Novel cationic ring-opening polymerization of cyclodextrin: A uniform macrocyclic monomer with unique character

Abstract

Cyclodextrin (CD) derivatives were found to act as uniform macrocyclic monomers for cationic ring-opening polymerization, yielding poly[(1→4)-D- glucopyranoside]s. Interestingly, as demonstrated in the polymerization of O-permethylated α-, β-, and γ-CDs, more strained monomer (α-> β- > γ-) proved less reactive. This finding comes from the unique molecular shape of CD; the monomer having larger cavity (γ- > β- > α-) is favorable for the polymerization. In place of ordinary initiators such as oxonium salts and MeOTf, a combination of HI with an activator of ZnCl2 was found to work as the initiator effectively controlling the polymerization; the glucan obtained from O-permethylated γ-CD showed a unique molecular weight distribution, which has large, regular intervals corresponding to the molecular weight of the uniform macrocyclic monomer (= 1634).