SELECTIVE EXCITATION SASS C-13 NMR-STUDY OF THE PHENYLENE MOTION OF GLASSY-POLYMERS

Natural abundance C-13 chemical shift anisotropy (CSA) spectra of the aromatic CH carbons of bisphenol-A (BPA) residues were measured for BP A polycarbonate (BPAPC) and polyarylate (PAr) films at different tempe ratures by selective excitation switching angle sample spinning (SESAS S) NMR spectroscopy. The CSA spectra thus obtained were analysed in te rms of the two-site exchange model for the flip motion of the phenylen e group. In BPGPC, wide distributions in flip angle around 0 degrees a nd 180 degrees are well revealed under the situation of the first exch ange limit for the flip motion and the widths become significantly bro ader with increasing temperature, These results are in good agreement with those of the previous H-2 NMR analyses. Similar wide distribution s in flip angle are also recognized even at lower temperatures for PAr , which is a non-crystalline polymer composed of BPA and phthalic acid residues, suggesting more enhanced phenylene motion in this polymer. Moreover, the CSA spectra obtained for PAr above 60 degrees C are foun d not to be reproduced by using the simple two-site exchange model pri marily based on the flip motions around 0 degrees and 18 degrees'', pr obably owing to the onset of larger scale random motion of the flip ax is.