [25], Chemstrad (Monsanto) [26] and Permasep (Du Pont) [27], all in hollow fiber form. These membranes have good seawater salt rejections of up to 99.5 %, but the fluxes are low, in the 1 to 3 gal/ft2 day range. The Permasep membrane, in hollow fine fiber form to overcome the low water permeability problems, was produced under the names B-10 and B-15 for seawater desalination plants until the year 2000. The structure of the Permasep B-15 polymer is shown in Figure 5.7. Polyamide membranes, like interfacial composite membranes, are susceptible to degradation by chlorine because of their amide bonds. 

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

Aliphatic polyamides, also known under the generic name nylon. Industrial nylons with the general structure [—RNHCO—] , such as PA-6, PA-11, and PA-12, are called monadic those with the general structure [ —NHR1NHCOR2CO —] are called dyadic (PA-4,6, PA-6,6, PA-6,9, PA-6,10, and PA-6,12). 

It was of interest to examine the permeation properties of this class of aliphatic-aromatic polyamides. More specifically, it was desired to determine the effect of changes in chemical structure upon OPV and upon the RH dependence of OPV. It was also desired to determine the factors which lead to these observed structural effects. 

Aliphatic polyamides are extensively studied by natural abundance 15NNMR spectroscopy in solution. However, characterization of polyamides in solution is limited by the insolubility of many (particularly aromatic) polyamides. On the other hand, chemical shifts of amide nitrogens are strongly dependent on the nature of a solvent, and for a particular polyamide, could cover approximately 20 ppm, as in the case of fluorosulfonic acid and trifluoroethanol (see Fig. 2). Since the important properties of solid polyamides such as crystalline structure and hydrogen bonding cannot be studied by solution spectra, the various solid state 15N NMR techniques have been used for structural and dynamical characterization of these polymeric materials. 

Polyamides can be prepared with aliphatic or aromatic monomers, either acids or amines. Aliphatic polyamides are usually hygroscopic materials, and the introduction of the aromatic ring in the monomer structure can reduce this characteristic. Water in polyamides is an important impurity when they are processed through injection molding. 

Aliphatic or aromatic structure, as weU as liner or branched structure of the reactants, can give the microcapsule shell different porosity and permeability, which can greatly inflnence the release performances. Multifunctional reactants can help to achieve more thermal mechanical stable microcapsules since the wall is a three-dimensional cross-linked polymer network. Experiments have shown that dichlorides with less than eight carbon atoms do not prodnce qnahty polyamide microcapsules. The reason behind this is the competition between interfacial condensation and the hydrolysis reaction of dichlorides. More hydrophobic dichlorides can favor the polymerization and slow the hydrolysis. Similarly, for polyurethane and polyurea type microcapsules, polymeric isocy-nates are preferred because they might favor the formation of less permeable miCTocapsnles for the hydrolysis of isocynate groups are limited, which consequently reduced the COj release that contribute to the porosity increase of the polymer wall." ... 

Aliphatic polyamides are macromolecules whose structural units are characteristically interlinked by the amide linkage —NHCO—. The nature of the structural unit constitutes a basis for classification. Aliphatic polyamides with structural units derived predominantly from aliphatic monomers are members of the generic class of nylons, whereas aromatic polyamides in which at least 85% of the amide linkages are directly adjacent to aromatic structures have been designated aramids. This chapter is concerned with nylons, especially those of commercial importance. Aramids are discussed in a separate chapter. 

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