Bis(halophthalimides) such as, 3-bis[N-(4-chlorophthalimido)]benzene are prepared in slurry in an organic liquid such as o-dichlorobenzene or anisole, by a reaction at a temperature of at least 150°C between at least one diamino compound, preferably an aromatic diamine such as m- or p-phenylenediamine, and at least one halophthalic anhydride such as 4-chlorophthalic anhydride, in the presence of an imidization catalyst such as sodium phenylphosphinate. The solids content of the reaction mixture is at least about 5% and preferably at least about 12% by weight. The product slurry may be employed directly in the preparation of polyetherimides, and similar slurries may be employed to prepare other polyether polymers.