Surface phosphonylation of thermoplastic polymers was previously demonstrated in both the liquid and gas phase. For the present study, the phosphonylation process was modified through the use of a two-chamber reactor and a dynamic oxygen flow in an effort to secure greater control of the gas phase reaction. Low-density polyethylene films were phosphonylated at both ambient and elevated temperatures for time periods ranging from 15 to 60 min. Subsequently, all films were analyzed by SEM, EDX, horizontal ATR-FTIR, surface roughness, and dynamic contact angle measurements. Analysis of the data indicates that after 15 min at ambient temperature, films do not phosphonylate to a degree that could be detected by the chosen methods. Phosphonylation was achieved at 30 and 60 min at ambient temperature, and at 60 min at 45 degrees C. The data indicate that optimal conditions for gas phase phosphonylation in the described apparatus are 25 degrees C for times greater than 15 min but less than 60 min.