Synthesis of polysaccharide-based block copolymers obtained by click chemistry from opened β-cyclodextrin and growth polymerization

Abstract

The synthesis of well-defined oligosaccharides via cyclodextrin (CD) ring opening is an efficient method for obtaining tailored monomers, which are then suitable for further polymerization. Starting from benzoylated β-CD, which contains seven glucose units, pure difunctionalized benzoylated heptaoses were synthesized. This approach produced heptaoligosaccharides with either azide (A) or propargyl (B) as reactive groups at the reducing and non-reducing ends with a yield between 81 and 96 %, and corresponding to α,ω-diazidoheptaose, α,ω-dipropargylheptaose, and ω-azido-α-propargylheptaose for the AA, BB, and AB monomers, respectively. A highly efficient deprotection process provided access to difunctionalized linear and polar heptasaccharides with high purity (87–99 %). The newly synthesized oligosaccharidic blocks were then polymerized via copper-catalyzed 1,3-dipolar cycloaddition leading to seven original and distinct polymers. These include unprotected (AA-BB or AB-AB) or benzoylated (AB-AB) homo- and hetero-copolymers, as well as hydrophobic blocks randomly distributed with hydrophilic ones (AB-AB) or alternating unprotected-benzoylated blocks (AA-BB). Two additional polymers were obtained by quaternization of triazole rings. Characterization by SEC, TGA, XRD, NMR, and MALDI-TOF MS revealed that a mixture of polymers containing 1–34 blocks could be obtained, with a degree of polymerization ranging from 126 to 238 sugar units and moderate to excellent yields (30–85 %).