Nylon dyadic

The term monadic is used to describe nylons such as nylon-6 that have been produced from one reactant. The term dyadic is used to describe nylons such as nylon-6,6 that have been produced from two reactants. 

Likewise, the Tm values of aromatic polyamides (aramids) arc higher than those of the corresponding aliphatic polyamides (nylons). The Tm of monadic and dyadic nylons decreases as the number of methylene groups in the chain increases. Thus the Tm values decrease stepwise as the number of... 

Aliphatic polyamides, also known under the generic name nylon. Industrial nylons with the general structure [—RNHCO—] , such as PA-6, PA-11, and PA-12, are called monadic those with the general structure [ —NHR1NHCOR2CO —] are called dyadic (PA-4,6, PA-6,6, PA-6,9, PA-6,10, and PA-6,12). 

Likewise, the T is lower when an odd number of methylene groups are present in dyadic nylon. The of nylon 66 is 538 K, while the of nylon 56 is 496 K (Table 7.2). 

NH(CH2)5C0 4 with regular sequences of six carbon atoms between the nitrogen atoms. A nylon with two numbers is termed dyadic indicating that it contains both dibasic acid (or acid chloride) and diamine moieties, in which the first number represents the diamine and the second the diacid used in the synthesis. The monadic nylons have one number, indicating that synthesis involved only one type of monomer. This terminology means that a poly (a-amino acid) would be nylon-2. 

The best known synthetic polyamides are the nylons. The term nylon originally was a trademark for the polyamide based on hexamethylene diamine and adipic acid (Table 17.3). Later on it became a generic term. The numerals following the name designate the number of carbon atoms in the chain between successive amide groups. The dyadic nylons have two numbers the first for the diamine and the second for the diacid. Monadic nylons such as polycaprolactam require only one number. Although they have been studied as protein models, the synthetic nylon 2 polymers have not been commercialized as fibers or plastics. While some new polymers have been introduced over the years (nylon 4, nylon 1,1, nylon 1,2), nylon 6,6 and nylon 6 have been produced for a longer time and dominate the markets for synthetic polyamides, especially as fibers. 

The first step in making dyadic nylons is the formation of a salt of amine and acid (without condensation). The second step involves actual polycondensation [5]. In a batch process, salt solution is concentrated to about 75% solids before being charged along with a chain terminator such as acetic acid into an autoclave, whereas residence time of several hours and a temperature of up to 280°C yield a polymer with a molecular weight of 12 x 10 -15 x 10. A continuous process for nylon 6,6 was described in Section 5.2. 

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