14219 IUPAC Gold Book - crystal polymorph 10.1351/goldbook.14219 14219 current synonyms: crystal modification, crystalline form 1 One of the different crystalline phases in which a given substance is able to crystallize. Different polymer crystal polymorphs are characterized by different crystal lattices and different packing of stems. A given polymer in its different crystal polymorphs may display the same conformation and the same chain identity period, but possibly involve packing of isochiral only or of enantiomeric helices (e.g., isotactic polypropylene in its \(\ce{\upalpha\mbox{-}form}\), \(\ce{\upbeta\mbox{-}form}\), and \(\ce{\upgamma\mbox{-}form}\); syndiotactic polypropylene, forms I and II. Polymorphs are, in such cases, isoconformational, and polymorphism is determined only by different modes of packing. In other cases, along with the packing, the local conformations of chains are different in its different crystal polymorphs. The chain identity period and the symmetry will also differ (e.g., isotactic poly(but-1-ene), crystal forms I, II, and III; syndiotactic polypropylene, crystalline forms I, III, and IV). PAC, 2011, 83, 1831. 'Definitions of terms relating to crystalline polymers (IUPAC Recommendations 2011)' on page 1845 (https://doi.org/10.1351/PAC-REC-10-11-13) https://goldbook.iupac.org/terms/view/14219/html https://goldbook.iupac.org/terms/view/14219/json https://goldbook.iupac.org/terms/view/14219/plain Citation: 'crystal polymorph' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.14219 The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using. 2026-06-29T00:25:09+00:00