Experimental Criteria for Living Polymerizations

Seven experimental criteria for living polymerizations are critically reviewed. The limitations of the use of linear plots of M̄n (or X̄;n) versus conversion and linear plots of the number of polymer chains versus conversion are illustrated by an example of alkyllithium‐initiated polymerization of styrene by incremental additions of styrene with deliberate termination (5% per incremental monomer addition). The experimental criteria of using narrow molecular weight distribution and the formation of block copolymers are illustrated with practical examples and size exclusion chromatography data. The use of the terms ‘living polymerization with reversible termination’ and ‘living polymerization with reversible chain transfer’ are proposed.