The miscibility of blends of poly(methyl methacrylate), PMMA, and poly(ethylene oxide), PEO, oligomers was studied by temperature-modulated DSC as a function of the PMMA stereoregularity, the molecular weight and the nature of the chain ends of the PEO. The Flory-Huggins interaction parameter chi (1.2) was determined using the methodology developed by Kim and Bums and compared to those calculated from the Hildebrand solubility parameters drawn from the Van Krevelen tables. First, it turns out that the miscibility domain is larger for the a- and s-PMMA than for the isotactic isomer (as shown in previous studies) and, moreover, larger for butyl terminated PEO oligomers. The Flory-Huggins interaction parameter chi (1.2) decreases with the increase of the PEO molecular weight as well as with the syndiotacticity of the PMMA and is lower for the PEO with alkyl modified chains ends. These results highlight the non negligible contribution of the free volume to the interaction parameter and also the importance of the kinetic of the PEO crystallisation on the phase separation process.