Nylons high-molecular-weight polyamides

Carothers next step was to move from polyesters to nylons and to increase the fractional conversion (p) by making salts using the equivalent reaction of 1,6-hexanediamine (hexamethylenediamine) and adipic acid. These salts were recrystallizable from ethanol giving essentially a true 1 1 ratio of reactants. Thus, a high molecular weight polyamide, generally known as simply a nylon, in this case nylon-6,6, was produced from the thermal decomposition of this equimolar salt as shown in structure 4.55. This product has a melting point of 265°C. 

Joyce and Ritter (1) in 1941 obtained a patent on the base catalyzed polymerization of caprolactam. They described the reaction of a small amount of sodium or other alkali metal in caprolactam to form sodium caprolactam and the rapid, exothermic polymerization of caprolactam above 200°C to form molten nylon polymer. The polymerization reaction is an isomerization of the low viscosity cyclic amide to a high viscosity, high molecular weight polyamide. 

Polyamides. Although high molecular weight polyamides such as nylon-6, nylon-6,6, and nylon-12 resisted microbial (3, 4,19) and enzyme attack (17), low molecular weight cyclic and linear oligomers of c-aminocaproic acid were utilized by certain bacteria isolated from the effluent water of a nylon-6 plant. These include Corynebacterium auran-tiacum B-2 reported by Fukumura (20,21) and Achromobacter guttatus KI 72 reported by Okada et al. (22). 

Nylon. Nylon is a trade name for high-molecular weight polyamides that result from condensation polymerization of dibasic acids and diamines, or from u)-amino acids. Nylon can be extruded from a melt as monofilaments, or spun from a solution of formic acid, HCOOH, and phenol, C5H5OH. The resulting fibers have a low density, are elastic and lustrous, and mass for mass are stronger than steel. However, they are also low melting and difficult to dye. 

Certain specialty nylon resins with low melting temperatures have been used quite successfully with extrusion techniques. Both nylon and high-molecular-weight polyamide resins that are chemically related to dimer acid-based polyamides are used in high-strength metal-to-metal adhesives they are applied by extrusion. ... 

High molecular weight polyamides are commonly known as nylon. Polyamides are crystalline polymers typically produced hy the condensation of a diacid and a diamine. There are several types and each type is often descrihed hy a number, such as Nylon 66 or Polyamide 66 (PA66). The numeric suffixes refer to the number of carbon atoms present in the molecular structures of the amine and acid respectively (or a single suffix if the amine and acid groups are part of the same molecule). 

A mixture of a diacid and a diamine was the starting material for the first commercial, high molecular weight, polyamide. Hexamethylene diamine or HMDA (1,6 diaminohexane) and adipic acid (1,6 hexanedloic acid) yield nylon 66, so named because each monomer contains six carbon... 

The history of all nylon development begins with the discovery in 1935 of the first high molecular weight polyamide, Nylon 66. 

Finally, when polyamides containing four or five carbon diacids, ie, succinic acid [110-15-6] and glutaric acid [110-94-1], respectively, are heated, they form cychc imides that cap the amine ends and prevent high molecular weights from being achieved (84). For nylon-x,4, n = 1 and for nylon-x,5, n = 2. 

Nylon 66. The word nylon was established as a generic name for polyamides, one class of the new high molecular weight linear polymers. The first of these, and the one still produced in the largest volume, was nylon 66 or polyhexamethylene adipamide. Numbers are used following the word nylon to indicate the number of carbon atoms contributed by the diamine and dicarboxylic acid constituents, in this case hexamethylenediamine and adipic acid, respectively. 

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. 

The word reinforcement will refer in this book exclusively to strong, stiff fibres. They can be made of glass, aramid (e.g. KevlaT (DuPont)) or high molecular weight polyethylene (e.g. Dyneema (DSM)), carbon/graphite, polyamide (nylon), jute, and so on. The fibres can be long, virtually continuous or short (e.g. 1mm). 

Nylon 6,6 is a condensation product of hexamethylenediamine and adipic acid. This polyamide was originally synthesized in 1935 and first produced conunercially in 1938. It is still one of the major commercial nylons produced today. Because high molecular weight is required for such polymers to possess good physical properties, it is necessary to follow exact stoichiometry of the reactants in the condensation. To achieve that, the practice is to initially form a nylon salt prior to the polymerization. To do this, equimolar quantities of adipic acid and hexamethylenediamine are combined in aqueous environment to form solutions of the salt. The end point is controlled electrochemically. An alternate procedure is to combine the diacid with the diamine in boiling methanol. A1 1 adduct precipitates out, is filtered off, and dissolved in water. 

Once two monomers (with opposing functionality) interact, the average value for Mo equals half of the mass of the repeat unit. Equation (2-63) points out how difficult it will be to reach high molecular weight materials via condensation reactions. Looking, for example, at the formation of polyamide Nylon 6-6. 

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