Editing Tacticity (section)

==Polymers==

[[File:IUPAC definition for a tactic block in a polymer.png|thumb|right|550px|link=https://doi.org/10.1351/goldbook.T06242|IUPAC definition for a tactic block in a polymer]]

===Isotactic polymers===
Isotactic polymers are composed of isotactic macromolecules (IUPAC definition).<ref>[[IUPAC]] [http://www.iupac.org/reports/1996/6812jenkins/molecules.html macromolecular glossary] {{webarchive|url=https://web.archive.org/web/20080211121815/http://www.iupac.org/reports/1996/6812jenkins/molecules.html |date=2008-02-11 }}</ref> In isotactic macromolecules, all the substituents are located on the same side of the macromolecular backbone. An isotactic macromolecule consists of 100% {{nobr|m diads}}, though IUPAC also allows the term for macromolecules with at least 95% {{nobr|m diads}} if that looser usage is explained.<ref name="danrotp" /> [[Polypropylene]] formed by [[Ziegler–Natta catalyst|Ziegler–Natta catalysis]] is an example of an isotactic polymer.<ref>Stevens, P. S. Polymer Chemistry: An Introduction, 3rd ed.; Oxford Press: New York, 1999; pp 234-235</ref> Isotactic polymers are usually [[semicrystalline]] and often form a helix configuration.{{fact|date = December 2024}}

:[[File:Isotactic-A-2D-skeletal.png|400px|isotactic polymers]]
:[[File:Isotactic-polypropylene-3D-balls.png|400px|isotactic polypropylene]]

===Syndiotactic polymers===
In syndiotactic or '''syntactic''' macromolecules the substituents have alternate positions along the chain. The macromolecule comprises 100% {{nobr|r diads}}, though IUPAC also allows the term for macromolecules with at least 95% {{nobr|r diads}} if that looser usage is explained. Syndiotactic [[polystyrene]], made by [[metallocene catalysis polymerization]], is crystalline with aa [[melting point]] of 161&nbsp;°C. [[Gutta percha]] is also an example syndiotactic polymer.<ref>Brandrup, Immergut, Grulke (Editors), Polymer Handbook 4th edition, Wiley-Interscience, New York, 1999. VI/11</ref>

:[[File:Syndiotactic-2D-skeletal.png|400px|syndiotactic polymers]]
:[[File:Syndiotactic-polypropylene-3D-balls.png|400px|syndiotactic polypropylene]] 

===Atactic polymers===
{{refimprove section|date = December 2024}}
In atactic macromolecules the substituents are placed randomly along the chain. The percentage of {{nobr|m diads}} is understood to be between 45 and 55% unless otherwise specified, but it could be any value other than 0 or 100% if that usage is clarified.<ref name="danrotp" /> With the aid of spectroscopic techniques such as [[Nuclear magnetic resonance|NMR]], it is possible to pinpoint the composition of a polymer in terms of the percentages for each triad.<ref>{{cite thesis|last=Noble|first=Benjamin Brock|date=August 2016|title=Towards Stereocontrol in Radical Polymerization|publisher=Australian National University|doi=10.25911/5d723e5a7c412 |s2cid=98943399 |url=https://pdfs.semanticscholar.org/43d8/f20be925bf52e1fa209888b7de793149a4e8.pdf|access-date=2019-07-13|archive-url=https://web.archive.org/web/20190714011621/https://pdfs.semanticscholar.org/43d8/f20be925bf52e1fa209888b7de793149a4e8.pdf|archive-date=2019-07-14|url-status=dead}}</ref>{{better source|date = December 2024}}<!--THERE IS NO EXCUSE TO USE A DISSERTATION AS CITATION FOR SUCH A GENERAL STATEMENT.-->

:[[File:Atactic-2D-skeletal.png|400px|atactic polymers]]

Polymers that are formed by [[free-radical polymerization|free-radical mechanisms, such]] as [[polyvinyl chloride]] are usually atactic.{{fact|date = December 2024}} Due to their random nature atactic polymers are usually [[amorphous]].{{fact|date = December 2024}} In ''hemi-isotactic macromolecules'' every other repeat unit has a random substituent.{{fact|date = December 2024}}

Atactic polymers such as [[polystyrene]] ([[Polystyrene|PS]]) are technologically very important.{{fact|date = December 2024}} It is possible to obtain syndiotactic polystyrene using a [[Kaminsky catalyst]],<ref>{{cite journal|doi=10.1021/ma00206a010 |title=Syndiotactic polymerization of styrene with supported Kaminsky-Sinn catalysts |date=1990 |last1=Soga |first1=Kazuo |last2=Nakatani |first2=Hisayuki |journal=Macromolecules |volume=23 |issue=4 |pages=957–959 |bibcode=1990MaMol..23..957S }}</ref> but most industrial polystyrene produced is atactic.{{fact|date = December 2024}} The two materials have very different properties because the irregular structure of the atactic version makes it impossible for the polymer chains to stack in a regular fashion: whereas syndiotactic PS is a semicrystalline material, the more common atactic version cannot crystallize and forms a ''glass'' instead.{{fact|date = December 2024}} This example is quite general in that many polymers of economic importance are atactic glass formers.{{fact|date = December 2024}}

===Eutactic polymers===
In eutactic macromolecules, substituents may occupy any specific (but potentially complex) sequence of positions along the chain.{{fact|date = December 2024}} Isotactic and syndiotactic polymers are instances of the more general class of eutactic polymers, which also includes heterogeneous macromolecules in which the sequence consists of substituents of different kinds (for example, the side-chains in proteins and the bases in nucleic acids).{{fact|date = December 2024}}