In this study, we designed an ABA-type copolymer physically end-cross-linked by polyoxometalate and developed a versatile and robust pathway to tune its structural and rheological properties. The copolymer precursors are composed of a central poly(n-butyl acrylate) (nBA) block with DP congruent to 100 and two short vinyl imidazole (VIm) moieties as chain ends. Phase segregation occurs gradually for the precursors with an increase of the number of Vim per end, N-VIm, from 1 to 7.6, and clear segregation is observed for precursor with the highest N-VIm = 7.6, using small-angle X-ray scattering. For those precursors having N-VIm <= 4.6, introduction of a small amount of silicotungstic acid, H-4[SiW12O40], induces phase segregation, owing to a strong electrostatic attraction between [SiW12O40](4-) ion and protonated Vim monomer. As a result, the copolymer chains are physically cross-linked, forming thermoplastic copolymers, for which the size of core, plateau modulus, and solid-to-liquid transition temperature can be tuned in wide ranges by the content of silicotungstic acid. The solid-to-liquid transition temperature is controlled by an energy barrier for dissociation of the VIm end moieties. Analysis of the solid-to-liquid transition temperature enables us to determine a scaling relationship between the energy barrier and the size and degree of protonation of the end moiety. The near-proportionality between the activation energy E-a and the length of the end moiety suggests a strong motional coupling of the ionic associations belonging to the same end moiety.