Spin Relaxation and Dynamics of Ring Poly(ethylene oxide) in Melts

The spin relaxation of protons and deuterons was investigated in melts of ring poly(ethylene oxide) (PEO) macromolecules with a molecular mass varying from 5280 to 96,000 Da. Comparison of the frequency dispersion of NMR spin–lattice relaxation rates with corresponding rates in the melts of linear PEO of similar molecular masses shows that there is a significant mutual interpenetration of neighboring ring macromolecules, although less pronounced than in their linear counterparts. The mean-squared displacement of ring segments in the investigated frequency interval corresponding to the time interval 8 × 10–9 to 2 × 10–5 s depends on time as ⟨rn2(t)⟩ ∝ t0.39, in agreement with neutron spin echo (NSE) results. Decays of the normalized Hahn echo signal in ring macromolecules are exponential within experimental errors, unlike for their linear counterparts where strongly nonexponential behavior is found. This indicates the absence of dynamic heterogeneity of ring segments seen by NMR and associated with the presence of end segments in their linear analogues.