Glass transition phenomena observed in stereoregular PMMAs using molecular modeling

The way surface interactions could affect thermal behavior of a polymer is of relevant importance in the polymer-nanocomposite studies. A complete description of such microscopic interactions is not yet reached. To give a better understanding of such a behavior poly(methyl methacrylate), PMMA, offers a particular regard since according to the tacticity of its chain, different physical properties are exhibited. Among the properties of interest is the glass transition temperature, Tg whose difference between the two configurations is more than 60 degrees. This difference tends to cancel out as the thickness of the PMMA film on a specific substrate decreases. Accordingly the Tg of the isotactic chain, i-PMMA increases while that of the syndiotactic chain, s-PMMA, decreases. Different attempts have been carried out to explain this different behavior. In this article, results stemming from molecular simulations in the bulk are reviewed, and used to give possible explanation of both behaviors.