Chemical reactions occurring during reactive melt mixing of equimolar blend of poly(bisphenol-A carbonate) and poly(ethylene 2,6-naphthalate) at 280 °C in presence of a catalyst, were studied. Beside expected direct "inner-inner" ester-carbonate and outer-inner exchange reactions, consecutive reactions that lead to the elimination of CO2 and ethylene carbonate from backbone, were also detected. The composition and the architecture of the formed copolymers change as the mixing time increases. Initial PC-PEN block copolymers formed at lower mixing time (2 min) evolve towards the formation of naphthalate based random copoly(ester-ether)s at reaction time higher than 45 min, owing to total elimination of carbonate units. Determination of composition and microstructure of copolymers formed was attempted by (1H and 13C)-NMR analyses applying appropriate chemical microstructural model. Dyads and triads sequences determined here give detailed information on the change in the molar fractions of the sequences with increasing the reaction time. DSC analysis shows that block copolymer formed at 2 min mixing present two glass transition (Tg) temperatures close to those of initial homopolymers, whereas the other ones show a single Tg that changes as a function of their dyads molar compositions. Thermogravimetric analysis show that the more thermally stable copolymers are random copoly(ester-ether)s formed at higher reaction time.