https://doi.org/10.1351/goldbook.15410
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:
- 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 \({\rm{M}}_{i}\).
- The symbols \(r_{12}\) and \(r_{21}\) are often abbreviated to \(r_{1}\) and \(r_{2}\), respectively.
- 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).
See also: chain-end reactivity ratios