Carbon-13 T1ρ investigation in two polycarbodiimides

The molecular motions of carbons in two polycarbodiimides were studied by 13C cross-polarization, magic angle spinning nuclear magnetic resonance. From these results, the 13C 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.