Surface tension of liquid polybutadienes (PBD) as well as interfacial tension between them and poly(dimethylsiloxane) (PDMS) were measured in the temperature range from 25 to 150 degrees C. The measured pressure-volume-temperature (PVT) data were used for the determination of reduction parameters of pressure, volume, and temperature, in several equations of state for polymers. The reduction parameters were used for the estimates of surface tension and compared with experimental data. Interfacial tensions were used to determine Flory-Huggins interaction parameters using the Roe and Helfand theories for the system PBD-PDMS. The results obtained using both the theories were somewhat different; the difference being the least with the segment chosen as a part of molecule containing 4-5 nonhydrogen atoms. Modifications of PBD that were investigated increase the density. Maleic ester end groups increase both Surface tension and interfacial tension and bring a positive contribution to the Flory-Huggins interaction parameter (to its enthalpic component), whearas the pending maleic anhydride groups have shown the opposite effect; their negative contribution to Flory-Huiggins parameters concerns mainly its entropic component. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 169-180, 2009