{"term":{"id":"12744","title":"beta relaxation","longtitle":"IUPAC Gold Book - beta relaxation","doi":"10.1351\/goldbook.12744","code":"12744","status":"current","synonym":"<em>synonym<\/em>: β-relaxation","definitions":[{"id":1,"text":"Second-highest-temperature or second-lowest-frequency relaxation in the loss curve of a polymer.","notes":{"1":"For an amorphous polymer, the \\(\\upbeta\\)-relaxation is generally related to localised motions involving only a few atoms of a polymer chain or is due to side-group motion.","2":"In some partially crystalline polymers, the \\(\\upbeta\\)-relaxation corresponds to the glass-transition temperature (see Note 2 of definition alpha relaxation)."},"links":[{"term":"alpha relaxation","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/12740"},{"term":"amorphous polymer","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/12742"},{"term":"loss curve","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/12781"}],"sources":["PAC, 2013, 85, 1017. 'Glossary of terms relating to thermal and thermomechanical properties of polymers (IUPAC Recommendations 2013)' on page 1019 (https:\/\/doi.org\/10.1351\/PAC-REC-12-03-02)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/12744\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/12744\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/12744\/plain"},"citation":"Citation: 'beta relaxation' 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.12744","license":"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.","collection":"If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .","disclaimer":"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.","accessed":"2026-07-13T10:26:14+00:00"}}