Title: monomer reactivity ratios
Long Title: IUPAC Gold Book - monomer reactivity ratios
DOI: 10.1351/goldbook.15410
Status: current

Definition
In binary copolymerization, (a) the ratio (\(r_{12}\)) of the rate constant (\(k_{11}\)) for the homopropagation of monomer \(\rm{M}_{1}\) to the rate constant (\(k_{12}\)) for the cross-propagation of the chain carrier \(\ldots -{\rm{m}}_{1}^{\ast}\) with the monomer \(\rm{M}_{2}\) and (b) the ratio (\(r_{21}\)) of the rate constant (\(k_{22}\)) for the homopropagation of monomer \(\rm{M}_{2}\) to the rate constant for the cross-propagation (\(k_{21}\)) of the chain carrier \(\ldots -{\rm{m}}_{2}^{\ast}\) with monomer \(\rm{M}_{1}\). Thus, \(r_{12} = k_{11}/k_{12}, r_{21} = k_{22}/k_{21}\).

Notes
1) The reactions involved are \[\begin{array}{l} ...-{\rm{m}}_{1}^{\ast} + {\rm{M}}_{1}\ce{->[\textit{k}_{11}]} ...-{\rm{m}}_{1}^{\ast} \\ ...-{\rm{m}}_{1}^{\ast} + {\rm{M}}_{2}\ce{->[\textit{k}_{12}]} ...-{\rm{m}}_{2}^{\ast} \\ ...-{\rm{m}}_{2}^{\ast} + {\rm{M}}_{2}\ce{->[\textit{k}_{22}]} ...-{\rm{m}}_{2}^{\ast} \\ ...-{\rm{m}}_{2}^{\ast} + {\rm{M}}_{1}\ce{->[\textit{k}_{21}]} ...-{\rm{m}}_{1}^{\ast} \\ \end{array}\] where \(\rm{M}_{1}\) and \(\rm{M}_{2}\) are the two monomers involved in the binary copolymerization and \(\ldots -{\rm{m}}_{i}^{\ast} (i = 1,2)\) denotes a chain carrier having an active site on its terminal monomer unit of type \({\rm{M}}_{i}\).
2) The symbols \(r_{12}\) and \(r_{21}\) are often abbreviated to \(r_{1}\) and \(r_{2}\), respectively.
3) The present definition ignores the penultimate-unit effect. For the definition of monomer reactivity ratios accounting for the penultimate-unit effect, see chain-end reactivity ratios (Note 3).

Related Terms
- binary copolymerization: https://goldbook.iupac.org//terms/view/15383
- chain-end reactivity ratios: https://goldbook.iupac.org//terms/view/15388
- cross-propagation: https://goldbook.iupac.org//terms/view/15393
- homopropagation: https://goldbook.iupac.org//terms/view/15404
- penultimate-unit effect: https://goldbook.iupac.org//terms/view/15413

Source
- PAC, 2008, 80, 2163. 'Glossary of terms related to kinetics, thermodynamics, and mechanisms of polymerization (IUPAC Recommendations 2008)' on page 2179 (https://doi.org/10.1351/pac200880102163)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/15410/html
- json: https://goldbook.iupac.org/terms/view/15410/json
- xml: https://goldbook.iupac.org/terms/view/15410/xml

Citation: Citation: 'monomer reactivity ratios' 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.15410
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Accessed: 2026-04-18T05:09:05+00:00