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Abstract The determination of reactivity ratios is simplified by using an excess of one monomer (M 1 ) at a time large enough that the copolymers will have a very small content of the other monomer (M 2 ). In this case chain propagation takes place almost exclusively by addition to polymer radicals with a terminal M 1 ‐unit (P ) and monomer consumption by propagation of P may be neglected. One reactivity ratio (r 1 ) is obtained from monomer conversions by means of a simple integrated equation which is valid up to high conversions. A calculation is proposed in order to account for the neglected propagation via P . The other reactivity ratio (r 2 ) is obtained from copolymerizations with excess M 2 . As the new method uses an integrated form of the MAYO equation it permits the determination of monomer conversions directly by gas chromatography of unreacted monomers. Thus, if desired, analysis of copolymers can be avoided. The gas chromatographic method has been tested with the radical copolymerization of styrene and methyl methacrylate. In ternary and quaternary copolymerizations the new method offers particular advantages.
V. Jaacks (1972) studied this question.