The melting temperatures of five emulsion polymerized polybutadienes containing varying amounts of trans‐1,4 units were determined. Since slow heating rates were used subsequent to the initial crystallization, melting temperatures were observed that were appreciably higher than previously indicated. The data were analyzed according to the theory of the melting point depression of copolymers, and a lower limit for the heat of fusion per 1,4‐trans unit of 18.5 cal./g. was obtained. This value is larger than that for natural rubber and explains why calorimetric measurements of the heat of fusion apparently give abnormally high values. The index of refraction and densities of the amorphous polymers were determined at 25°C. and the specific refractivities found to be constant and independent of polymer constitution in the composition range studied.