Living polymerization

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A living polymerization is understood to be chain polymerizations in which no termination reactions and chain transfers occur. Under "living conditions" it is possible to control molar masses with a narrow distribution. Furthermore, clearly defined polymer structures , such as block copolymers with certain sequence lengths, can be generated under these conditions . The disadvantage of this reaction procedure is the high sensitivity to impurities. For this reason, inert gas technology and absolutely dry and pure chemicals are fundamental requirements. The term living polymerisation was introduced in 1956 by Michael Szwarc for the anionic polymerisation of styrene in aprotic solvents.

In the classic case, THF serves as the solvent and naphthalene sodium is used as the initiator (1). During initiation, styrene radical anions (2) are formed, which are converted into a dianion in a dimerization (3). The particle thus has two active chain ends. During growth, the monomers are added to the dianion (4).

Anionic polymerization styrene.svg

Living polymerizations are those polymerizations that meet the following conditions:

  • The rate constant of initiation is much greater than that of propagation (k i ⋙ k p ), so that at time t = 0 the active chain ends are quantitatively available.
  • All active chains grow under the same conditions.
  • There are no chain termination reactions, nor are there chain transfer reactions.

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

In the narrower sense “living”, only anionic polymerization can be carried out. However, very similar results can also be achieved with controlled free-radical polymerization (e.g. ATRP , RAFT , NMP ) and group transfer polymerization (GTP) ( quasi-living polymerization).

literature

  • JMG Cowie, V. Arrighi: Polymers: Chemistry and physics of modern materials. CRC Press, Boca Raton 2007, ISBN 978-0-8493-9813-1 .

Individual evidence

  1. ↑ Entry on living polymerization . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.L03597 Version: 2.3.2.
  2. ^ OW Webster: Living Polymerization Methods . In: Science . tape 251 , no. 4996 , February 22, 1991, pp. 887 , doi : 10.1126 / science.251.4996.887 (English).
  3. ↑ Bernd Tieke, Makromolekulare Chemie , 3rd edition, Wiley-VCH, Weinheim, 2014, p. 103.