Living polymerization

In a living polymerization is understood polymerizations, for which there is no termination reaction. By " living conditions " the control of molecular weights with narrow distribution is possible. Furthermore, under these conditions, can be clearly defined polymer structures, as for example, produce block copolymers with certain sequence lengths. The disadvantage of this reaction is the high sensitivity to impurities. For this reason, Schutzgastechnik and absolutely dry, as well as pure chemicals fundamental conditions.

The term living polymerization ' was introduced in 1956 by Michael Szwarc for the anionic polymerization of styrene in aprotic solvents.

As living polymerizations such polymerizations are known that meet the following conditions:

• The rate constant of initiation of the reaction is much greater than that of the Propagationsschrittes (ki >>> KP), so that at time t = 0 are present, the active chain ends quantitatively.
• All active chains grow under the same conditions.
• There is no chain termination reactions, nor is there a chain transfer reactions.

After polymerization, the chain ends remain active and can be functionalized by reaction with specific termination reagents.

In a narrower sense "alive" only the anionic polymerization can be performed. Very similar results are also with the controlled free radical polymerization (eg ATRP, RAFT, NMP ) and the group transfer polymerization (GTP ) reached ( quasi- living polymerization ).