The coupling of the a and 8 processes in poly(ethyl methacrylate) has been investigated in detail by multidimensional 13C solid-state NMR of the carboxyl moiety. In the glassy state the underlying molecular motion is anisotropic and involves a it flip of the side group coupled to a rocking motion around the local chain axis with a ±20°a mplitude. Above the glass transition (Tg) the molecular motion remains highly anisotropic. The geometry of the molecular motion is similar to that in the glass; however, the rocking amplitude increases upon raising the temperature above Tt. This is indicative of a pronounced influence of the a main-chain motion on the 8 side-group motion which manifests itself by a marked increase of the rocking amplitude to a value of ±50°at 365 K (Tg+ 27 K). It eventually leads to a locally anisotropic uniaxial chain motion at 395 K (Tg + 57 K). This behavior differs significantly from that of other amorphous polymers above T( where the molecular motions of both the main chainandside groups are isotropic. The averaged correlation times extracted from NMR experiments are in good agreement with data from dielectric relaxation.
Cellulose as well as two cellulose/poly(vinyl alcohol) blends with compositions 60/40 and 80/20 w/w exposed to water are investigated by 1H-, 2H-, and 13C solid-state NMR spectroscopy. For pure cellulose, the lower temperature, secondary dielectric relaxation process can be attributed to the onset of motion of adsorbed water molecules as revealed by 2H-NMR spectroscopy. This water is not crystalline below 270 K. Three distinct kinds of water bound to the polymer matrix are detected, as far as dynamic behavior is concerned. First there is nonfreezable, strongly bound water that is rigid but amorphous at low temperatures. The second component is highly mobile and exhibits isotropic motion even below 270 K. Interestingly, there is a third component of water molecules that undergo well-defined 180° flips around their bisector axis with a rate greater than 105 s-1 due to anisotropic constraints. In contrast to the first two kinds, this component cannot be removed from the polymer matrix by drying even at elevated temperatures and its motional process is observed over the whole temperature range, investigated from 190 to 370 K. All three kinds of matrix water coexist in a wide temperature range. In the blends, 2D 1H−13C heteronuclear wide line separation (WISE) NMR spectroscopy shows that at our low concentrations the water is predominantly associated with the cellulose backbone. No water can be detected in the immediate vicinity of the poly(vinyl alcohol). Applying spin diffusion, we detected nanoheterogeneities in the range of about 3 nm within these systems.
Heating an amorphous polymer above its glass transition yields an isotropic melt.1 Exceptions are liquid crystalline polymers with mesogenic groups2 or semicrystalline polymers that exhibit conformationally disordered mesophases.3 In such mesophases the chain dynamics are
I3C-CP/h4AS-NMR (cross-polarization magic angle spinning), 2D-WISE (wideline separation experiment) and 'H-spin diffusion experiments allow to gain new insight into the structure and dynamics of solid polyelectrolyte-surfactant complexes, a material with pronounced mesophase formation. Experiments were performed on two different complexes of polystyrene sulfonate and octadecyltrimethylammonium or tetradecyltrimethylammonium counterions, PSS-C18 and PSS-C14. The strong mobility differences between the ionic and alkyl phase in the lamellar complex PSS-C18 are reflected in the NMR behavior: in the surfactant tails, a mobility gradient towards the terminal methyl group is observed. This fact as well as a high content of gauche conformations suggest a noninterdigitating morphology of the tails at room temperature. The behavior changes during cooling below an endothermic transition centered at 255 K where a high trans content and a homogenization of the side chain dynamics is observed. We attribute this transition which is invisible in the X-ray experiments to the formation of a highly transoid, interdigitated phase of the surfactant tails which is however not crystallized in a classical sense. 'H-spin diffusion experiments allow to estimate the distance between mobile and immobile regions of the sample. For the complex PSS-C14, the length scale determined by NMR is essentially that of the primary lamellar structure. For PSS-C18, a characteristic length of the density fluctuations within the proposed undulated lamellar structure is estimated.
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