Rubber-rubber blends are used widely in industry, for example, in tire manufacture. It is often difficult to characterize interfaces in such rubber-rubber blends quantitatively because of the similarity in the chemical structure of the component rubbers. Here, a new method was suggested for the measurement of the weight fraction of the interface in rubber-rubber blends using modulated-temperature differential scanning calorimetry (M-TDSC). Quantitative analysis using the differential of the heat capacity, dCp/dT, versus the temperature signal from M-TDSC allows the weight fraction of the interface to be calculated. As examples, polybutadiene rubber (BR)-natural rubber (NR), BR-styrene-co-butadiene rubber (SBR), SBR-NR, and nitrile rubber (NBR)-NR blend systems were analyzed. The interfacial content in these blends was obtained. SBR is partially miscible with BR. The cis-structure content in BR has an obvious effect on the extent of mixing in the SBR-BR blends. With increasing styrene content in the SBR in the SBR-BR blends, the interface content decreases. NR is partially miscible with both BR and SBR. The NBR used in this research is essentially immiscible with NR. The maximum amount of interface was found to be at the 50:50 blend composition in BT-NR, SBR-BR, and SBR-NR systems. Quantitative analysis of interfaces in these blend systems is reported for the first time. (C) 2000 John Wiley & Sons, Inc.