Phase diagrams of four PEO blend systems with amorphous poly(acrylates) and poly(methacrylates) were constructed in a broad range of compositions and temperatures. The component affinity parameters were determined using data on the decrease in the melting temperature of PEO in the blends. The phase equilibrium and the melting temperature of PEO in the blends depend on the structure of the amorphous component (the presence of alpha-methyl group in the chain unit and the type of alkyl radical in the eater group), Phase diagrams with LCST were obtained in melts of the PEO-PMMA, PEO-poly(butyl acrylate), and PEO-poly(butyl methacrylate) systems. The phase diagram of the PEO-PMMA system contains UCST in the region of medium concentrations, which is situated above the glass transition temperatures of the blends. The type of phase separation in melted PEO blends is determined by structural features of the amorphous component and by a relationship between the melting temperature of the crystalline component and the glass transition temperature of the amorphous component.