An effect of stereoregularity on the structure of poly(methyl methacrylate) at air and water interfaces

We here show the interfacial conformation of isotactic poly(methyl methacrylate) (i-PMMA) in films as revealed by sum-frequency generation vibrational spectroscopy, which possesses the best depth resolution among available techniques, and discuss an effect of stereoregularity on the interfacial structure of PMMA. At the air interface, i-PMMA takes the trans-gauche backbone conformation with some degree of main chain distortion and/or of trans-trans conformation. This may lead to a helical conformation of i-PMMA chains where the hydrophilic carbonyl groups, as well as hydrophobic methylene, alpha-methyl, and ester methyl groups, are oriented towards the outermost region of the i-PMMA film. Thus, even though i-PMMA chains come in contact with water, the chain conformation at the interface was little changed. These structural details of i-PMMA at the air and the water interfaces are significantly different from those observed for s-PMMA.