Two reaction pathways for synthesis of high molar mass (M w above 50 000 g/mol) aliphatic-aromatic poly(estercarbonate)s were elaborated. Simple organic carbonates such as dimethyl carbonate or propylene carbonate were used as carbonate linkage sources and dimethyl terephthalate as the precursor of ester linkages. 1,4-Butanediol, 1,5-pentanediol, 1,6-hexanediol and 1,10-decanediol were used as diol monomers. To adjust the carbonate units content in the copolymer, solid alkylene bis(methylcarbonate) was used as a semiproduct instead of volatile dimethyl carbonate. In case of usage propylene carbonate as a starting material the process can be carried out in one pot without the need for isolation of the semiproduct. The obtained copolymers based on 1,4-butanediol, containing ca. 50 mol.% of carbonate units exhibited better mechanical strength (37 MPa) than commercially available aliphatic-aromatic copolyester Ecoflex ® keeping the thermal properties at the same level.