Based on measuring and analyzing the n-A isotherms and their differentiate curves for monolayer of poly-(styrene-maleic anhydride) (PSM) copolymer monolayer with different molecular weight, the formation and the effect of molecular weight on the phase transition of PSM monolayer were discussed in detail. The dynamic elasticity of each monolayer was determined by barrier oscillation method. It is shown that the interactions such as skew and twist of the macromolecular chains have great effect on the formation, the static and dynamic behavior of PSM monolayer. And the value of dynamic elasticity of the PSM monolayer is bigger in solid state than the one in liquid state. With increasing of molecular weight, the condensability, the rigidity, the stability and the dynamic elasticity of the PSM monolayer are all enhanced. With increasing of molecular weight, the phase transition of PSM monolayer becomes more complicated, the viscidity of the PSM monolayer is enhanced and the relaxation behavior of PSM monolayer becomes more obvious.

Key words: STYRENE, maleic anhydride, COPOLYMERS, MONOMOLECULAR FILMS, ELASTICITY, MOLECULAR WEIGHT, PHASE TRANSFORMATION