To obtain a surface-immobile and nonextractable block copolymer improved in electrostatic dissipating properties.

This inherently electrostatic dissipating block copolymer (IDP) composition is capped on its terminals with acids and comprises about 95-99.99 wt.% IDP and 0.01-5 wt.% acid terminal-capping reagent having ≥2 acid functional value. The IDP comprises about 5-85 wt.% soft segments of a polyalkylene glycol and about 15-95 wt.% hard segments obtained from a polymer reactive with hydroxyl functional values and having a glass transition temperature or a crystal melting point higher than the surrounding temperature. A modification is formed by the acid terminal-capping reagent after the IDP is formed. An alloy can be formed by adding an acid terminal-capped IDP composition to a thermoplastic base material. Methods for preparing the acid terminal capped IDP composition and the alloy are also provided.