The thermal behaviour of methyl methacrylate polymers (PMMA) prepared from phosphorus-containing monomers: CH 2 C(CH 3 )C(O)OCHRP(O)(OC 2 H 5 ) 2 (R H, (CH 2 ) 4 CH 3 , C 6 H 5 Br, C 1 0 H 7 ) was investigated by thermal gravimetric analysis (TGA) coupled with on-line FT-IR analysis of evolved gases. Four homopolymers and two MMA/functionalized-MMA copolymers were studied. They exhibited a thermal behaviour largely different from that encountered for PMMA. Particularly, the results revealed a major and common degradation stage near 300 o C leading to diethyl phosphite HPO(OC 2 H 5 ) 2 or diethyl phosphonate RPO(OC 2 H 5 ) 2 , aldehyde RCHO, CO, CO 2 and ethylene C 2 H 4 . Functionalization introduces high temperature degradation stages (above 750 o C) and weak points in the polymeric chain leading to a complete cracking of the polymer as no monomer molecules were found during the degradation, in contrast to PMMA. A first evaluation of the fire retardation properties of the polymers was performed by determining the limiting oxygen index (LOI).