A poly(oxyalkylene) polymer having a weight average molecular weight of at least 50,000 grams per mole and a metal salt of a carboxylic acid, sulfonic acid, or alkylsulfate, in combination are useful as a polymer processing additive. In some embodiments, the polymer processing additive further includes a poly(oxyalkylene) polymer having a weight average molecular weight of up to 20,000 grams per mole Polymer processing additive compositions and thermoplastic, for example, polyolefin, compositions including a poly(oxyalkylene) polymer and a metal salt of a carboxylic acid, sulfonic acid, or alkylsulfate are disclosed. Methods of reducing melt defects during the extrusion of a thermoplastic polymer, which may be a homogeneously catalyzed polyolefin, are also disclosed.