To provide a process for producing acrylic resins by which the reaction efficiency is increased and the reaction uniformity is markedly improved by controlling the fluctuation in the amount of extrusion for an extruder having a pressure control mechanism.

A reaction extruder includes the first extruder in which a sold resin material is plasticized, auxiliary raw materials for the first step reaction are supplied for reaction, the second extruder in which auxiliary raw materials for the second step reaction are fed into the molten resin supplied from the first extruder for reaction and/or deaeration, a part connecting the outlet for the resin of the first extruder with the raw material inlet of the second extruder and a pressure control mechanism for the inside of the first reactor. The reaction extruder achieves a desired reaction rate by regulating the various reaction parameters to satisfy formula (1). The scheme is particularly effective for producing imide resins by the reaction of acrylic resins with an imidization agent. In the formula, the pressure is P PMa; reaction reagent concentration is a C part: maximum temperature of the extruder is QC; reaction time is t min.