One method of preparing a polyetherimide is by polymerization of an alkali metal salt of a dihydroxyaromatic compound (e.g., a disodium salt of bisphenol A (BPA-Na2)) with bis(halogenated phthalimide). The molecular weight of the resulting polyetherimide can be controlled in two ways. The first is to use a molar excess of bis(halogenated phthalimide) relative to the alkali metal salt of the dihydroxyaromatic compound. The second is to prepare bis(halogenated phthalic anhydride) in the presence of a monofunctional compound (e.g., phthalic anhydride) to form a capping agent. The phthalic anhydride is reacted with a portion of an organic diamine to form monohalogeno-bis(phthalimide). The monohalogenobis(phthalimide) is used as a capping agent in the polymerization reaction step by reacting with the phenol salt end groups in the growing polymer chain.
