A ternary blend system of polystyrene (aPS), poly(alpha-methyl styrene) (PalphaMS), and poly(4-methyl styrene) (P4MS) (blends of three styrenic homopolymers of similar molecular structures) was investigated by using differential scanning calorimetry (DSC), polarized-light optical microscopy (POM), scanning electron microscopy (SEM), and solid-state C-13 cross-polarization/magic angle spinning nuclear magnetic resonance (CP/MAS NMR). This ternary system of aPS/PalphaMS/P4MS exhibits a small miscibility loop only at relatively high percentages of PalphaMS (greater than or equal to 80%), while most of the aPS/PalphaMS/P4MS compositions exhibit two coexisting aPS/PalphaMS and aPS/P4MS phases in the immiscibility loop. In the immiscible loop, SEM measurements revealed evidence in contrasting with DSC for criteria of miscibility. DSC characterization revealed a single T, for most ternary blend compositions; however, SEM graphs apparently indicated sub-micron phase domains, except for several PalphaMS-rich compositions (> 80%). The T-1(H) and T-1rho(H) techniques using NMR were found to resolve the dilemma between the conventional thermal analysis and microscopy results, and indeed supported that the ternary blends at above 80% Pg.MS are completely homogeneous on the molecular level. Attempts have been made to resolve the seemingly contradictory interpretations on the complex ternary phase structures and domains from the DSC, and microscopy results. (C) 2004 Elsevier Ltd. All rights reserved.