A series of polyesters and polyester polyurethanes were analyzed using time-of-flight secondary-ion mass spectrometry (TOF-SIMS). Analysis of poly(butylene adipate) samples produced spectra containing oligomer ions and fragments corresponding to cyclization via intramolecular ester exchange. These cyclic fragments were also observed in the spectra of polyurethane [4,4,1] samples, along with cyclic ester-urethane fragments. The mass of the diisocyanate group within the polyurethane could be determined from the mass difference between the two major fragment-ion series in the spectrum. In general, only limited fragmentation within ester or urethane repeat units was observed. The sample molecular weight for both the polyesters and polyurethanes correlated with the relative intensity of the cyclic repeat unit series ions to the Linear oligomer ions. Additionally, transesterification of polyesters and polyurethanes using trifluoroacetic acid was found to selectively cleave bonds between polyester repeat units in both types of polymers.