CHAIN FLEXIBILITY AND P-31 NMR SPIN-LATTICE RELAXATION MEASUREMENTS ON MELTS OF HALOGENATED POLY(THIONYLPHOSPHAZENES)

The chain flexibility of halogenated poly(thionylphosphazenes) (PTPs) [(NSOX) (NPCl2)(2)](n) (X = F, Cl) was investigated by measuring the P -31 spin-lattice relaxation times of PTP melts. T-1 times were obtaine d at two different magnetic fields and at various temperatures above t he glass transition of the polymers. The minimal T-1 time occurred at lower temperatures for the fluorinated polymer than for the chlorinate d polymer. This result is in agreement with trends in glass transition temperatures of these polymers and with ab initio molecular orbital c alculations on the chain flexibility of model compounds of these polym ers. The Hall-Helfand model for the dynamics of polymer chains was use d to fit the experimental T-1(T) curves. This model describes the moti ons of the polymer chains that lead to the longitudinal relaxation as correlated conformational jumps. T-1 measurements at two different fie ld strengths indicated that chemical shift anisotropy contributes sign ificantly to the spin-lattice relaxation.