Polyamides from Diamines and Dicarboxylic Acids

The polycondensation of diamines with dicarboxylic acids can be carried out simply by melting together the highly purified components under nitrogen at 180-300°C. However, considerable amounts of diamine can be carried over with the water that distills off, especially towards the end of the reaction when vacuum is applied. The equivalence of the reaction partners, which is a prerequisite for the attainment of a high molecular weight, is thereby disturbed. Therefore, it is 

An elegant variation of this procedure is to carry out the polycondensation with the salt of a diamine and a dicarboxylic acid (see Example 4.10). In this case, the formation of salt (which is also the first step in the direct polycondensation of a diamine and a dicarboxylic acid) and the polycondensation are carried out as two separate steps. The salts can be obtained in good crystalline form most simply by mixing equimolar amounts of diamine and dicarboxylic acid in a solvent in which the salt formed is insoluble (e.g., ethanol). In order to attain high molecular weights by such polycondensations the salts should be as neutral as possible (exactly equivalent amounts of diamine and dicarboxylic acid) and very pure (recrystaUize, for example, from mixtures of ethanol/water). 

Example 4.10 Preparation of Polyamide-6,6 from Hexamethylenediammonium Adipate (AH Salt) by Condensation in the Melt 

Safety precautions Before this experiment is carried out. Sect. 2.2.5 must be read as well as the material safety data sheets (MSDS) for all chemicals and products used. 

12 g (0.082 mol) of pure adipic acid (mp 152°C) are dissolved in 100 ml of 95% ethanol and 9.7 g (0.082 mol) of pure hexamethylenediamine are dissolved in a mixture of 27 ml of ethanol and 10 ml of water. Both solutirms are filtered if they are not perfectly clear. 

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An example of a condensation polymerization is given by the formation of polyamides from diamines and dicarboxylic acids with elimination of water ... 

Polyamides from Diamines and Dicarboxylic Acid Derivatives... 

The manufacture of the large variety of polyamides (commonly referred to as nylons) occurs through polycondensation of amino carboxylic acids (or functional derivatives of them, e.g. lactams) and from diamines and dicarboxylic acids. Labeling the amino groups with A and the carboxyl groups with B allows differentiation of the different chemical structures between the two types AB (from amino carboxylic acids) and AA-BB (from diamines and dicarboxylic acids). The number of C atoms in the monomers acts as a code number for the identification of the polyamides. The polycaprolactam manufactured from caprolactam (type AB) is then called polyamide 6 (PA 6). The number of carbon atoms in the diamine is given first for type AA-BB followed by the number of atoms in the dicarboxylic acid, e.g. PA 66 for polyhexamethylenedia-dipic amide from hexamethylenediamine and adipic acid. For copolymers the components are separated by a slash, e.g. PA 66/6 (90 10) is a copolymer composed of 90 parts PA 66 and 10 parts PA 6. 

In the early days of macromolecular chemistry, synthetic polymers were simply labeled according to the monomer from which they were prepared. Thus, ethylene polymers became poly(ethylenes), styrene polymers became poly(styrenes), and those from lactams became poly (lactams). In other cases, the choice of name was provided by a characteristic group occurring in the final polymer. Thus, polymers from diamines and dicarboxylic acids were called polyamides, and those from diols and dicarboxylic acids were called polyesters. This phenomenological nomenclature fails, of necessity, when more than one kind of monomeric unit can be formed from a given monomer. 

Polymers with n = 6, polyamide-6 (or poly(caprolactam)), with n = 11, polyamide-11 and = 12, polyamide-12 (or poly(lauryl lactam)) are commercially important. The second type of polyamide is produced from diamines and dicarboxylic acids. These have the structural unit ... 

Fully aromatic polyamides are synthesized by interfacial polycondensation of diamines and dicarboxylic acid dichlorides or by solution condensation at low temperature. For the synthesis of poly(p-benzamide)s the low-temperature polycondensation of 4-aminobenzoyl chloride hydrochloride is applicable in a mixture of N-methylpyrrolidone and calcium chloride as solvent. The rate of the reaction and molecular weight are influenced by many factors, like the purity of monomers and solvents, the mode of monomer addition, temperature, stirring velocity, and chain terminators. Also, the type and amount of the neutralization agents which react with the hydrochloric acid from the condensation reaction, play an important role. Suitable are, e.g., calcium hydroxide or calcium oxide. 

The fiftieth anniversary of the announcement of nylon as the first synthetic organic textile fiber by the Du Pont Co. on October 27,1938 was celebrated as a significant event by the textile industry in 1988 (1,2). The announcement was the culmination of the fundamental research efforts of W. H. Carothers and his team at Du Pont (3). Carothers synthesized diamines from C2 to C18 in order for them to react with a variety of aliphatic dicarboxylic acids to make polyamides for evaluation as fibers (4—10). Alicyclic and aromatic diamines and dicarboxylic acids were also included. Nylon-6,6 was ultimately selected for scale-up and development because of its favorable melting point ( 260° C), best balance of properties, and lower manufacturing cost. The pilot plant for nylon-6,6 was completed in Wilmington, Delaware, in July, 1938, and a product was introduced on the market as Exton brisdes for Dr. West s toothbrushes (2). The first nylon filament plant was built in 1939 at Seaford, Delaware, and nylon stockings went on sale on October 24,1939 only to residents of Wilmington, and then nationally, on May 15, 1940 (2). 

Some of the most familiar reactions falling into the polycondensation class are those leading to polyamides derived from dicarboxylic acids and diamines, polyesters from glycols and dicarboxylic acids, polyurethanes from polyols and polyisocyanates, and polyureas from diamines and diisocyanates. Similar polymer formations utilizing bifunctional acid chlorides with polyols or polyamines also fall into this class. The condensations of aldehydes or ketones with a variety of active hydrogen compounds such as phenols and diamines are in this group. Some of the less familar polycondensation reactions include the formation of polyethers from bifunctional halogen compounds and the sodium salts of bis-phenols, and the addition of bis-thiols to diolefins under certain conditions. 

The polyamides (nylons) were given a special naming system. Nylons made from diamines and dicarboxyfic acids are designated by two numbers, the first representing the number of carbons in the diamine chain (a) and the second the number of carbons in the dicarboxylic acid (h). (See Figure 3.)... 

There are a number of other specialty polyamides produced from a combination of other diamines and dicarboxylic acids and/or lactams of varying number of carbon atoms. PA-11 and PA-12 with 11 and 12 methylene units between each repeat amide group are relatively low melting point (170°C), but exhibit excellent ductility and moisture resistance. 

More recently, the synthesis of partially aromatic polyamides from linear nonaromatic dicarboxylic acids (i.e., adipic, suberic, sebacic, and fumaric acid) and aromatic diamines such as p-phenylenediamine or 2,5-bis(4-aminophenyl)-3,4-diphenylthiophene (Fig. 12) under microwave conditions was presented by Pour-javadi et al. [74]. 

Nylon Resins n Polyamide resins made from the interaction of diamines and dicarboxylic acids. Hexamethylene diamine and adipic acid are typical reactants. These resins are composed principally of a long-chain synthetic polymeric amide which has recurring amide groups as an integral part of the main polymer chain. 

Figure 2.24 Synthesis of polyamide from erythritol-derived diamine and dicarboxylic acid dichloride.

Figure 32 Synthesis of aliphatic polyamides from co-amino acids as well as diamines and dicarboxylic acids.

Figure 33 Synthesis of polyamides from linear nonaromatic dicarboxylic acids (i.e., adipic, suberic, sebacic, and fumaric acid) and aromatic diamines.

Nylon A class of synthetic fibres and plastics, polyamides. Manufactured by condensation polymerization of ct, oj-aminomonocarboxylic acids or of aliphatic diamines with aliphatic dicarboxylic acids. Also rormed specifically, e.g. from caprolactam. The different Nylons are identified by reference to the carbon numbers of the diacid and diamine (e.g. Nylon 66 is from hexamethylene diamine and adipic acid). Thermoplastic materials with high m.p., insolubility, toughness, impact resistance, low friction. Used in monofilaments, textiles, cables, insulation and in packing materials. U.S. production 1983 11 megatonnes. 

It has become the custom to name linear aliphatic polyamides according to the number of carbon atoms of the diamine component (first named) and of the dicarboxylic acid. Thus, the condensation polymer from hexamethylenedi-amine and adipic acid is called polyamide-6,6 (or Nylon-6,6), while the corresponding polymer from hexamethylenediamine and sebacoic acid is called polyamide-6,10 (Nylon-6,10). Polyamides resulting from the polycondensation of an aminocarboxylic acid or from ring-opening polymerization of lactams are indicated by a single number thus polyamide-6 (Nylon-6) is the polymer from c-aminocaproic acid or from e-caprolactam. 

A variety of polyamides can be made by heating diamines with dicarboxylic acids. The most generally useful of these is nylon 66, the designation 66 arising from the fact that it is made from the. vA-carbon diamine, 1,6-hexanediamine, and a six-carbon diacid, hexanedioic acid ... 

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. 

In a similar way, the synthesis of aromatic polyamides from aromatic diamines m-phenylenediamine, p-phenylenediamine, bis(4-aminophenyl)methane, and bis(4-aminophenyl)ether and dicarboxylic acids such as isophthalic and tereph-thalic acid was performed in a household microwave oven [72]. The polycondensation was carried out in an JV-methyl-2-pyrrolidone (NMP) solution in the presence of triphenyl phosphite (TPP), pyridine, and lithium chloride as condensing agents to produce a series of polyamides with moderate inherent viscosities of 0.21-0.92 dL/g within 30-50 s. However, no marked differences in molecular weight distribution and inherent viscosities between the polyamides produced by conventional (60 s, 220 °C) and microwave methods were found [72]. 

Syntheses of aliphatic polyesters and polyamides by 02 + 2 polycondensations in the melt were first studied by Carothers in the years 1930-1937 (see Chap. 3). Since that time Nylon-6,6 type aliphatic polyamides were and are prepared from equimolar monomer mixtures usually supplied in the form of diamine-dicarboxylic acid salts. In the case of aliphatic polyesters two different procedures are applicable, depending on the volatility of the reaction partners. Combinations of low boiling esters such as dimethyl succinate and low boiling dieols (e.g., ethanediol) are best polymerized in equimolar feed ratios Equimolar feed ratios are again advisable for combinations of long a,m-alkanediols and dicarboxylic acids or their... 

Diselosed is a proeess for the simultaneous production of dicarboxylic acids and diamines from a) polymers based on polyamides of dicarboxylic acids or their derivatives with diamines or b) compositions containing essentially such polymers. It involves treating these polymers or compounds with a base in alcoholic medium and subsequently converting the resulting dicarboxylate salts electrochemically into the corresponding dicarboxylic acids and bases. 

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