Editing Polyamide

{{Short description|Macromolecule with repeating units linked by amide bonds}}
A '''polyamide''' is a [[polymer]] with [[repeating unit]]s linked by [[amide]] bonds.<ref>Palmer, R. J. 2001. Polyamides, Plastics. Encyclopedia Of Polymer Science and Technology. {{doi|10.1002/0471440264.pst251}}</ref>

Polyamides occur both naturally and artificially. Examples of naturally occurring polyamides are [[protein]]s, such as [[wool]] and [[silk]]. Artificially made polyamides can be made through [[step-growth polymerization]] or [[solid-phase synthesis]] yielding materials such as [[nylon]]s, [[aramid]]s, and [[sodium polyaspartate]]. Synthetic polyamides are commonly used in textiles, automotive industry, carpets, kitchen utensils and sportswear due to their high durability and strength. The transportation manufacturing industry is the major consumer, accounting for 35% of polyamide (PA) consumption.<ref>[http://www.ceresana.com/en/market-studies/plastics/engineering-plastics/ Market Study Engineering Plastics, Ceresana, Sep 2013]</ref>

==Classification==
Polymers of [[Amino acid|amino acids]] are known as [[polypeptides]] or [[proteins]].

According to the composition of their main chain, synthetic polyamides are classified as follows:

{| class="wikitable"
|-
! Family !! Main chain !! Examples !! Commercial products
|-
| [[Aliphatic compound|Aliphatic]] polyamides || Aliphatic || [[Nylon]] [[Nylon 6|PA 6]] and [[Nylon 6-6|PA 66]] || [[Zytel]] from [[DuPont]], Technyl from [[Solvay (company)|Solvay]], Rilsan and Rilsamid from [[Arkema]], Radipol from [[Radici Group]]
|-
| [[Polyphthalamide]]s ||Semi-aromatic || PA 6T = [[hexamethylenediamine]] + [[terephthalic acid]] || Trogamid T from [[Evonik]] Industries, Amodel from [[Solvay (company)|Solvay]]
|-
| Aromatic polyamides, or [[aramid]]s || Aromatic || [[Paraphenylenediamine]] + terephthalic acid || [[Kevlar]] and [[Nomex]] from DuPont, Teijinconex, [[Twaron]] and [[Technora]] from [[Teijin Aramid]], Kermel from Kermel.
|}

All polyamides are made by the formation of an amide function to link two molecules of monomer together. The monomers can be amides themselves (usually in the form of a cyclic lactam such as [[caprolactam]]), α,ω-amino acids or a stoichiometric mixture of a diamine and a diacid. Both these kinds of precursors give a homopolymer. Polyamides are easily copolymerized, and thus many mixtures of monomers are possible which can in turn lead to many copolymers. Additionally many nylon polymers are miscible with one another allowing the creation of blends.

==Polymerization chemistry==
Production of polymers requires the repeated joining of two groups to form an amide linkage. In this case this specifically involves [[amide]] bonds, and the two groups involved are an [[amine]] group, and a terminal [[carbonyl]] component of a [[functional group]]. These react to produce a carbon-nitrogen bond, creating a singular [[amide]] linkage. This process involves the elimination of other atoms previously part of the functional groups. The carbonyl-component may be part of either a [[carboxylic acid]] group or the more reactive [[acyl halide]] derivative. The amine group and the carboxylic acid group can be on the same monomer, or the polymer can be constituted of two different [[bifunctional]] monomers, one with two amine groups, the other with two carboxylic acid or acid chloride groups.

The [[condensation reaction]] is used to synthetically produce nylon polymers in industry. Nylons must specifically include a straight chain ([[Aliphatic compound|aliphatic]]) monomer. The amide link is produced from an amine group (alternatively known as an amino group), and a [[carboxylic acid]] group. The hydroxyl from the carboxylic acid combines with a hydrogen from the amine, and gives rise to water, the elimination byproduct that is the namesake of the reaction. 

As an example of condensation reactions, consider that in living organisms, [[amino acid]]s are condensed with one another by an enzyme to form amide linkages (known as [[Peptide bond|peptides]]). The resulting polyamides are known as proteins or polypeptides. In the diagram below, consider the amino-acids as single aliphatic monomers reacting with identical molecules to form a polyamide, focusing on solely the amine and acid groups. Ignore the substituent [[Alkyl|R groups]] &ndash; under the assumption the difference between the R groups are negligible:

[[Image:2-amino-acidsb.png|class=skin-invert-image|centre|thumb|600px| The reaction of two amino acids. Many of these reactions produce long chain [[protein]]s]]

For fully aromatic polyamides or ''aramids'' e.g. [[Kevlar]], the more reactive [[acyl chloride]] is used as a monomer. The polymerization reaction with the amine group eliminates [[hydrogen chloride]]. The acid chloride route can be used as a laboratory synthesis to avoid heating and obtain an almost instantaneous reaction.<ref>{{cite web|title=Making nylon: The "nylon rope trick"| url=http://www.rsc.org/learn-chemistry/resource/res00000755/making-nylon-the-nylon-rope-trick| publisher=Royal Society of Chemistry| access-date=19 April 2015}}</ref> The aromatic [[Moiety (chemistry)|moiety]] itself does not participate in elimination reaction, but it does increase the rigidity and strength of the resulting material which leads to Kevlar's renowned strength.

In the diagram below, an [[aramid]] is made from two different monomers which continuously alternate to form the polymer chain. Aramids are aromatic polyamides:

[[Image:Kevlar_reaction.svg|class=skin-invert-image|centre|frame|The reaction of 1,4-phenyl-diamine (para-phenylenediamine) and terephthaloyl chloride to produce an aramid]]

Polyamides can also be synthesized from dinitriles using acid catalysis via an application of the Ritter reaction.  This method is applicable for preparation of [[nylon 1,6]] from [[adiponitrile]], [[formaldehyde]] and water.<ref>{{Cite journal|last1=Magat|first1=Eugene E.|last2=Faris|first2=Burt F.|last3=Reith|first3=John E.|last4=Salisbury|first4=L. Frank|date=1951-03-01|title=Acid-catalyzed Reactions of Nitriles. I. The Reaction of Nitriles with Formaldehyde1|journal=Journal of the American Chemical Society|volume=73|issue=3|pages=1028–1031|doi=10.1021/ja01147a042|issn=0002-7863}}</ref>  Additionally, polyamides can be synthesized from [[Diol|glycols]] and dinitriles using this method as well.<ref>{{Cite journal|last1=Lakouraj|first1=Moslem Mansour|last2=Mokhtary|first2=Masoud|date=2009-02-20|title=Synthesis of polyamides from p-Xylylene glycol and dinitriles|journal=Journal of Polymer Research|language=en|volume=16|issue=6|pages=681|doi=10.1007/s10965-009-9273-z|s2cid=98232570|issn=1022-9760}}</ref>

[[File:Nylon-1-6 synthesis.png|class=skin-invert-image|center|thumb|700px|Synthesis of Nylon 1,6 from adiponitrile, formaldehyde, and water using sulfuric acid as a catalyst]]

==See also==
* [[Polyamide-imide]]
*[[Pyrrole–imidazole polyamides]]

==References==
{{Reflist}}

==Further reading==
* Kohan, Melvin I. (1995). Nylon Plastics Handbook. Hanser/Gardner Publications. {{ISBN|9781569901892}}

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[[Category:Polyamides| ]]
[[Category:Thermoplastics]]
[[Category:Dielectrics]]