C-13 NMR INVESTIGATION OF THE LOCAL DYNAMICS OF ARYL-ALIPHATIC POLYESTERS IN SOLUTION

The local motions of aryl-aliphatic polyesters based on ethylene glyco l and hydroxybenzoic acid or isophthalic acid were investigated in chl oroform and trifluoroacetic acid/dichloromethane solutions using C-13 n.m.r. Measurements of the C-13 spin-lattice relaxation times have ind icated the existence of hydrogen-bonding interactions between the carb oxyl groups of the polymers and the solvent in the trifluoroacetic aci d/dichloromethane mixture. Interpretation of the C-13 spin-lattice rel axation times in terms of segmental main-chain motions was carried out using the Dejean-Laupretre-Monnerie orientation autocorrelation funct ion. The internal motions of the aromatic rings have been described in terms of jumps between two equilibrium positions for the hydroxybenzo ic rings and by stochastic jump processes for the isophthalic rings. T he energy barriers determined for these motions have been compared wit h those measured in related systems or estimated from conformational e nergy calculations.