The sodium salts of carboxylic acids and other weak acids are routinely used as nucleation agents for injection moldable poly(ethylene terephthalate) (PET) resins, One of the primary drawbacks accompanying their use is the degradation of the PET resulting from the attack of the ester by the sodium carboxylate. Several sodium carboxylates have been found based on pyrrole carboxylic acid that are effective as nucleants but which do not cause a reduction in the molecular weight of PET. In addition, tetraphenyl berate salts, although only marginally effective as nucleants, were observed to be efficient additives to PET for counteracting molecular weight loss caused by chemical nucleants.