The phase behavior of blends of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) with random copolymers of styrene and 2-vinyl pyridine, Poly(S-co-2VP), as well as with random copolymers of styrene and 4-vinyl pyridine, Poly(S-co-4VP), has been investigated in order to estimate the values of the Flory-Huggins parameters chi(PPO),(2vp) and chi(PPO,4VP) between PPO and 2-vinyl pyridine, resp. 4-vinyl pyridine. Using previously estimated values for the Flory-Huggins parameters 0.09 < chi(S,2VP) < 0.11 and 0.30 < chi(S,4VP) < 0.35, together with the literature value of chi(S,PPO) = -0.043, the phase behavior observed as a function of the copolymer composition results in 0.11 <= chi(PPO,2VP) C 0.12 and 0.46 <= chi(PPO,4VP) < 0.48. Insight in the interaction between PPO and poly(vinyl pyridine) is of considerable interest for several nanotechnology developments, since PPO is used to improve the mechanical properties of e.g. PS-block-P4VP nanorods. (c) 2007 Elsevier Ltd. All rights reserved.