Segmental motions of spin-labelled poly(ethylene oxide) in dilute solution

The rotational correlation times (τ) of spin-labelled poly(ethylene oxide), (M_w=20 000) were measured in benzene, pyridine and water. It was found that τ is independent of polymer concentration (c) when c<0,15 g/(ml solvent). In dilute solutions τ values of 49 ps, 43 ps and 100 ps in benzene, pyridine and water at 293 K were obtained. A comparison with results of dielectric relaxation and nuclear magnetic resonance measurements indicated that τ_diel. < τ¹³_CNMR < τ_{spin-labelling} < τ¹_{H NMR}. Values 17.7±2,2 kJ/mol and 17,3kJ/mol for the potential barrier of local conformational changes of PEO in pyridine and water solutions were obtained. The apparent hydrodynamic radii (0,35–0,46 nm) indicated the loosely arranged random coil state of the polymer molecules in solution at 293 K.