Melt Dynamics of Blended Poly(oxyethylene) Chains and Rings

Monodisperse cyclic poly(oxyethylene) (CPOE) was synthesized from linear dihydroxy-terminated poly(oxyethylene) (LPOE) with molecular weights from 400 to 1500 g/mol. Blends of CPOE with LPOE were prepared and examined with pulsed-field-gradient (PFG) H-1 NMR and rheology to determine the self-diffusion coefficient (D) and zero-shear viscosity (eta) in the melt. Single average diffusion coefficients were measured for all blends. For blends prepared from components with equivalent molecular weights >400 g/mol, the D's are suppressed and the eta's are enhanced in comparison with predictions based on binary mixing rules. This is attributed to topological threading of rings onto linear chains. Blends of perdeuterated LPOE with hydrogenous CPOE (1500 g/mol) were prepared and examined with PFG NMR. The resulting D's, representing only the CPOE in the blends, are smaller than the average D's measured for the fully hydrogenous blends at a given composition, indicating that complete averaging of the component molecular dynamics does not occur in these binary blends. Extrapolation to zero CPOE concentration yielded the trace D for 1500 g/mol CPOE in LPOE (2.8 x 10(-12) m(2)/S at 56 degrees C). This trace D, assumed characteristic of threaded conformations, was used with the pure-component D's and a three-term mixing rule to determine the percentage of rings threaded as a function of CPOE concentration. The results are in qualitative and quantitative agreement with published modeling Studies.