Editing Tacticity (section)

===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}}