10.1021/la0351461.s001 L. Hamon L. Hamon Y. Grohens Y. Grohens Y. Holl Y. Holl Thickness Dependence of the Glass Transition Temperature in Thin Films of Partially Miscible Polymer Blends American Chemical Society 2003 Glass Transition Temperature poly PMMA film conformation energy Δ E glass transition temperature Partially Miscible Polymer Blends modification miscibility bulk stereoregular T g PEO blend 2003-11-25 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Thickness_Dependence_of_the_Glass_Transition_Temperature_in_Thin_Films_of_Partially_Miscible_Polymer_Blends/3358975 The thickness dependence of the glass transition temperature, <i>T</i><sub>g</sub>(<i>h</i>), has been investigated using ellipsometry at a variable temperature for thin films of partially miscible stereoregular poly(methyl methacrylate) (PMMA)−low-molecular-weight poly(ethylene oxide) (PEO) blends. These values were compared to <i>T</i><sub>g</sub>(h) values of pure stereoregular PMMA thin films, and the miscibility of PMMA/PEO systems is assessed by the so-called plasticizing effect of PEO, that is, Δ<i>T</i><sub>g</sub>*. In thin-film geometry, the miscibility of i-PMMA is enhanced compared with that in the bulk and becomes higher than that for s-PMMA in contrary to the bulk behavior of the blends. The conformation energy Δ<i>E</i> of the PMMA chains in the thin film increase much more for s-PMMA than for i-PMMA, indicating larger gauche to trans conformational rearrangement for the former isomer in the confined geometry. These large local modifications of the s-PMMA conformation in the thin film could result in modification of the mixing entropy and, therefore, be the main reason for the lower miscibility of PEO in s-PMMA as compared to that in i-PMMA.