A CO2-philic antibacterial precursor was synthesized through hydrosilylation reaction of poly(methylhydrosiloxane) (PMHS) and tert-butyl acrylate in the presence of platinum-based catalyst. Carboxyl groups were then generated by hydrolyzing the precursor with trifluoroacetic acid to bond tert-butylamine molecules via amide bonds that were further chlorinated to N-halamines with tert-butyl hypochlorite. The resultant N-halamine polysiloxane was coated on cotton by adsorption from supercritical CO2 (scCO(2) ) to confer biocidal ability. This coating procedure provides an efficient way to attach antibacterial polymers onto substrates without using covalent bonds which limit the structure designs. Presented data showed that the antibacterial layer was stable toward washing and abrasion and provided potent biocidal activities against Staphylococcus aureus and Escherichia coli.