The invention concerns to the use, as an agent improving the thermal stability of (meth)acrylic comb polymers of a macromonomer whose formula (I) is: R-(A-O)m—(B—O)n—R′  (I) wherein both m and n are non-zero and A and B designate alkyl groups having 2 to 4 carbon atoms, but different from one another. The invention further pertains to the implementation of the polymers obtained, as agents improving the thermal stability of the plastic compositions that contain them.