Three halogen-free, phosphorus-based flame retardant monomers were synthesized with good yields and characterized using FT-IR, H-1 NMR, and P-31 NMR. Two of the monomers were novel phosphoramides and the third was derived from cyclotriphosphazene. Each monomer was coated onto cotton substrates with the aid of a UV flood curing system. The impacts of monomer concentration, photoinitiator concentration, UV exposure time and proximity of the specimen to the UV lamp on coating yield were evaluated by experiments designed with JMP Pro 10. Of the three monomers, the cyclotriphosphazene derivative was polymerized into a coating that was durable to Soxhlet extraction with acetone. Vertical burn testing showed that all three monomers are valuable flame retardants. These results agreed with thermogravimetric analysis findings that demonstrated quantitatively the effectiveness of each monomer at promoting char formation. For the cyclotriphosphazene derivative, the coating was easily visualized covering significant portions of the fabric using scanning electron microscopy.