Editing Copolymer (section)

==Reactivity ratios==
The ''reactivity ratio'' of a growing copolymer chain terminating in a given monomer is the ratio of the [[reaction rate constant]] for addition of the same monomer and the rate constant for addition of the other monomer. That is, <math>r_1 = \frac{k_{11}}{k_{12}}</math> and <math>r_2 = \frac{k_{22}}{k_{21}}</math>, where for example <math>k_{12}</math> is the rate constant for propagation of a polymer chain ending in monomer 1 (or A) by addition of monomer 2 (or B).<ref name=Cowie/>

The composition and structural type of the copolymer depend on these reactivity ratios r<sub>1</sub> and r<sub>2</sub> according to the [[Mayo–Lewis equation]], also called the '''copolymerization equation''' or '''copolymer equation''',<ref>{{cite journal | last1 = Mayo | first1 = Frank R. | author-link = Frank R. Mayo | author-link2 = Frederick M. Lewis | last2 = Lewis | first2 = Frederick M. | year = 1944 | title = Copolymerization. I. A Basis for Comparing the Behavior of Monomers in Copolymerization; The Copolymerization of Styrene and Methyl Methacrylate | journal = [[J. Am. Chem. Soc.]] | volume = 66 | issue = 9| pages = 1594–1601 | doi = 10.1021/ja01237a052 }}</ref><ref name=Cowie/> for the relative instantaneous rates of incorporation of the two monomers.

<math>\frac{\mathrm{d} \left[ \mathrm{M}_1 \right]}{\mathrm{d} \left[ \mathrm{M}_2 \right]} = \frac{\left[ \mathrm{M}_1 \right] \left( r_1 \left[ \mathrm{M}_1 \right] + \left[ \mathrm{M}_2 \right] \right)}{\left[ \mathrm{M}_2 \right] \left( \left[ \mathrm{M}_1 \right] + r_2 \left[ \mathrm{M}_2 \right] \right)}</math>