Carbon-13 T-1 rho investigation in two polycarbodiimides

The molecular motions of carbons in two polycarbodiimides were studied by C-13 cross-polarization, magic angle spinning nuclear magnetic resonance. From these results, the C-13 spin-lattice relaxation times in the rotating frame were measured. In this paper we discuss the molecular motions for each carbon of the two polycarbodiimides. The main-chain carbon of polycarbodiimide (I) with methyl has higher activation energy, 23.12 kJ/mol, than that of polycarbodiimide (II) with the methoxy side chain, 10.47 kJ/mol. From these results, we surmise that polycarbodiimide (I) has a bigger steric interaction with the main-chain carbon since the methyl group is located in the meta-position of the aromatic ring. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.