Depletion Effect on Self-Organization of atactic Polymer Chain Segments in Microcells*

Glass transitions for atactic polystyrene and poly(methyl methacrylate) prepared in nano-cells by microemulsion polymerization in the presence of non-solvents were measured by DSC experiments. An increase in $T_{g }$was observed for these polymers. The first DSC scan for the virgin polymers indicated $T_{g}$ at 112 $^{o}$C and 138 $^{o}$C for$ a$-PS and $a$-PMMA, respectively. While the re-precipitated samples show $T_{g}$ at 105 $^{o}$C and 125 $^{o}$C, respectively. Solid-state NMR relaxation and wide angle X-ray diffraction experiments indicated that the virgin polymer powders were in compact and partially self-organized states. The re-precipitated $a$-PS and $a$-PMMA did not show any self-organization under the same experimental conditions, although there are no changes in molecular weight or tacticity of the polymer chains. A depletion-interaction phenomenon was understood to provide entropic force for the self-organization of polymer chains inside the walls of the microemulsion cells during polymerization.