A polymer composition with blocks of hydrophobes attached to or within the backbone of an associative thickener. The blocks are composed of two or more units of the same or different hydrophobes whereby the hydrophobe is reversibly switched between being hydrophilic and hydrophobic in nature. When the hydrophobe is rendered hydrophilic, the aqueous thickener is pourable and readily incorporated into aqueous polymer compositions. When this hydrophobe is rendered hydrophobic, the thickener performs its thickening function efficiently, especially in tinted systems. Switching is readily accomplished by adjusting the pH of the associative thickener composition and the aqueous polymer composition being thickened.