Aggregation behavior of the organic-soluble semi-aromatic polyimides, whose degrees of imidization range from 69 to 96%, obtained using 4,4'-oxydianiline, 4,4'-diamino-3,3'dihydroxybiphenyl, and bicyclo[2.2.2]-oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BCDA) in N-methylpyrrolidone (NMP), NMP/cyclohexanone, and NMP/?-butyrolactone (BCDA-based polyimides) were studied by static light scattering (SLS) and dynamic light scattering (DLS). The DLS analyses for the multirelaxation modes demonstrated the specific character unlike flexible polymers that the single BCDA-based polyimide chains first associate with each other to form small clusters in the dilute region, and then expand to large aggregates by the entanglements between the small clusters with an increasing concentration into the semi-dilute region. Given the semi-aromatic structure of BCDA-based polyimides weakening the charge transfer (CT) interaction between the diamine and the dianhydride unit, it is concluded that the unique aggregation behavior of BCDA-based polyimides is dominated by the balance between the driving force for the organic solubility given by both the increase in bulkiness and the decrease in the CT interaction, and that for the organic insolubility derived from both the hydrogen-bonded interaction of the phenolic hydroxyl groups and the pp interaction of the phenyl rings. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012