Polyamide salts

The polymerization rate is controlled by the slowest process. Thus it is important to establish the rate controlling steps. The starting material for the (SPP) can be the dry nylonsalt Z 4) but mostly a low or middle molecular weight polymer is used. The polyamide-salts have the disadvantage of high amine losses 3 4). 

Aromatic polyimides possess outstanding thermal stability as well as being unusually high melting, intractable and insoluble (1). Polyimides are prepared either by polyamide salt techniques, by condensation of dianhydrides with diisocyanates (2) or by reaction of an aromatic diamine with a dianhydride to give a poly(amic acid) followed by dehydration to give the polyimide. The polyimides from a variety of diamines have been reported and the dianhydride unit has been varied widely (1). 

Figure 2.5 Melting point of the reacting mass versus reaction time and operating temperature zone su ested for the anhydrous prepolymerization of polyamide salts [27] (reproduced with permission from Wiley).

Figure 2.13 Indicative schematic depiction from Wiley). = NHf, o = C002 of cation exchange mechanism between the —- = polyamide salt methylene groups,...

Polyamide is formed by two methods. Dual numbers arise from the first, a condensation reaction between diamines and dibasic acids produces a polyamide salt. The first number of the polyamide type refers to the number of carbon atoms in the diamine, the second number is the quantity in the acid (e.g., polyamide 612 or polyamide 66). 

The leader of DuPont s effort was Wallace H Carothers who reasoned that he could reproduce the properties of silk by constructing a polymer chain held together as is silk by amide bonds The neces sary amide bonds were formed by heating a dicar boxylic acid with a diamine Hexanedioic acid adipic acid) and 1 6 hexanediamme hexamethylenedi-amine) react to give a salt that when heated gives a polyamide called nylon 66 The amide bonds form by a condensation reaction and nylon 66 is an example of a condensation polymer... 

Amidation. Heating of the diammonium salt or reaction of the dimethyl ester with concentrated ammonium hydroxide gives adipamide [628-94-4] mp 228°C, which is relatively insoluble in cold water. Substituted amides are readily formed when amines are used. The most industrially significant reaction of adipic acid is its reaction with diamines, specifically 1,6-hexanediamine. A water-soluble polymeric salt is formed initially upon mixing solutions of the two materials then hea ting with removal of water produces the polyamide, nylon-6,6. This reaction has been studied extensively, and the hterature contains hundreds of references to it and to polyamide product properties (31). 

An alternative polymerization process utilizes a slurry of calcium chloride in NMP as the polymerization medium. The solubiHty of calcium chloride is only 6% at 20°C however, the salt continues to dissolve as conversion of monomers to polymer proceeds and calcium chloride/polyamide complexes are formed. Polymer molecular weight is further increased by the addition of /V, /V- dim ethyl a n i1 in e as an acid acceptor. This solvent system produces fiber-forming polymer of molecular weights comparable to that formed in HMPA/NMP. 

Direct amidation is generally carried out ia the melt, although it can be done ia an iaert solvent starting from the dry salt (46). Because most aUphatic polyamides melt ia the range of 200—300°C and aromatic-containing polyamides at even higher temperatures, the reactants and products must be thermally stable to be polymerized via this method. 

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. 

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. 

Acid—mordant dyes have characteristics similar to those of acid dyes which have a relatively low molecular weight, anionic substituents, and an affinity to polyamide fibers and mordant dyes. In general, brilliant shades caimot be obtained by acid—mordant dyes because they are used as their chromium mordant by treatment with dichromate in the course of the dyeing procedure. However, because of their excellent fastness for light and wet treatment, they are predominandy used to dye wool in heavy shades (navy blue, brown, and black). In terms of chemical constitution, most of the acid—mordant dyes are azo dyes some are triphenyhnethane dyes and very few anthraquinone dyes are used in this area. Cl Mordant Black 13 [1324-21 -6] (183) (Cl 63615) is one of the few examples of currentiy produced anthraquinone acid—mordant dyes. It is prepared by condensation of purpurin with aniline in the presence of boric acid, followed by sulfonation and finally by conversion to the sodium salt (146,147). 

Direct Dyes. These are defined as anionic dyes, again containing sulfonic acid groups, with substantivity for ceUulosic fibers. They are usually a2o dyes (qv) and can be mono-, dis-, or polya2o, and are ia general planar stmctures. They are appHed to ceUulosic fibers from neutral dyebaths, ie, they have direct substantivity without the need of other agents. Salt is used to enhance dyebath exhaustion. Some direct dyes can be appHed to wool and polyamides under acidic conditions, but these are the exception. 

The preparation of nylon resins from lactam precursors involves ring opening, which is facihtated by a controlled amount of water in the reaction mixture. The salt complex condenses internally to produce the polyamide (57). The synthesis of nylon-6 [25038-54-4] from S-caprolactam is as follows ... 

Acid chlorides are very reactive and have as a condensation product hydrochloric acid.4,7 9 This hydrochloric acid can form an amine salt with unreacted amine groups, which should be avoided. To prevent this happening, acid binders, which are more reactive than the amines, are added. Polyamidation can be earned out using a solution and with an interfacial method. With the interfacial method one has the choice between a stirred and an unstirred process. In an unstirred process, the polymerization is at the interface and a rope can be drawn from the interface,... 

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. 

Acid anhydride-diol reaction, 65 Acid anhydride-epoxy reaction, 85 Acid binders, 155, 157 Acid catalysis, of PET, 548-549 Acid-catalyzed hydrolysis of nylon-6, 567-568 of nylon-6,6, 568 Acid chloride, poly(p-benzamide) synthesis from, 188-189 Acid chloride-alcohol reaction, 75-77 Acid chloride-alkali metal diphenol salt interfacial reactions, 77 Acid chloride polymerization, of polyamides, 155-157 Acid chloride-terminated polyesters, reaction with hydroxy-terminated polyethers, 89 Acid-etch tests, 245 Acid number, 94 Acidolysis, 74 of nylon-6,6, 568... 

American Society for Testing and Materials (ASTM), 242 Amic acid ammonium salt, polyimide cyclization via, 305 Amic acid formation, 301 Amidation reaction scheme, 151 Amide-amide interchange reaction, 158 Amide concentration, in polyamides, 139-141... 

For condensation polymerization, it is necessary to have two functional groups on each monomer and to mix stoichiometric amounts of the reactants. In polyamide production, the starting materials first form nylon salt by proton transfer ... 

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. 

Polycondensation pol5mers, like polyesters or polyamides, are obtained by condensation reactions of monomers, which entail elimination of small molecules (e.g. water or a hydrogen halide), usually under acid/ base catalysis conditions. Polyolefins and polyacrylates are typical polyaddition products, which can be obtained by radical, ionic and transition metal catalyzed polymerization. The process usually requires an initiator (a radical precursor, a salt, electromagnetic radiation) or a catalyst (a transition metal). Cross-linked polyaddition pol5mers have been almost exclusively used so far as catalytic supports, in academic research, with few exceptions (for examples of metal catalysts on polyamides see Ref. [95-98]). 

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