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Polimeryzacja anionowa inicjowana reagentami przenoszącymi elektrony

Grobelny Z., Stolarzewicz A., Szczepański M., Piekarnik B.

Wiadomości Chemiczne

2008

[Z] 62, 9-10

849-873

This work describes the polymerization processes with electron-transfer reagents. Alkali metals, salts of aromatic hydrocarbons radical anions, and solutions of alkalides, i.e. salts containing alkali metal anions and complexed alkali metal cations, belong to such species [33-39]. The alkali metals transfer one electron to vinyl and diene monomers in the heterogeneous systems [54-73]. The radical anions are also able to transfer one electron [74, 77-82], however, in some cases they behave as nucleophiles [82-85] or bases [86]. These initiators are applied for the polymerization of vinyl and oxacyclic monomers in homogeneous systems. Both of them are named single-electron-transfer (SET) reagents. The alkalides are two-electron-transfer (TET) reagents. Among them potassium potassides K-, K+(18-crown-6) and K-, K+(15-crown-5)2 in tetrahydrofuran solution are mostly used for the polymerization of various monomers [53]. The initiation with these salts is usually a multistage process. An organopotassium compound is formed as the intermediate product which after the protonation by crown ether becomes the real initiator of the polymerization of vinyl monomers [92, 93, 97, 100]. The organometallic intermediate can be also protonated by the monomer or can decompose with the elimination in the systems containing oxiranes [107, 110-113] or lactones [127]. Potassium alkoxides or potassium salts of carboxylic acids, respectively, are the genuine initiators in this case. Crown ethers, known as the stable activators of chemical reactions, can participate in these processes as the reagents [107, 110, 116]. In the ring-opening reaction they form unsaturated potassium alkoxides which serve as the additional initiating agents [53, 97].