Arrhenius plot of the different relaxation processes in a-PEMA from the literature. 7,18,19 Below the glass transition temperature T g the ß-process is already present, whereas the α-relaxation starts above T g. Both merge at a certain temperature and form the a-relaxation. At higher temperatures the segmental isotropization is clearly separated from the a-relaxation, while at lower temperatures it is very similar to the α-process.
Different motions of the carboxyl group of PEMA reflected in 13C NMR line shapes. (a) In the glassy state slow 180° flips of the carboxyl group occur being too slow to preaverage the static 13C CSA tensor. 20 (b) Above Tg in the cold melt the line shape changes dramatically and shows an axial averaged tensor. 7 This averaging is caused by rotational fluctuations about the local chain axis. (c) At higher temperatures in the warm melt the isotropization process leads to an isotropic 13C NMR line through isotropic jumps of short chain sequences with 5–10 repeat units. 7,10
On the left the static 13C NMR spectra of the carboxyl carbon of a-PEMA are plotted for different temperatures. On the right the corresponding EXPRESS simulations with two jump rates are shown fitting the experiments very well.
Arrhenius plots of the two simulated processes of (a) labeled a-PEMA (blue) and (b) a mixture of labeled a-PEMA and an unlabeled PEMA brush (green). The isotropization process (X) can be fitted by a WLF function (solid lines), whereas the anisotropic rotation (O) can be described by an Arrhenius function (dashed lines).
Arrhenius plots of the two simulated processes of (a) brush A labeled at the particle surface (magenta), (b) brush B labeled in the middle of the brush shell (orange), and (c) brush C labeled at the chain ends (red).
The core sizes and shell thicknesses obtained by dynamic light scattering. The starred (*) numbers indicate labeled regions of the grafted PEMA chains. Brush A is labeled at the core surface, brush B in the middle of the chains, and brush C at the chain ends.
Fit parameters for the WLF functions and Tg of PEMA from DSC for the different samples.
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