Thermoresponsive Supramolecular Dendronized Polymers

Abstract

Combining the concepts of supramolecular polymers and dendronized polymers provides the opportunity to create bulky polymers with easy structural modification and tunable properties. In the present work, a novel class of side-chain supramolecular dendronized polymethacrylates is prepared through the host-guest interaction. The host is a linear polymethacrylate (as the backbone) attached in each repeat unit with a β-cyclodextrin (β-CD) moiety, and the guest is constituted with three-fold branched oligoethylene glycol (OEG)-based first-(G1) and second-generation (G2) dendrons with an adamantyl group core. The host and guest interaction in aqueous solution leads to the formation of the supramolecular polymers, which is supported with (1)H NMR spectroscopy and dynamic light scattering measurements. The supramolecular formation was also examined at different host/guest ratios. The water solubility of hosts and guests increases upon supramolecular formation. The supramolecular polymers show good solubility in water at room temperature, but exhibit thermoresponsive behavior at elevated temperatures. Their thermoresponsiveness is thus investigated with UV/Vis and (1)H NMR spectroscopy, and compared with their counterparts formed from individual β-CD and the OEG dendritic guest. The effect of polymer concentration and molar ratio of host/guest was examined. It is found that the polar interior of the supramolecules contribute significantly to the thermally-induced phase transitions for the G1 polymer, but this effect is negligible for the G2 polymer. Based on the temperature-varied proton NMR spectra, it is found that the host-guest complex starts to decompose during the aggregation process upon heating to its dehydration temperature, and this decomposition is enhanced with an increase of solution temperature.

Thermoresponsive Supramolecular Dendrimers via Host–Guest Interactions

“…The T c s of the SDs Et‐SD1, Et‐SD2, and Me‐SD2 were determined to be 63.3, 43.9, and 72 °C, respectively. Surprisingly, these values are quite higher than those of the corresponding dendritic guests (28.2, 38.1, and 64 °C, respectively) or supramolecular dendronized polymers formed from the same dendritic guests (52.7, 34.4, and 55.2 °C, respectively) 16. EtG1‐Ada shows much lower hydrophilicity than EtG2‐Ada due to relatively larger proportion of hydrophobic adamantyl moiety within the molecule.…”

“…With the concentration decreases from 1 to 0.05 wt%, the T c of Et‐SD2 increases significantly from 38.2 to 50.2 °C. This indicates the T c s of supramolecular dendrimers are much more dependent on the solution concentration than that of the supramolecular dendronized polymers (the T c change is only 3 K with the same concentration change) 16a. The effect of salt addition on the thermoresponsiveness of supramolecular dendrimers was further examined (Figure 5, for turbidity curves see Figure S6, Supporting Information).…”

“…It has been documented that the decomplexation of the supramolecular complex or polymers takes place during their phase transitions 16, 21. Herein, the decomplexation process of these SDs was investigated by temperature‐varied 1 H NMR spectroscopy.…”

“…Dendritic guests (EtG1‐Ada, MeG2‐Ada, EtG2‐Ada) were synthesized according to our previous reports 16. Mono‐6‐deoxy‐6‐amino‐β‐CD ( 2 ) was prepared according to a literature method 17.…”

“…Although SDs have been widely reported, less attention has been paid on the preparation of SDs with thermoresponsiveness 15. Recently, we reported a series of supramolecular dendronized polymers formed through the host–guest interaction from linear polymer with cyclodextrin pendants and OEG‐based dendritic guests cored with adamantyl group 16. These supramolecular dendronized polymers show characteristic thermoresponsive behavior as their covalent counterparts, but are much easier to have tunable phase transition temperatures, which can be realized by just mixing guests of different hydrophilicities to complex with the same polymer host.…”