Monolayer and thin film behaviour of stereoregular poly(methacrylates)

In search of an alternative stereocomplexing system, monolayers of mixtures of isotactic PMMA and syndiotactic poly (isobutylmethacrylate) (s-PiBMA) were studied. An anomalous transition observed in the isotherms of these mixtures was shown nor to correspond to a stereocomplexation process, but rather to a pressure induced mixing, which is responsible for a suppression of the crystallization of the i-PMMA component in the monolayer. Miscibility is also observed (even without a required surface pressure build up) for mixtures of s-PiBMA and s-PMMA. The large effects observed indicate that mixing must occur up to close to the segmental level. The locally parallel alignment of the chains, which is more or less imposed on the system by its twodimensional character, appears to be favourable with respect to the adhesive interactions, as illustrated by the fact that random copolymers exhibit smaller deviations than homopolymer mixtures. In the case of the mixtures of s-PiBMA and i-PMMA, clear molecular weight effects are found, both with respect to the kinetics of the lateral interdiffusion process upon mixing as well as in terms of the thermodynamics of the mixing process.