When mixtures of isotactic and syndiotactic PMMA are spread on the air water interface from a non-complexing solvent, a pressure induced transition can be observed, that is identified as a stereocomplexation between the two stereoregular components in the mixture, similar to bulk or solution processes. Analogous to the monolayer crystallization of isotactic PMMA, double helical structures are formed that can be transferred to solid substrates forming oriented thin films.