High molecular weight nylon-polymer

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. 

Boontongkong Y, Cohen R E, Spector M and Bellare A (1998) Orientation of plane strain-compressed ultra-high-molecular-weight polyethylene. Polymer 39 6391-6400. Lin L, Argon A S (1992) Deformation resistance in oriented nylon 6, Macromolectdes 25 4011-4024. 

This rather simple conclusion was reached by W.H. Carothers, the discoverer of nylon and one of the founders of polymer science, in the 1930s. (The same result may be obtained in a more laborious fashion by inserting Equation 8.3 into Equation 5.24.) Its importance becomes obvious when it is realized that typical linear polymers must have values on the order of at least 100 to achieve useful mechanical properties. This requires a conversion of at least 99%, assuming difunctional monomers in perfect stoichiometric equivalence. Such high conversions are almost unheard in most organic reactions, but are necessary to achieve high molecular weight condensation polymers. 

This compound is sometimes called a nylon salt. The salt polymer equilibrium is more favorable to the production of polymer than in the case of polyesters, so this reaction is often carried out in a sealed tube or autoclave at about 200°C until a fairly high extent of reaction is reached then the temperature is raised and the water driven off to attain the high molecular weight polymer. 

Caprolactam is an amide and, therefore, undergoes the reactions of this class of compounds. It can be hydrolyzed, Ai-alkylated, O-alkylated, nitrosated, halogenated, and subjected to many other reactions (3). Caprolactam is readily converted to high molecular weight, linear nylon-6 polymers. Through a complex series of reactions, caprolactam can be converted to the biologically and nutritionally essential amino acid L-lysine (10) (see Amino acids). 

The diamine and diacid monomers used to make type AABB nylons are typically rather difficult to handle in their pure form. Diamines are liquids or semisolids at room temperature, while the diacids are crystalline solids. These monomers become much more manageable when they are combined to form nylon salts, as shown in Fig. 23.7 a). Nylon salts are solids that can be easily handled and ensure a stoichiometric balance between the diacid and diamine, which is necessary to produce high molecular weight polymers. In the case of nylon 66, the precursor salt is made by boiling adipic acid and hexamethylene diamine in methanol, from which the nylon salt precipitates. 

For the first method exact equivalence of reactants are used to obtain high Molecular weight polymer. In the first step an aqueous solution of adipic acid is neutralised with hexamethylene diamine to form nylon salt. 

Nylon 12 is prepared by heating dodecyl lactam at 300°C in presence of phoshoric acid to obtain a high Molecular weight polymer. 

Polymers are large, high molecular weight compounds formed by linking together many smaller compounds called monomers. The properties of the polymer are dependent on the monomer units used and the way in which they link together. Many polymers occur in nature such as cellulose, starch, cotton, wool, and rubber. Others are created synthetically, such as nylon, PVC, polystyrene, Teflon, and polyester. 

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