Rotating frame proton spin‐lattice relaxation measurements of poly(ethylene oxides)

Measurements of T 1ρ as a function of temperature have been made on three polyethylene oxides (PEO) with molecular weights of 550, 6000, and 2.8 × 10 6 in order to try to elucidate various problems arising in the interpretation of previous T 1 measurements on PEO. In contrast to the T 1 measurements, the T 1ρ measurements show discontinuities at the melting or softening points of the respective polymers concerned, and also show nonexponential magnetization decay in the case of PEO 6000 and 2.8 × 10 6 , which is presumbly due to the existence of “mobile” and “crystalline” regions, in qualitative agreement with NMR studies and x‐ray measurements. Motional correlation frequencies and activation energies have been derived where possible by using the BPP theory adapted to the rotating frame and also the strong collision Slichter‐Ailion theory. There is reasonable correlation with other data on motional frequencies where it is available, although the overall situation for the so‐called α transition in PEO 6000 and 2.8 × 10 6 is still not clear. It is suggested that spin‐diffusion is an important mechanism for all three polymers; for PEO 550 because it contains CH 3 endgroups which act as sinks, and for the other two polymers where the mobile fraction performs the same function.