Regulating polystyrene glass transition temperature by varying the hydration levels of aromatic ring/Li interaction.

Polymer properties can be altered lithium ion doping, whereby adsorbed Li binds with HO within the polymer chain. However, direct spectroscopic evidence of the tightness of Li/HO binding in the solid state is limited, and the impact of Li on polymer sidechain packing is rarely reported. Here, we investigate a polystyrene/HO/LiCl system using solid-state NMR, from which we determined a dipolar coupling of 11.4 kHz between adsorbed Li and HO protons. This coupling corroborates a model whereby Li interacts with the oxygen atom in HO charge affinity, which we believe is the main driving force of Li binding. We demonstrated the impact of hydrated Li on sidechain packing and dynamics in polystyrene using proton-detected solid-state NMR. Experimental data and density functional theory (DFT) simulations revealed that the addition of Li and the increase in the hydration levels of Li, coupled with aromatic ring binding, change the energy barrier of sidechain packing and dynamics and, consequently, changes the glass transition temperature of polystyrene.