NMR and DSC studies are used to investigate the compatibility of blends of random compolymers poly(NECMM-co-MA) and poly(DNBM-co-MMA) where NECMM is the electron donor (N-ethylcarbazol-3-yl)methyl methacrylate and DNBM is the electron acceptor 2-[(3,5-dinitrobenzoyl)oxy]ethyl methacrylate. At least 14 mol % of NECMM and DNBM is needed to compatibilize PMA with PMMA. Similar blends are analyzed in which poly(NECMA-co-MA), where NECMA is the electron donor (N-ethylcarbazol-3-yl)methyl acrylate, was substituted for the NECMM-containing donor copolymer. Using NECMA, between 15 and 30 mol % donor and acceptor are required to compatibilize the blend. Blends which were prepared with high molecular weight acceptor copolymers were found to be both kinetically and thermodynamically incompatible. Almost all of the samples exhibited endothermic transitions at 200 degrees C but no accompanying phase changes. This is consistent with the interpretation of the so-called "decomplexation enthalpy" in terms of conformational relaxation in the copolymer chains within the blends.