Step 6 polyamide

The second difficulty, degradation, required the development of a two-step polyamidation process following salt formation (157). During salt formation, tetramethylenediammonium adipate salt is formed in water solution at approximately 50% concentration or at a higher concentration in a suspension. As in nylon-6,6 manufacture, this salt solution, when diluted, permits easy adjustment of the stoichiometry of the reactants by means of pH measurement. 

Polyamides are intrinsically hygroscopic because of the polar nature of their chains, which makes them moisture-sensitive materials, and hence chemically unstable towards hydrolytic conditions. Prior to processing steps, polyamide composites need to be dried in order... 

Polyesters and polyamides are two of the most studied step-growth polymers, as well as being substances of great commercial importance. We shall consider polyesters in the next section, and polyamides in Sec. 5.6. 

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. 

Quality Specifications. Because of the extreme sensitivity of polyamide synthesis to impurities ia the iagredients (eg, for molecular-weight control, dye receptivity), adipic acid is one of the purest materials produced on a large scale. In addition to food-additive and polyamide specifications, other special requirements arise from the variety of other appHcations. Table 8 summarizes the more important specifications. Typical impurities iaclude monobasic acids arising from the air oxidation step ia synthesis, and lower dibasic acids and nitrogenous materials from the nitric acid oxidation step. Trace metals, water, color, and oils round out the usual specification Hsts. 

Lewis acids, such as the haUde salts of the alkaline-earth metals, Cu(I), Cu(II), 2inc, Fe(III), aluminum, etc, are effective catalysts for this reaction (63). The ammonolysis of polyamides obtained from post-consumer waste has been used to cleave the polymer chain as the first step in a recycle process in which mixtures of nylon-6,6 and nylon-6 can be reconverted to diamine (64). The advantage of this approach Hes in the fact that both the adipamide [628-94-4] and 6-aminohexanoamide can be converted to hexarnethylenediarnine via their respective nitriles in a conventional two-step process in the presence of the diamine formed in the original ammonolysis reaction, thus avoiding a difficult and cosdy separation process. In addition, the mixture of nylon-6,6 and nylon-6 appears to react faster than does either polyamide alone. 

In the final step the dinitrile is formed from the anti-Markovrukov addition of hydrogen cyanide [74-90-8] at atmospheric pressure and 30—150°C in the hquid phase with a Ni(0) catalyst. The principal by-product, 2-methylglutaronitrile/4j5 j5 4-ti2-, when hydrogenated using a process similar to that for the conversion of ADN to hexamethylenediamine, produces 2-meth5i-l,5-pentanediamine or 2-methylpentamethylenediamine [15520-10-2] (MPMD), which is also used in the manufacture of polyamides as a comonomer. 

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. 

The maleimide is prebuilt into the molecule in a separate step. Maleimidobenzoic acid [17075-07-7] or its acid haUde was used to synthesize maleintide-terrninated polyamides (16,17) or polyesters (27) from amino- or hydroxy-terminated polyamides and polyesters, respectively. The Hterature on bismaleimide prepolymers and bismaleimide building blocks is quite extensive (28), but only a limited number of BMI building blocks have been used for commercial resin formulations. 

Polyamides (nylons) are thermoplastic fibers that retain their form produced by heat treatment. They are usually given an alkaline scour and then heat-set. The heat-setting treatment is conducted at ca 10°C above the subsequent wet processiag steps this ensures good form retention after processiag. Woven fabrics are usually heat-set on a contact heat-setting machine and nylon tricot is generally heat-set on a tenter frame or ia steam chambers. 

Seb cic Acid. Sebacic acid [111-20-6] C QH gO, is an important intermediate in the manufacture of polyamide resins (see Polyamides). It has an estimated demand worldwide of approximately 20,000 t/yr. The alkaline hydrolysis of castor oil (qv), which historically has shown some wide fluctuations in price, is the conventional method of preparation. Because of these price fluctuations, there have been years of considerable interest in an electrochemical route to sebacic acid based on adipic acid [124-04-9] (qv) as the starting material. The electrochemical step involves the Kolbn-type or Brown-Walker reaction where anodic coupling of the monomethyl ester of adipic acid forms dimethyl sebacate [106-79-6]. The three steps in the reaction sequence from adipic acid to sebacic acid are as follows ... 

Major fiber-making polymers are those of polyesters, polyamides (nylons), polyacrylics, and polyolefins. Polyesters and polyamides are produced by step polymerization reactions, while polyacrylics and polyolefins are synthesized by chain-addition polymerization. 

The alkene and diene polymers discussed in Sections 7.10 and 14.6 are called chain-growth polymers because they are produced by chain reactions. An initiator adds to a C=C bond to give a reactive intermediate, which adds to a second alkene molecule to produce a new1 intermediate, which adds to a third molecule, and so on. By contrast, polyamides and polyesters are called step-growth polymers because each bond in the polymer is formed independently of the others. A large number of different step-growth polymers have been made some of the more important ones are shown in Table 21.2. 

The best known step-growth polymers are the polyamides, or nylons, first prepared by Wallace Carothers at the DuPont Company by heating a diamine with a diacid. Por example, nylon 66 is prepared by reaction of adipic acid (hexanedioic acid) with hexamethylenediamine (.1.,6-hexanediamine) at 280 °C. The designation "66" tells the number of carbon atoms in the diamine (the first 6) and the diacid (the second 6). 

Step-growth polymers, such as polyamides and polyesters, are prepared by reactions between difunctional molecules. Polyamides (nylons) are formed by reaction between a diacid and a diamine polyesters are formed from a diacid and a diol. 

Step-growth polymers are produced by reactions in which each bond in the polymer is formed stepwise, independently of the others. Like the polyamides (nylons) and polyesters that we saw in Section 21.9, most step-growth polymers... 

Nylon (Section 21.9) A synthetic polyamide step-growth polymer. 

Step-growth polymer (Sections 21.9, 31.4) A polymer in which each bond is formed independently of the others. Polyesters and polyamides (nylons) are examples. 

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

Membranes used for the pressure driven separation processes, microfiltration (MF), ultrafiltration (UF) and reverse osmosis (RO), as well as those used for dialysis, are most commonly made of polymeric materials. Initially most such membranes were cellulosic in nature. These ate now being replaced by polyamide, polysulphone, polycarbonate and several other advanced polymers. These synthetic polymers have improved chemical stability and better resistance to microbial degradation. Membranes have most commonly been produced by a form of phase inversion known as immersion precipitation.11 This process has four main steps ... 

Even within a particular class of polymers made by step-growth polymerization, monomer composition can be varied to produce a wide range of polymer properties. For example, polyesters and polyamides can be low-Tg, amorphous materials or high-Tg, liquid crystalline materials depending on the monomer composition. 

Nearly all of the polymers produced by step-growth polymerization contain heteroatoms and/or aromatic rings in the backbone. One exception is polymers produced from acyclic diene metathesis (ADMET) polymerization.22 Hydrocarbon polymers with carbon-carbon double bonds are readily produced using ADMET polymerization techniques. Polyesters, polycarbonates, polyamides, and polyurethanes can be produced from aliphatic monomers with appropriate functional groups (Fig. 1.1). In these aliphatic polymers, the concentration of the linking groups (ester, carbonate, amide, or urethane) in the backbone greatly influences the physical properties. 

Linear step-growth polymerizations require exceptionally pure monomers in order to ensure 1 1 stoichiometry for mutually reactive functional groups. For example, the synthesis of high-molecular-weight polyamides requires a 1 1 molar ratio of a dicarboxylic acid and a diamine. In many commercial processes, the polymerization process is designed to ensure perfect functional group stoichiometry. For example, commercial polyesterification processes often utilize dimethyl terephthalate (DMT) in the presence of excess ethylene glycol (EG) to form the stoichiometric precursor bis(hydroxyethyl)terephthalate (BHET) in situ. 

The AA-BB polyamides are nearly always prepared using bulk polymerization with a prepolymerization step at higher pressure, although not every laboratory has die facility to carry out a polymerization in an autoclave. Nielinger50 has reported bulk polymerization of PA-6,1 from its salt solution at atmospheric pressure (Example 11). This mediod may also be usable for other laboratory polymerizations like PA-6,6. 

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