Carboxylic acids polyamides

As with polyesters, the amidation reaction of acid chlorides may be carried out in solution because of the enhanced reactivity of acid chlorides compared with carboxylic acids. A technique known as interfacial polymerization has been employed for the formation of polyamides and other step-growth polymers, including polyesters, polyurethanes, and polycarbonates. In this method the polymerization is carried out at the interface between two immiscible solutions, one of which contains one of the dissolved reactants, while the second monomer is dissolved in the other. Figure 5.7 shows a polyamide film forming at the interface between an aqueous solution of a diamine layered on a solution of a diacid chloride in an organic solvent. In this form interfacial polymerization is part of the standard repertoire of chemical demonstrations. It is sometimes called the nylon rope trick because of the filament of nylon produced by withdrawing the collapsed film. 

The two-step poly(amic acid) process is the most commonly practiced procedure. In this process, a dianhydride and a diamine react at ambient temperature in a dipolar aprotic solvent such as /V,/V-dimethy1 acetamide [127-19-5] (DMAc) or /V-methy1pyrro1idinone [872-50-4] (NMP) to form apoly(amic acid), which is then cycHzed into the polyimide product. The reaction of pyromeUitic dianhydride [26265-89-4] (PMDA) and 4,4 -oxydiani1ine [101-80-4] (ODA) proceeds rapidly at room temperature to form a viscous solution of poly(amic acid) (5), which is an ortho-carboxylated aromatic polyamide. 

In order to become useful dmg delivery devices, biodegradable polymers must be formable into desired shapes of appropriate size, have adequate dimensional stability and appropriate strength-loss characteristics, be completely biodegradable, and be sterilizahle (70). The polymers most often studied for biodegradable dmg delivery applications are carboxylic acid derivatives such as polyamides poly(a-hydroxy acids) such as poly(lactic acid) [26100-51-6] and poly(glycolic acid) [26124-68-5], cross-linked polyesters poly(orthoesters) poly anhydrides and poly(alkyl 2-cyanoacrylates). The relative stabiUty of hydrolytically labile linkages ia these polymers (70) is as follows ... 

Note Aldoses other than glucose can also be used e.g. arabinose [1], xylose [2, 3, 7] or ribose [4]. The background color is least on cellulose layers when cellulose acetate, aluminium oxide 150, silica gel, RP, NH2 or polyamide layers are employed the background is a more or less intense ochre. The detection limit of carboxylic acids on cellulose layers is ca. 0.5 pg substance per chromatogram zone. 

Note Silica gel, kieselguhr and polyamide layers can be used as stationary phases. Not all acids are stained on RP layers. Amino layers yield a pale blue background. The detection limits are in the pg range for carboxylic acids [1], thioglycolic and dithioglycolic acids [2] and for antithyroid pharmaceuticals [4] they are about 5 ng per chromatogram zone for sterols and steryl esters [6]. 

Polyamides and Polyesters Step-Growth Polymers 818 21.10 Spectroscopy of Carboxylic Acid Derivatives 822... 

Proteins are polyamides formed by the polymerization, through amide linkages, of a-amino acids. Three of the 25-30 important natural a-amino acids are shown in Figure 18-13. Each acid has an amine group, —NHj, attached to the a-carbon, the carbon atom immediately adjacent to the carboxylic acid group. 

Condensation polymerization of amines with carboxylic acids leads to the polyamides, substances more commonly known as nylons. A common polyamide is nylon-66, which is a polymer of 1,6-diaminohexane, H2N(GH2)6NH2, and adipic acid, HOOC(CH2)4COOH. The 66 in the name indicates the numbers of carbon atoms in the two monomers. 

Most condensation polymers are formed by the reaction of a carboxylic acid with an alcohol to form a polyester or with an amine to form a polyamide. 

Proteins are linear polyamides formed from a-amino acids. An a-amino acid is one in which carboxylic acid and the amino group reside on the same carbon atom (1.7). 

When the -OH of a carboxylic acid is replaced by an -NH2, the compound produced is an amide. Amides are neutral to mildly basic compounds. They can be made from acids, acid chlorides, acid anhydrides, and esters by reaction with ammonia or primary and secondary amines. The amide linkage is found in polyamide resins such as nylon. 

As the name implies, an amino acid is a bifunctional molecule with a carboxylic acid group at one end and an amine group at the other. All proteins are polyamides made from condensation reactions of amino acids. Every amino acid in proteins has a central carbon atom bonded to one hydrogen atom and to a second group, symbolized in Figure 13-31 as R. 

In the second part of this activity, you will prepare nylon, which is a polyamide with many amide functional groups. A common method for preparing amides is the reaction of a carboxylic-acid chloride with an amine, as in RCOCI + R NH2 - RCONHR + HCI. 

The azolide method has also been used for the synthesis of polyamides and polyimides. These can be obtained by several routes First by condensation of two dihomofunctional components (dicarboxylic acid diimidazolides and diamines), secondly by condensation of a heterodifunctional compound (amino carboxylic acid and CDI), or through reaction on a polymer (for example, polymeric carboxylic acid imidazolides and amines). 

A polyimide film was made by heating a polyamide carboxylic acid at 300 °C for 30 min with azolides such as iV-acetylimidazole, iV-trifluoroacetylimidazole, or N-benzoy limidazole.[ 1633... 

Polyamide 6 is produced by ring opening polycondensation of e- caprolactame. If no other reactants are used, the polymer chains contain one carboxylic acid and one amine end group. 

Figure 14.3 Reaction of 1,4-PBO chain extender with PET end groups (carboxylic acid groups) to give linear chain extension of PET (leading to a polyamide-polyester) 1,4-PBO, 1,4-phenylenebisoxazoline...

To the best of our knowledge, only one other example of a carboxylic acid functionalized hyperbranched structure is known in the literature, and this concerns a polyamide [19]. The synthesis reported starts from A2 (aminofunctional) and B3 (carboxylic acid functional) units and leads to low molecular weight products due to low conversion in dilute solution. These conditions were mandatory to prevent gelation [20]. Two different approaches to the synthesis of carboxylic acid functional hyperbranched polyesteramides are presented below [21]. 

Proteins are nature s polyamide condensation polymers. A protein is formed by polymerization of o-artiino acids, with the amino group on the carbon atom next to the carboxylic acid. Biologists call the bond formed a peptide rather than an amide. In the food chain these amino acids are continuously hydrolyzed and polymerized back into polymers, which the host can use in its tissues. These polymerization and depolymerization reactions in biological systems are all controlled by enzyme catalysts that produce extreme selectivity to the desired proteins. 

Metal Complexation. Azo dyes containing hydroxy or carboxylic acid gronp substituents adjacent to the azo gronp react with transition metal ions, e.g. chromium, cobalt and copper to produce complexes, e.g. Cl Acid Violet 78 (2.15)7 These metal complex dyes are more stable to light than their unmetallised precursors and have been widely nsed as dyes for polyamide and wool fibres. However, there is now a move away from chrominm complexes due to toxicity concerns (see section 2.3.2.). 

In order to develop a material with these properties, the well-documented thermal characteristics of the aromatic polyamides were combined with the sensitivity of a photolabile protecting group. In 1973, Amit and Patchornik reported that N-substituted-ortho-nitroanilides are light-sensitive and undergo a photoinduced rearrangement to produce the corresponding carboxylic acid in excellent yield. (4)... 

The reverse reaction is an intramolecular acidolysis of amide group by the (9-carboxylic acid to reform anhydride and amine. This unique feature is the result of an ortho neighboring effect. In contrast, the acylation of an amine with benzoic anhydride is an irreversible reaction under the same reaction conditions. The poly(amic acid) structure (8) can be considered as a class of polyamides. Aromatic polyamides that lack ortho carboxylic groups are very... 

As a class of compounds, nitriles have broad commercial utility that includes their use as solvents, feedstocks, pharmaceuticals, catalysts, and pesticides. The versatile reactivity of organonitriles arises both from the reactivity of the C=N bond, and from the ability of the cyano substituent to activate adjacent bonds, especially C—H bonds. Nitriles can be used to prepare amines, amides, amidines, carboxylic acids and esters, aldehydes, ketones, large-ring cyclic ketones, imines, heterocycles, orthoesters, and other compounds. Some of the more common transformations involve hydrolysis or alcoholysis to produce amides, acids and esters, and hydrogenation to produce amines, which are intermediates for the production of polyurethanes and polyamides. An extensive review on hydrogenation of nitriles has been recendy published (10). 

Carboxylic acids react with aryl isocyanates, at elevated temperatures to yield anhydrides. The anhydrides subsequently evolve carbon dioxide to yield amines at elevated temperatures (70—72). The aromatic amines are further converted into amides by reaction with excess anhydride. Ortho diacids, such as phthalic acid [88-99-3], react with aryl isocyanates to yield the corresponding N-aryl phthalimides (73). Reactions with carboxylic acids are irreversible and commercially used to prepare polyamides and polyimides, two classes of high performance polymers for high temperature applications where chemical resistance is important. Base catalysis is recommended to reduce the formation of substituted urea by-products (74). 

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