Cyclodextrin-based hyperbranched polymers by acyclic diene metathesis polymerization of an AB_n monomer: molecule design, synthesis, and characterization

A novel cyclodextrin-based hyperbranched polymer (HBP) was synthetized via acyclic diene metathesis (ADMET) polymerization in homogeneous water/organic mixtures. A modified α-cyclodextrin (α-CD) molecule with one electron-rich terminal alkene and many electron-poor acrylates was first prepared through the esterification reaction, and then utilized as an AB_n-type monomer for subsequent ADMET polymerization between alkene and acrylate using the second generation Hoveyda-Grubbs catalyst, yielding HBP with the reaction time prolonged. The chemical structures of monomer and HBP were characterized by elemental analysis, IR, gel permeation chromatography with multiangle laser light scattering, and NMR measurements. The degree of branching was determined by using ¹H NMR spectroscopy and the values ranged from 0.51 to 0.42. Influence of the molecular weight on the properties (thermal stability and solubility) was also investigated. The resulting HBPs showed the good thermal stability, and higher molecular weight resulted in higher decomposition temperature from 361 °C to 383 °C. These thermally stable HBPs also displayed the excellent solubility in aprotic polar solvents.