Disclosed are new compositions consisting of branched polyphosphonates and specific additive compositions that exhibit superior resistance to degradation due to exposure to air, high temperature, moisture or combinations thereof. Also disclosed are polymer mixtures or blends comprising these branched polyphosphonates/additive compositions and commodity and engineering plastics and articles produced therefrom. Further disclosed are articles of manufacture produced from these materials, such as fibers, films, coated substrates, moldings, foams, fiber-reinforced articles, or any combination thereof.