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In page Tacticity:

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Isotactic polymers are composed of isotactic macromolecules (IUPAC definition).[1] In isotactic macromolecules, all the substituents are located on the same side of the macromolecular backbone. An isotactic macromolecule consists of 100% m diads, though IUPAC also allows the term for macromolecules with at least 95% m diads if that looser usage is explained.[2] Polypropylene formed by Ziegler–Natta catalysis is an example of an isotactic polymer.[3] Isotactic polymers are usually semicrystalline and often form a helix configuration.[citation needed]