Disclosed are branched polyphosphonates produced using a polycondensation process, that result in polyphosphonates having a Tg of at least 100° C., and which can be further processed to have improved hydrolytic stability compared to other polyphosphonates. The method and polyphosphonate compositions may be made from readily available starting materials providing lower cost fire retardant materials. Also disclosed are polymer compositions that comprise these branched polyphosphonates and at least one other polymer, wherein the resulting polymer compositions exhibit flame retardant properties.