Disclosed are branched polyphosphonates produced via a superior transesterification process, and methods related thereto. These branched polyphosphonates exhibit a unique and advantageous combination of properties, such as outstanding fire resistance, improved heat stability, improved toughness, and superior processing characteristics. 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. Further disclosed are articles of manufacture produced from these polymers, such as fibers, films, coated substrates, moldings, foams, fiber-reinforced articles, or any combination thereof; these articles may be coated with a moisture barrier to enhance their moisture resistance properties.