Group transfer polymerization
A group transfer polymerization (abbreviated GTP) is the polymerization of acrylic monomers with silyl ketene acetals . A shift of the silyl group ( group transfer ) to the chain end and formation of a new silyl ketene acetal takes place. As monomers mainly come acrylic acid , methacrylic acid , acrylic , methacrylonitrile , and also dialkyl and Dienoates and Trienoate used. Silyl ketene acetals of methacrylates or similar compounds, which form stable silyl ketene acetals, are normally used as initiators that are built into the polymer. The concentration of the initiator controls the degree of polymerization . The polymerization reaction requires a catalyst . For this purpose, on the one hand, anionic fluorides , azides or cyanides and, on the other hand, Lewis acids such as zinc chloride or aluminum dialkyl chlorides are used. Based on the initiator, about 10% catalyst is used.
The exact mechanism of the group transfer polymerization has not yet been elucidated. However, it can be assumed that the mechanism corresponds to that of a Mukaiyama-Michael reaction . The group transfer polymerization is also known as living polymerization (or living polymerization ) because, unlike other types of polymerization (with the exception of anionic polymerization), it does not have a termination reaction.
The GTP must be carried out in a strictly water- and oxygen-free environment, and therefore water- and air-free solvents such as toluene or tetrahydrofuran are also used as solvents . In order to interrupt the polymerization reaction, the reaction mixture is mixed with proton suppliers such as water or alcohols .
Products obtained by GTP are of technical interest as dispersants , rheological additives and for toners .
Group transfer polymerization was first discovered by Owen Webster.
Individual evidence
- ^ OW Webster, WR Hertler, DY Sogah, WB Farnham, TV RajanBabu: Group-transfer polymerization. 1. A new concept for addition polymerization with organosilicon initiators. In: J. Am. Chem. Soc. 1983, 105, pp. 5706-5708, doi : 10.1021 / ja00355a039 .
literature
- Manfred Dieter Lechner, Klaus Gehrke, Eckhard H. Nordmeier: Macromolecular Chemistry: A textbook for chemists, physicists, materials scientists and process engineers. 4th edition, Birkhäuser Verlag, Basel, Boston, Berlin 2010 p. 102, ISBN 978-3-7643-8890-4 .
- Volker Wiskamp: Introduction to Macromolecular Chemistry. Harri Deutsch, Thun, Frankfurt 1999 pp. 21-22, ISBN 3-8171-1609-8 .
- Manfred T. Reetz , Ralph Ostarek, Karl-Erwin Piejko, Dieter Arlt, Bruno Bömmer: Group transfer polymerization of acrylic acid esters with alkylthio- or arylthiosilanes as initiators. In: Angewandte Chemie . 1986, 98, pp. 1116-1118, doi : 10.1002 / anie.19860981222 .