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Polydimethylsiloxane (PDS) and it mixtures with styrene and polystyrene (PSt) are able to form stable monolayers at the liquid‐gas interfaces in contrast to pure styrene or PSt. The surface pressure — molecular area isotherms of PDS monolayers have two regions at low and high pressures with pronounced transition plateau in between. The area per PDS molecule in the liquid‐expanded state is about 1.60 nm2 (at 5 mN/m) that can be explained by twisting of polymer chain into the helical conformation. The area per PDS molecule in the liquid‐condensed state is about 0.48 nm2 (at 20 mN/m) that can be explained by PDS reorientation in the helical conformation from the horizontal to the vertical position with respect to the air‐water interface. The addition of styrene in the PDS monolayer drastically changes the π‐A isotherms (no transition plateau) with area increase from 0.47 till 2.70 nm2 per PDS with the increasing of polymer concentration from 1 to 10 mass %. In contrast, there are only small quantitative changes in the isotherms in the presence of PSt in the PDS monolayer. Thus, the formation of the polymer adsorption layers at the interface has been studied, modeling the initial and final step of the styrene polymerization in emulsion.

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