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An isotactic triad (mm) is made up of two adjacent m diads, a syndiotactic triad (also spelled syndyotactic [4]) (rr) consists of two adjacent r diads, and a heterotactic triad (rm) is composed of an r diad adjacent to an m diad. The mass fraction of isotactic (mm) triads is a common quantitative measure of tacticity.
The structure of isotactic polypropylene. The structure of atactic polypropylene. Whether or not polymers can crystallize depends on their molecular structure – presence of straight chains with regularly spaced side groups facilitates crystallization. For example, crystallization occurs much easier in isotactic than in the atactic ...
The stereoselective polymerization to the isotactic was discovered by Giulio Natta and Karl Rehn in March 1954. [3] This pioneering discovery led to large-scale commercial production of isotactic polypropylene by the Italian firm Montecatini from 1957 onwards. [4] Syndiotactic polypropylene was also first synthesized by Natta.
Isotactic polypropene is a high-melting (165 °C), strong, crystalline polymer, which is used as both a plastic and fiber. Atactic polypropene is an amorphous material with an oily to waxy soft appearance that finds use in asphalt blends and formulations for lubricants, sealants, and adhesives, but the volumes are minuscule compared to that of ...
Segments of polypropylene, showing the slightly different structures of isotactic (above) and syndiotactic (below) polymers. The study of polymer thermodynamics helps improve the material properties of various polymer-based materials such as polystyrene (styrofoam) and polycarbonate.
Coordination type polymers are also stereoregular and can be isotactic or syndiotactic instead of just atactic. This tacticity introduces crystallinity in otherwise amorphous polymers. From these differences in polymerization type the distinction originates between low-density polyethylene (LDPE), high-density polyethylene (HDPE) or even ultra ...
Both isotactic and syndiotactic polypropylene are crystalline, whereas atactic polypropylene, which can also be prepared with special Ziegler–Natta catalysts, is amorphous. The stereoregularity of the polymer is determined by the catalyst used to prepare it.
In isotactic polypropylene, the molecules form a helix. Like the zigzag conformation, such helices allow a dense chain packing. Particularly strong intermolecular interactions occur when the residues of the repeating units allow the formation of hydrogen bonds , as in the case of p -aramid .