Embedding medical scrubs with robust biocidal functions could potentially reduce pathogen cross-contamination and healthcare-associated infections. Here, a halamine precursor monomer, 1-acryloyl-2,2,5,5-tetramethylimidazolidin-4-one (ACTMIO), was covalently grafted to a poly(ethylene terephthalate) (PET) fabric, which is a common textile material used in medical scrubs, via a controlled free radical graft polymerization reaction using a "paddry-cure" finishing process. Based on a computational model and Hansen solubility theory, an ideal free radical reaction system was designed and implemented. The obtained ACTMIOgrafted (H-PET-g-ACTMIO) fabrics exhibited high grafting ratios of the monomers, desired properties of improved hydrophilicity, large active chlorine capacity, promising chlorine rechargeability, and desirable washing durability due to the robust covalent bonds between halamine moieties and PET fabrics. The chlorinated H-PET-g-ACTMIO fabric demonstrated powerful and regenerable biocidal performance against pathogenic bacteria, revealing the great application potential as a bioprotective medical textile. In addition, the successful application of Hansen solubility theory in surface modification of chemically inert polyester fibers provides a good example of controlling free radical polymerization reactions on textile materials.