Relationship between interchain spacing of amorphous polymers and blend miscibility as determined by wide‐angle X‐ray scattering

The average molecular interchain spacing (〈 R 〉) in Angstroms for amorphous polymers was calculated from the strong maximum in the wide‐angle X‐ray scattering (WAXS) diffraction scan using established equations. The half‐width ( HW ) of the maximum was used to qualitatively describe the distribution of 〈 R 〉. 〈 R 〉 and HW for immiscible blends corresponded to the weighted average of 〈 R 〉 and HW of the homopolymers in the blend. 〈 R 〉 for a miscible blend (natural rubber and high‐vinyl PBd) was much larger than the weighted average of 〈 R 〉 of the component homopolymers, indicating that a new amorphous molecular structure had developed. The larger 〈 R 〉 for the miscible blend indicates that the molecular chains are spread further apart, resulting in an increase in free volume to accommodate the new packing order. The single T g of this blend was lower than predicated by the Gordon‐Taylor equation.