Effect of Cross-Links on the Miscibility of a Deuterated Polybutadiene and Protonated Polybutadiene Blend

The effect of peroxide cross-linking on the phase diagram and the scattering function for a critical mixture of perdeuterated polybutadiene (DPB) and protonated polybutadiene (HPB) has been examined by small-angle neutron scattering as a function of temperature. The scattering curves for the cross-linked blends were essentially temperature independent. It was found that even at temperatures (T) below the critical temperature (T_c) of the un-cross-linked (linear) blend (e.g., T = 0 °C; T_c = 99.2 °C), the cross-linked blends remained single phase and did not undergo microphase separation. The calculation of the reduced temperature, ϵ, for the cross-linked blends also implied that the cross-linking greatly increased the single-phase region of the phase diagram. A comparison of the scattering for the cross-linked blend with that of the linear blend at the cross-linking temperature (150 °C) showed a suppression in the scattering due to the presence of the cross-links. However, it was experimentally found that the concentration fluctuations present at the temperature of cross-linking dominate the scattering, which made it rather difficult to verify the prediction on the scattering function made by de Gennes.