The interaction of poly[2,2-bis(4-hydroxyphenyl)propanecarbonate] (PC) with phosphonic acid dialkyl esters [(RO)(2)P(O)H, where R=CH3 or CH3CH2] or with phosphoric acid triethyl ester (CH3CH2O)(3)P(O) was studied. Treatment of PC pellets with phosphonic acid dialkyl esters at 160 degrees C or with triethyl phosphate at 180 degrees C yielded phosphorus-containing oligocarbonates. The structure of the phosphorus-containing oligocarbonates was studied by P-31 NMR, H-1 NMR and C-13 NMR spectroscopy.