A series of hyperbranched poly(arylene ether phosphine oxide)s (HB PAEPOs) were prepared via an A(2) + B-3 polymerization scheme with tris(4-fluorophenyl)phosphine oxide as B-3, and a variety of bisphenols as A(2). The effects of the reactivity of the A, monomer, the A:B ratio, the addition mode, the solvent, and the concentration on the final molecular weight, polydispersity index (PDI), and degree of branching (DB) were studied. Soluble HB PAEPOs with weight-average molecular weights of up to 299,000 Da were achieved. Reactions in which the A2 component was added slowly resulted in lower DBs (0.2-0.5), whereas the slow addition of the B, component provided samples with DBs of approximately 0.75. Reactions performed under high-dilution conditions afforded completely soluble materials with weight-average molecular weights of 9000-12,100 Da and PDI values as low as 2.20. The molecular weights achieved under high-dilution conditions were independent of the mode of monomer addition. (C) 2003 Wiley Periodicals, Inc.