Block and Graft Copolymers by Successive Addition

Anionic polymerization of ethylene oxide by living carbanions of polystyrene was first carried out by Szwarc295. A limited number of methods have been reported in the preparation of A-B and A-B-A copolymers in which B was polystyrene and A was poly(oxyethylene)296-298. The actual procedure was to allow ethylene oxide to polymerize in a vacuum system at 70 °C with the polystyrene anion initiated with cumyl potassium in THF299. The yields of pure block copolymers are usually limited to about 80% because homopolymers are formed300.  

In a similar manner polyisoprene-polyethylene oxide block copolymers can prepared301. It is surprising that the poly(methyl methacrylate) anion can be successfully used for the polymerization of ethylene oxide without chain transfer302. Graft copolymers are also prepared by successive addition of ethylene oxide to the poly- 

An alternative procedure consisted of trichloroacetylation of the end groups and redox initiation with sulfur dioxide and pyridine309. In these two methods the block efficiency was not high. An improved method was proposed by Furukawa in which a macromolecular initiator is prepared from polyetherglycol and azobiscyanovaleroyl dichloride310 311.  

Cationic polymerization of ethylene oxide is accompanied by depolymerization and oligomerization. It has been reported that ethylene oxide polymerized cation-ically with the living dication of tetrahydrofuran and a surface active material was obtained290.  

Block or graft copolymem can be obtained by cationic polymerization of THF with macromolecular initiators. The recommended groups for the initiation are the dioxolenium cation, the acyl cation and the super acid ester, each of which can be introduced into the backbone polymer by reaction with silver salts of strong acids. Introduction of the dioxolenium group into polystyrene was carried out by the following route32  

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