A poly(oxyalkylene) polymer and a metal salt of a carboxylic acid, sulfonic acid, or alkylsulfate, in combination are useful as a polymer processing additive synergist. Polymer processing additive compositions, homogeneously catalyzed olefin compositions, and other extrudable polymer 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.