Thermoresponsive Hyperbranched Polymers with Spatially Isomerized Groups: NMR Implication to Their Thermoresponsive Behaviors

The influence of stereochemical difference on the phase transition of thermoresponsive polymer was studied in detail in this work. To this end, we synthesized two thermoresponsive hyperbranched polymers having the almost same chemical composition but differing in the spatial distribution of the chemical groups. These samples exhibit remarkably different low critical solution temperatures (LCSTs). A detailed NMR study on the samples revealed that before the transition the chemical groups in the two samples have very different packing arrangements. A microscopic phase separation was realized in the polymer having the densely packed structure. The origin of the different LCSTs of the polymers was well explained by the entropy change due to the dehydrate/hydrate processes in the transition.