AbstractThe change in conductivity with concentration has been studied for living poly(methyl methacrylate) at −78°C in tetrahydrofuran as solvent and using lithium, sodium, and potassium as gegen‐ions. The experimental conditions of MMA polymerizations have been similar to those used to prepare monodisperse samples. Biphenyl‐alkali metal complexes have been used as initiators. Their dissociation constants have been determined at 25°C with values 2.7·10−6, 0.83·10−6, and 0.18·10−6mole/l., for Li⊕, Na⊕, and K⊕as gegen‐ions, respectively.Log Λvs.log c plots for living polymers yield straight lines with slopes varying between −0.17 and −0.28, depending on the cation. At dilute concentrations the slopes sharply jump up to −0.50. The values for the dissociation constants, calculated by FUOSS method, are 4.4·10−10and 2.1·10−10mole/l., with Li⊕and K⊕as gegen‐ions, respectively. In the case of Na⊕a quantitative estimation of Kdwas not possible, but, qualitatively, it appears t