Aliphatic polyamides groups

Polymide polymers contain amide group NH CO in the main chain. The most important are linear aliphatic Polyamides. These are known as nylons. Polyamides are also used as adhesives, coatings and in engineering applications. 

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... 

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. 

The three methyl groups, which account for about 11.5 and 10.5% of the weight, eliminate crystallinity completely, both for the adipic acid-based aliphatic polyamide and the terephthalic acid-based aromatic-aliphatic polyamide. 

Estimate the limiting value of Tg for polylactams (aliphatic polyamides) at increasing number of CH2 groups in the chain. 

As already mentioned, the very high chain rigidity of aliphatic polyamides and poly(alkyl isocyanate)s is due to the energy of quasiconjugation in amide groups located at a minimum distance apart along the chain. 

Aliphatic polyamides (PA) and products on their base are polymers with low stability to ultra-violet irradiation and under the effect of solar radiation they destruct less than in a year [1]. In natural conditions ultra-violet part of solar spectrum with wave-length 290-350 nm is more dangerous for these polymers, though aliphatic PAs in this field have very weak absorption of chromophore amide group [2, 3], That is why while examining the problem of PA phototransformations, unlike other polymers, both possibility of light absorption by impurities and self-absorption should be taken into consideration [4],... 

For an aliphatic polyamide that degrades by amide cleavage, the net rate of polymerization at high conversion under vacuum (that is, where the water concentration approaches zero) is given by Equation 44 where k is the rate constant for chain cleavage, and [A j] is the amide group concentration. 

The addition of lithium salts can alter the melting, flow behavior, and mechanical properties of aliphatic polyamides (1-4). These effects have been attributed to the formation of a labile network resulting from the salt interacting with the amide group of the polymer. Subsequent work using polycaprolactam lithium chloride demonstrated a direct binding of the lithium ions to the carbonyl oxygen (5). 

Figure 2.12. Blends of PA-3Me6T with aliphatic polyamides — the binary interaction parameter as a function of the -CH -Z-NHCO-group ratio for the latter polymers. Data [Elhs, 1989]. See text.

Cyclohexanone, a six-membered carbon ring with a ketone as functional group, is almost exclusively applied as a precursor for the production of aliphatic polyamides. Pure cyclohexanone is mainly converted, via cyclohexanone oxime and caprolactam, to nylon-6 (also called polycaprolactam) [1]. Mixtures of cyclohexanone and cyclohexanol, often called K4 oil, are converted via oxidation into adipic acid that reacts with hexamethylene diamine (HMDA) to nylon-6,6 (poly-hexamethylene adipamide). Other applications of these products can be found in the field of polyurethane and polyester production. 

Aliphatic polyamides are produced commercially by condensation of diamines with dibasic adds, by self-condensation of an amino acid, or by self-condensation of an amino acid, or by ring-opening polymeri2ation of a lactam [14,40,41]. To obtain polymers of high molecular weight, there should be stoichiometric equivalence of amine and acid groups of the monomers. For amino acids and lactams the stoichiometric balance is ensured by the use of pure monomers for diamines and dibasic acids this is readily obtained by the preliminary formation of a 1 1 ammonium salt, often referred to as a nylon salt. Small quantities of monofunctional compounds are often used to control the molecular weight. 

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