Fluorescence spectroscopy and isothermal titration calorimetry (ITC) have been used to study the intermixing in water of fluorescently labeled poly(N-isopropylacrylamides) grafted at random with low levels Of either fluorocarbon or hydrocarbon chains. In aqueous solution, the copolymers form micellar structures consisting of a loose corona of hydrated poly(N-isopropylacrylamide) chains and a hydrophobic core rich in hydrocarbon or fluorocarbon groups. From fluorescence experiments using nonradiative energy transfer between excited naphthalene and pyrene and from changes in the ratio of pyrene excimer to monomer emission intensity, it has been established that polymeric chains exchange among micelles of hydrocarbon-modified polymers, but not among hydrocarbon- and fluorocarbon-modified polymers. Hydrocarbon- or fluorocarbon-modified polymers were also added to solutions of a copolymer carrying both hydrocarbon and fluorocarbon chains, which in water forms assemblies where the fluorocarbon and hydrocarbon groups segregate into distinct nanodomains within a hydrophobic core. Evidence of fluorescence spectroscopy indicated that intermixing I of hydrocarbon-modified polymers with bis(fluorocarbon/hydrocarbon)-poly-(N-isopi-opylaci-ylainide) perturbs the hydrocarbon-rich nanodomains but not the fluorocarbon-rich ones. The conclusions were corroborated by ITC experiments, which in addition provided strong evidence that intermixing takes place among fluorocarbon-modified poly(N-isopropylacrylamides).