Abstract
^13^C and ^1^H relaxation times were measured as a function of temperature in two magnetic fields for dilute solutions of phenolphthalein poly(ether sulfone) (PESβC) in deuterated chloroform. The spinβlattice relaxation times were interpreted in terms of segmental motion characterized by the sharp cutoff model of Jones and Stockmayer (J. S. model). The phenyl group rotation is treated as a stochastic diffusion by the J. S. model. The restricted butterfly motion of the phenyl group attached to the cardo ring in PESβC is mentioned but is not discussed in detail in this work. Correlation times for the segmental motion are in the picosecond range which indicates the high flexibility of PESβC chains. The correlation time for the phenyl group internal rotation is similar to that of the segmental motion. The temperature dependence of these motions is weak. The apparent activation energy of the motions considered is less than 10kJ/mol. The simulating results for PES are also reasonable considering the differences in structure compared with PESβC. The correlation times and the apparent activation energy obtained using the J. S. model for the main chain motion of PESβC are the same as those obtained using the damped orientational diffusion model and the conformational jump model.