The dependence of Flory-Huggins interaction parameter x on temperature, composition, and chain length was investigated for binary blends of amorphous model polyolefins, materials which are structurally analogous to copolymers of ethylene and butene-1. The components were prepared by saturating the double bonds of nearly monodisperse polybutadienes (78 %, 88 %, and 97 % vinyl content) with H2 and D2, the latter to provide contrast for small-angle neutron scattering (SANS) experiments. Values of x were extracted from SANS data in the single-phase region for two series of blends, H97/D88 and H88/D78, using the randomphase approximation and the Flory-Huggins expression for free energy of mixing. These values were found to be insensitive to chain length (one test only) and to the component volume fractions for = 0.25, 0.50, and 0.75. Their temperature dependence (27-170 °C) obeys the form x(T) =A/T + B with coefficients that connote upper critical solution behavior, yielding Tc ~40 °C for one blend series (H97A/D88) and Tc ~60 °C for the other (H88/D78). These estimates are consistent with SANS pattern changes and supplemental light scattering results that indicate two-phase morphologies at lower temperatures. The x(D coefficients for the two series are also consistent with the random copolymer equation, although the interaction parameter obtained for branch C4-linear C4 chain units is much larger than that found by Crist and co-workers for saturated polybutadienes with lower ethyl branch contents.

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Photonic crystals fabricated from a diblock copolymer/homopolymer blend are reported. It is shown that large‐area, highly reflective, flexible films can be obtained in which the peak reflective wavelength can be tuned simply by altering the percentage of homopolymer in the blend. A fracture surface of a 40 % homopolymer blend is shown in the Figure.

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Energy-resolved, elastic neutron backscattering was employed to investigate the methyl group dynamics in polyisoprene between T = 2 K and room temperature. The use of partially deuterated samples (PI-d6, PI-d3, and PI-ds) and of a fully protonated sample (Pl-hg) allowed the separation of the dynamics arising from the methyl group and from the backbone. A two-step relaxation is observed and attributed to the methyl group rotation at low temperatures and to the main-chain relaxation close to the glass transition.An Arrhenius-like increase of the methyl group rotational correlation time r = ro exp(EtcJkT), with E^Jk = 1550 K ~12 kJ/mol and 0 ~1/ 0 = 23.5 meV (r0 ~1.76 X 10-13 s) describes well the midposition of the first elastic intensity decrease but not its breadth. A 3-fold jump model with a broad Gaussian distribution of activation energies (dE/E ~25%) around 1500 K can account for the observed temperature decrease. Inconstancies in the Q-dependence might be due to disorder effects. The torsional mode of the methyl group rotation is directly observed at = 23.5 meV by time-of-flight. Near the glass transition temperature a further decrease of the elastic scattering is observed due to the onset of a fast dynamics of the backbone in the picosecond range.