In this work, a simple grafting method for the preparation of stable polymer layers on poly(ethylene terephthalate) was demonstrated. Poly(styrene-co-2-hydroxyethyl methacrylate) was synthesized by free radical polymerization. The copolymer was grafted onto poly(ethylene terephthalate) via the formation of ether linkages upon thermal annealing. The Grafting density of the copolymer was studied as a function of copolymer composition, PET surface treatment, annealing time, and annealing temperature. The stability of the grafted polymer layer on PET in organic solvent was improved compared to the non-grafted samples. In addition, poly(4-vinylpyridine-co-2-hydroxyethyl methacrylate) was grafted onto PET in order to show the versatility of this grafting method. Control experiments were carried out to demonstrate that the grafting occurs through the formation of an ether linkage with available hydroxyl groups on the surface. Based on these results, this grafting method offers a simple, versatile strategy for the preparation of stable polymeric layers on polymeric surfaces, and therefore, expands the tool box for functionalizing polymer/polymer interfaces.