{"term":{"id":"15388","title":"chain-end reactivity ratio","longtitle":"IUPAC Gold Book - chain-end reactivity ratio","doi":"10.1351\/goldbook.15388","code":"15388","status":"current","synonym":"<em>synonym<\/em>: radical reactivity ratio","definitions":[{"id":1,"text":"In a binary copolymerization, the ratio of two rate constants defining the relative activity of an active center on a given type of terminal unit of a chain carrier toward one type of monomer, in the two cases where the penultimate unit of the chain carrier is identical to and different from the terminal unit.","notes":{"1":"The reactions involved are defined in accordance with the penultimate-unit effect, namely, \\[\\begin{array}{l} ...-{\\rm{m}}_{11}^{\\ast} + {\\rm{M}}_{1}\\ce{->[\\textit{k}_{111}]} ...-{\\rm{m}}_{11}^{\\ast} \\\\ ...-{\\rm{m}}_{21}^{\\ast} + {\\rm{M}}_{1}\\ce{->[\\textit{k}_{211}]} ...-{\\rm{m}}_{11}^{\\ast} \\\\ ...-{\\rm{m}}_{11}^{\\ast} + {\\rm{M}}_{2}\\ce{->[\\textit{k}_{112}]} ...-{\\rm{m}}_{12}^{\\ast} \\\\ ...-{\\rm{m}}_{21}^{\\ast} + {\\rm{M}}_{2}\\ce{->[\\textit{k}_{212}]} ...-{\\rm{m}}_{12}^{\\ast} \\\\ ...-{\\rm{m}}_{12}^{\\ast} + {\\rm{M}}_{1}\\ce{->[\\textit{k}_{121}]} ...-{\\rm{m}}_{21}^{\\ast} \\\\ ...-{\\rm{m}}_{22}^{\\ast} + {\\rm{M}}_{1}\\ce{->[\\textit{k}_{221}]} ...-{\\rm{m}}_{21}^{\\ast} \\\\ ...-{\\rm{m}}_{12}^{\\ast} + {\\rm{M}}_{2}\\ce{->[\\textit{k}_{122}]} ...-{\\rm{m}}_{22}^{\\ast} \\\\ ...-{\\rm{m}}_{22}^{\\ast} + {\\rm{M}}_{2}\\ce{->[\\textit{k}_{222}]} ...-{\\rm{m}}_{22}^{\\ast}, \\end{array}\\] where \\({\\rm{M}}_{1}\\) and \\({\\rm{M}}_{2}\\) are the two monomers involved in the binary copolymerization and \\(-{\\rm{m}}_{ij}^{\\ast} (i,j = 1,2)\\) denotes a chain carrier having an active site on its terminal monomer unit of type \\({\\rm{M}}_{j}\\) and having the adjacent, penultimate monomer unit of type \\({\\rm{M}}_{i}\\) (see chain carrier).","2":"The chain-end reactivity ratios are expressed mathematically by the equations \\[s_{1} = k_{211}\/k_{111};\\ s_{2} = k_{122}\/k_{222}\\].","3":"The monomer reactivity ratios, defined in accordance with the penultimate-unit effect, are \\[r_{112} = k_{111}\/k_{112};\\ r_{212} = k_{211}\/k_{212};\\ r_{221} = k_{222}\/k_{221};\\ r_{121} = k_{122}\/k_{121}\\]. The symbols for the monomer reactivity ratios are often abbreviated to \\(r_{1}\\), \\(r_{1}^{\\prime}\\), \\(r_{2}\\), \\(r_{2}^{\\prime}\\), respectively (see monomer reactivity ratios for the definitions of \\(r_{1}\\) and \\(r_{2}\\) ignoring the penultimate-unit effect)."},"links":[{"term":"binary copolymerization","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/15383"},{"term":"monomer reactivity ratios","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/15410"},{"term":"penultimate-unit effect","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/15413"}],"sources":["PAC, 2008, 80, 2163. 'Glossary of terms related to kinetics, thermodynamics, and mechanisms of polymerization (IUPAC Recommendations 2008)' on page 2168 (https:\/\/doi.org\/10.1351\/pac200880102163)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/15388\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/15388\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/15388\/plain"},"citation":"Citation: 'chain-end reactivity ratio' 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.15388","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":"2026-06-28T21:16:38+00:00"}}