The synthesis of poly(styrene-maleic anhydride) copolymers by frontal polymerization is reported. The propagating front can be achieved if the mole fraction of styrene (St) is 0.3 less than or equal to St less than or equal to 0.7 in the feed. Depending on the St/MA mole ratio alternating St-MA-St-MA copolymers (St/MA less than or equal to 1) or (St-MA)(n)-(St-St-St)(m) block copolymers (St/MA > 1) are formed. The microstructure of the copolymers obtained was estimated by means of C-13 NMR spectroscopy.