Ion-Size-Dependent Dissociation Pathways and Chain Dynamics in Telechelic Ionomers of Poly(propylene glycol)

The dissociation/reassociation kinetics and chain dynamics of telechelic ionomers synthesized from carboxylate-terminated poly(propylene glycol) with various alkali metal counterions (Na+, K+, Rb+, Cs+) are investigated to clarify their ion-size-dependent dissociation pathways. By combining broadband dielectric spectroscopy (BDS) and linear viscoelasticity (LVE), we find that the ionomers with Rb+ and Cs+ counterions exhibit clear Maxwellian-type terminal relaxation, indicating a uniform relaxation rate of all telechelic chains, likely through the dissociation of ion pairs as stickers. In comparison, ionomers with Na+ and K+ counterions exhibit sticky-Rouse-like relaxation behavior in the terminal region. This feature, given that each chain has two uniform stickers, is attributed to the continuous relaxation of a sequence of chains through dissociations of quadrupoles or even larger clusters that connect these chains.