Thermal concentration fluctuation in the blends of deuterated poly(ethylene oxide) (dPEO) and poly(vinyl acetate-co-vinyl alcohol) [P(VAc-VOH)] with various VOH contents f OH were examined by small angle neutron scattering techniques at a fixed blend composition, dPEO/P(VAc-VOH) ¼ 20/80 which is close to the critical composition. Blends at the highest f OH (¼0.35) showed a non-Lorentzian scattering profile: specifically the scattering intensities at the low q (angle) region were suppressed compared to those expected from the random phase approximation (RPA) theory. However, for the blends at lower f OH ( 0.28), the profiles could be represented by the RPA. Using the RPA we determined effective values of the Flory-Huggins interaction parameter v eff as a function of f OH (¼0-0.28). The v eff showed the minimum around f OH ¼ 0.1-0.18 meaning the highest miscibility of the blend at these f OH . On the basis of the random copolymer theory, we evaluated the three interaction parameters v Ac-EO , v EO-OH , and v Ac-OH separately from the v eff (f OH ) and found the order of magnitude; v Ac-EO \ 0 \ v EO-OH \ v Ac-OH . The largest positive v Ac-OH showing intrachain interaction in the P(VAc-VOH) copolymer was concluded to be the origin of the enhanced miscibility at around f OH ¼ 0.1-0.18. On the basis of the Coleman and Painter's theory, the effects of hydrogen bonding on these three v A-B were discussed.
Viscoelastic terminal relaxation behavior of unentangled polymers having hydrogen bonding moieties was examined. Specifically, partially saponified poly(vinyl acetate), i.e., poly(vinyl acetate-co-vinyl alcohol) with various hydroxyl (OH) group contents, f OH , was used as a model polymer. Formation of hydrogen bonds due to the presence of the OH groups resulted in the increase of both the glass transition temperature, T g , and the terminal relaxation time, τ w. For the viscoelastic spectra of all the samples, time-temperature superposition principle approximately held. The shift factors could be expressed by the universal Williams Landel Ferry equation by setting appropriate reference temperatures, T r *. Comparison of τ w under an iso-frictional condition (at T r *) revealed the formation of aggregates of constituent polymers. By considering the distribution of the aggregation numbers predicted by the mean field percolation model the viscoelastic spectra could be reproduced when f OH ≤ 0.28. However, for the samples with f OH = 0.35 and 0.37, an extra relaxation component was found to exist in addition to the prediction of the percolation model.
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