We synthesized graft copolymers comprising a poly(ethenesulfonate) (PES) backbone with oligo ethylene glycol or oligo perfluoropolyether side-chains for the first time. The effect of fluorination on the polymerization of oligo ethylene glycol ethenesulfonate (EGES) monomers, containing one (EG1ES) or three (EG3ES) ethylene glycol units, was studied. In a conventional free radical polymerization, EGES monomers formed only oligomers. In contrast, the fluorinated oligo ethylene glycol ethenesulfonate (FEGES) monomers, containing two (FEG2ES) or three (FEG3ES) fluorinated ethylene glycol units, showed high conversions and high molecular weights. The reason for this drastic effect was the suppression of chain transfer reactions from methylene ether and methoxy groups, as we deduced from end-group analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF MS). This technique was not only used for a detailed end-group analysis, but also to determine the absolute molecular weight of PESs. Furthermore, we tested the reversible addition–fragmentation chain transfer (RAFT) polymerization of the FEGES monomers. Whereas the RAFT polymerization of FEG2ES was dominated by recombination processes, we achieved high end-group fidelity for PFEG3ES with an ethyldithiocarbonate chain transfer agent. PFEG2ES synthesized by RAFT was semi-crystalline, while PFEG3ES was fully amorphous at room temperature, as proved by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and wide-angle X-ray scattering (WAXS). Their low crystallinity, their adequate thermal stability and their reduced flammability due to the fluorination make PFEGES polymers potential materials as solid polymer electrolytes for battery applications.