Thermoresponsive supramolecular dendronized copolymers with tunable phase transition temperatures

Abstract

Supramolecular copolymerization from a mixture of comonomers with different hydrophilicities may offer an easy and convenient access to form thermoresponsive supramolecular copolymers with varied phase transition temperatures by simply varying ratios of the comonomers. Herein, supramolecular dendronized copolymers (SDCPs) were constructed via host–guest interaction from a linear polymer carrying β-cyclodextrin units (the host) and a mixture of two adamantyl-cored second generation oligo(ethylene glycol) dendrons (the guests). The phase transition temperatures of these SDCPs can be tuned continuously in the range of 34–56 °C by varying the ratios of the dendritic guests. To check the possible effects of steric hindrance and hydrophilicity of the guests on the supramolecular complexation, isothermal titration calorimetry was applied to follow the complexation process of the first (G1) and second generation (G2) dendritic guests. Proton NMR spectroscopy was utilized to follow dehydration and collapse processes of SDCPs. It was found that the dehydration and collapse of the OEG units initiated decomposition of the dendritic guests from the supramolecular copolymers, and the more hydrophobic guest dissociated at a much lower temperature than that for the more hydrophilic one.