Radical polymerization by a supramolecular catalyst: cyclodextrin with a RAFT reagent

Supramolecular catalysts have received a great deal of attention because they improve the selectivity and efficiency of reactions. Catalysts with host molecules exhibit specific reaction properties and recognize substrates via host-guest interactions. Here, we examined radical polymerization reactions with a chain transfer agent (CTA) that has alpha-cyclodextrin (alpha-CD) as a host molecule (alpha-CD-CTA). Prior to the polymerization of N,N-dimethylacrylamide (DMA), we investigated the complex formation of alpha-CD with DMA. Single X-ray analysis demonstrated that alpha-CD includes DMA inside its cavity. When DMA was polymerized in the presence of alpha-CD-CTA using 2,2'-azobis[2-(2-imidazolin-2-yl)propane dihydrochloride (VA-044) as an initiator in an aqueous solution, poly(DMA) was obtained in good yield and with narrow molecular weight distribution. In contrast, the polymerization of DMA without alpha-CD-CTA produced more widely distributed polymers. In the presence of 1,6-hexanediol (C-6 diol) which works as a competitive molecule by being included in the alpha-CD cavity, the reaction yield was lower than that without C-6 diol.