Polymer blends, in particular polyphenylene ether-polyamide blends, are effectively compatibilized by incorporating under blending conditions certain oligomers, cooligomers, polymers and copolymers of narrow molecular weight distribution that are prepared under free radical polymerization conditions with glycidyl-functionalized nitroxyl initiators. The oligomers, cooligomers, polymers and copolymers contain at least one oxyamine group and at least one glycidyl-containing initiator group. The polymer blends have excellent mechanical properties.