To manufacture aromatic polyamide which is active layer in reverse osmosis composite membrane, interfacial polymerization using MPD(m-phenylene diamine) in water phase and TMC(trimesoyl chloride) in HCFC(1,1-dichloro-1-fluoroethane) organic solvent was researched. By using UV absorbance analysis method, thin film formation process was studied according to time. As a result, aqueous phase diffusion was dominant in the control of interfacial polymerization of early time, but when the concentration of monomers in organic phase was low(0.125wt%), organic phase diffusion controlled the reaction. In addition, interfacial reaction which proceeded with delayed time of early 20 seconds was completed within 60 seconds unstoichiometrically. Also concentration change on the interface was mathmatically perdicted and the thickness of thin film was calculated by using this result. The calculated value of thickness of thin film provides good consistence with experimental results. Also theoretical equation of thickness in thin film is as follows.
δ=∫_t1^t2N₁ʝ₁dt + ∫_t1^t2N₂ʝ₂dt