Small‐angle neutron scattering study on the miscibility and concentration fluctuation of hydrogen‐bonded polymer blends

<jats:title>Abstract</jats:title><jats:p>Thermal concentration fluctuation in the blends of deuterated poly(ethylene oxide) (dPEO) and poly(vinyl acetate‐<jats:italic>co</jats:italic>‐vinyl alcohol) [P(VAc‐VOH)] with various VOH contents <jats:italic>f</jats:italic><jats:sub>OH</jats:sub> were examined by small angle neutron scattering techniques at a fixed blend composition, dPEO/P(VAc‐VOH) = 20/80 which is close to the critical composition. Blends at the highest <jats:italic>f</jats:italic><jats:sub>OH</jats:sub> (=0.35) showed a non‐Lorentzian scattering profile: specifically the scattering intensities at the low <jats:italic>q</jats:italic> (angle) region were suppressed compared to those expected from the random phase approximation (RPA) theory. However, for the blends at lower <jats:italic>f</jats:italic><jats:sub>OH</jats:sub> (≤0.28), the profiles could be represented by the RPA. Using the RPA we determined effective values of the Flory‐Huggins interaction parameter χ<jats:sub>eff</jats:sub> as a function of <jats:italic>f</jats:italic><jats:sub>OH</jats:sub> (=0–0.28). The χ<jats:sub>eff</jats:sub> showed the minimum around <jats:italic>f</jats:italic><jats:sub>OH</jats:sub> = 0.1–0.18 meaning the highest miscibility of the blend at these <jats:italic>f</jats:italic><jats:sub>OH</jats:sub>. On the basis of the random copolymer theory, we evaluated the three interaction parameters χ<jats:sub>Ac–EO</jats:sub>, χ<jats:sub>EO–OH</jats:sub>, and χ<jats:sub>Ac–OH</jats:sub> separately from the χ<jats:sub>eff</jats:sub>(<jats:italic>f</jats:italic><jats:sub>OH</jats:sub>) and found the order of magnitude; χ<jats:sub>Ac–EO</jats:sub> < 0 < χ<jats:sub>EO–OH</jats:sub> < χ<jats:sub>Ac–OH</jats:sub>. The largest positive χ<jats:sub>Ac–OH</jats:sub> showing intrachain interaction in the P(VAc‐VOH) copolymer was concluded to be the origin of the enhanced miscibility at around <jats:italic>f</jats:italic><jats:sub>OH</jats:sub> = 0.1–0.18. On the basis of the Coleman and Painter's theory, the effects of hydrogen bonding on these three χ<jats:sub>A</jats:sub><jats:sub>‐</jats:sub><jats:sub>B</jats:sub> were discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2556–2565, 2008</jats:p>