Isotactic polymers are composed of isotactic macromolecules (IUPAC definition). In isotactic macromolecules all the substituents are located on the same side of the macromolecular backbone. An isotactic macromolecule consists of 100% meso diads.  Polypropylene formed by Ziegler–Natta catalysis is an isotactic polymer. Isotactic polymers are usually semicrystalline and often form a helix configuration.