Four new ester carbonate monomers were prepared by reaction of the mono(methylcarbonate) of bisphenol A with dimethyldiphenylsilane, tetraphenylsilane, 2,6-naphthalene and trans-1,4-cyclohexane diacid chlorides at 0 degrees C in the presence of an acid acceptor, triethylamine. Monomers were characterized by melting point, H-1 and C-13 nuclear magnetic resonance (n.m.r.), infra-red (i.r.) spectroscopy, mass spectrometry, elemental analysis and thermogravimetric analysis (t.g.a.). Self-polycondensation of monomers in the presence of titanium tetraisopropoxide catalyst resulted in the formation of poly(ester carbonate)s. The structural characterization of polymers was carried out by H-1 and C-13 n.m.r. and i.r. spectroscopy. Thermal properties were evaluated by differential scanning calorimetry and t.g.a. and crystallinity by X-ray diffraction.