1. Introduction Nanostructured polymer blends are polymeric sys- tems in which the dispersed-phase domains exhibit length scales of 100 nm or less. Usually those poly- mer blends are referred to as nanoblends [1]. Although, the same terminology can be found in the literature to describe mixture of inorganic nanopar- ticles with polymer, which should mostly be referred as nanocomposites [2]. Nanoblends have been devel- oped to be applied in electronic, membrane, sensing probes and optical applications [3–5]. There are sev- eral approaches to obtain nanoblends. Reactive extru- sion has been used to produce nanostructured poly- mer blends based on polyamides [1]. In situ blend polymerization has also been used to develop sev- eral kind of nanoblends [6, 7]. Solution casting blending has been preferred to obtain nanoblends for those systems with poor thermo-mechanical sta- bility to be prepared by melt mixing [8, 9]. The most used method to prepare nanoblends is by melt blend- ing [10, 11]. Polymer nanoblends can be designed by two approaches, one considering thermodynam- ics aspects and the other one considering microrhe- ology basis [12]. The interaction energy density parameter (B) can be used to predict polymer blends phase separation with disperse domains in the nano- scale, as proposed by Paul and Bucknall [13]. B parameter is strictly related to the Flory-Huggins 164 PMMA/SAN and SAN/PBT nanoblends obtained by blending extrusion using thermodynamics and microrheology basis L. C. Costa 1* , A. Ternes Neto 1 , E. Hage 2 1 Materials Science and Engineering Graduate Program, Federal University of São Carlos 13565-905 São Carlos, SP, Brazil 2 Department of Materials Engineering, Federal University of São Carlos 13565-905 São Carlos, SP, Brazil Received 1 August 2013; accepted in revised form 22 October 2013 Abstract. Styrene-Acrylonitrile (SAN) copolymer has been blended to poly(methyl methacrylate) (PMMA) and to poly(butylene terephthalate) (PBT) to obtain polymer nanoblends based on thermodynamics and microrheological aspects. PMMA/SAN and SAN/PBT blends show miscibility windows for a specific range of acrylonitrile (AN) content in the SAN copolymer. The phase diagram for both blends has been calculated using the interaction energy density parameter B as func- tion of AN content in the SAN. A critical interaction energy density parameter, B crit , was also calculated to find the misci- bility window for both SAN blends. For some of the used SAN in the blends it was possible to obtain nanoblends as the AN content would allow B values close to the B crit . For immiscible PMMA/SAN and SAN/PBT blends the disperse particle size was predicted using suitable equations and it was observed by transmission electron microscopy (TEM). Acrylic copoly- mers were used as compatibilizer to modify the interfacial tension and reduce the disperse phase dimensions. The compat- ibilizer has shown strong effect by reducing the interfacial tension and by preventing the coalescence effect. The compati- bilized blends have shown disperse particle size within the nanoscale. Keywords: nanomaterials, polymer blends and alloys, nanoblends, compatibilization eXPRESS Polymer Letters Vol.8, No.3 (2014) 164–176 Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2014.20 * Corresponding author, e-mail: lidiane@ufscar.br © BME-PT