Monolayer Behavior of Some Stereoregular Poly(methacrylates)

The monolayer behavior of some poly(methacrylates) with short ester side chains (methyl, ethyl, and isobutyl) is studied as a function of the tacticity. In all cases, the isotactic polymers are observed to form expanded monolayers, whereas the syndiotactic materials yield more condensed monolayers. These observations are attributed to differences in the lateral cohesive interactions of the segments in the monolayer, which again can be correlated with the difference in spatial orientation of the ester groups with respect to the backbone and the air-water interface. The anomalous temperature dependence of the isotactic polymers (a contraction of the monolayers at higher temperatures) can be interpreted in terms of an enhancement of these lateral cohesive interactions (a decrease of the solvent quality of the environment). Surface potential measurements yield results which appear to be in agreement with the interpretation of the monolayer isotherm data and also illustrate the monolayer crystallization process proposed for isotactic PMMA in a previous publication. Isotactic poly(methacrylic acid) is observed to form stable monolayers on a pure water subphase, in contrast to syndiotactic poly(methacrylic acid).