The phase equilibrium in the binary systems based on hydroxyl-terminated butadienes and diglycidyl ether of bisphenol A has been studied in wide ranges of temperature and compositions of the solution. The analysis of the obtained experimental and calculated data shows that the molecular weight, content of hydroxyl groups, functionality of the oligomer, and the presence of bromine in the oligomer affect the level of the thermodynamic compatibility. An increase in the content of hydroxyl groups and bromine results in an increase in the compatibility of the components. The results obtained are interpreted in terms of the Flory-Huggins theory. The correlation between the phase boundary concentrations and an upper critical solution temperature and solubility parameters of the oligobutadienes has been established.