Supramolecular Linear-g-Hyperbranched Graft Polymers: Topology and Binding Strength of Hyperbranched Side Chains

Complex, reversible hyperbranched graft polymer topologies have been obtained by spontaneous self-assembly. Well-defined adamantyl- and beta-cyclodextrin-functionalized polymers were employed to generate linear-g-(linear-hyperbranched) supramolecular graft terpolymers. For this purpose the synthesis of monoadamantyl-functionalized linear polyglycerols (Ada-linPG) and hyperbranched polyglycerols (Ada-hbPG) as well as poly(ethylene glycol)-block-linear polyglycerol (Ada-PEG-b-linPG) and poly(ethylene glycol)-block-hyperbranched poly-(glycerol) (Ada-PEG-b-hbPG) block copolymers was established. Isothermal titration calorimetry (ITC) with beta-cyclodextrin revealed a shielding effect of hyperbranched polyglycerol for the adamantyl functionality, which was significantly less pronounced when using a linear spacer chain between the adamantyl residue and the hyperbranched polyglycerol block. Additionally, well-defined poly(2-hydroxypropylamide) (PHPMA) with pendant beta-cyclodextrin moieties was synthesized via RAFT polymerization and sequential postpolymerization modification. Upon mixing of the beta-cyclodextrin-functionalized PHPMA with Ada-PEG-b-hbPG, a supramolecular linear-g-(linear hyperbranched) graft terpolymer was formed. The self-assembly was proven by ITC, diffusion-ordered NMR spectroscopy (DOSY), and fluorescence correlation spectroscopy (FCS).