We report a strategy for the preparation of semitelechelic polymers containing two distinct functionalities at one chain end by consecutive and chemoselective nucleophilic aromatic substitution reactions on 2,4,6-trichloro-1,3,5-triazine (TCT). Because of its commercial availability, well-defined nature, and ubiquity in biological applications, monomethyl ether poly(ethylene glycol) (mPEG) was chosen to demonstrate the utility of this ω,ω-heterodifunctional end-group modification strategy. TCT-functionalized mPEG underwent highly efficient ω,ω-heterodisubstitution via sequential chemoselective substitution with model thiols and amines. The efficiency of nucleophile conjugation to the polymer end group was confirmed by 1H NMR spectroscopy and matrix assisted laser desorption-ionization time-of-flight mass spectrometry. In addition, density functional theory calculations provided insight into the importance of nucleophile addition order. This route introduces TCT derivatization as a powerful and facile tool to achieve specific polymeric end-group complexity and efficient heterogeneous functionalization.