Miscibility and free volume behaviour of a number of polymer blends containing only thermotropic liquid crystalline polymers

An extensive study has been undertaken on a number of blends containing only thermotropic liquid crystalline polymers (TLCPs) as only components. The effect of the structure of the TLCPs on their miscibility and free volume properties (probed by positron annihilation lifetime spectroscopy) is presented in this work. Although all TLCPs studied are nematic and the experience with low molecular weight liquid crystals is that a common mesophase ensures miscibility, blends of TLCPs with each other show a wide range of miscibilities. The polymeric aspects of TLCPs such as their molecular chemistry, structure and conformation are also found to be important in determining miscibility in blends of such materials. Regardless of their various miscibilities, TLCP blends tend to display smaller, fewer free volume sites than expected from a weighted average. This is ascribed to the intrinsic affinity of nematic TLCPs. This differs from thermoplastic blends where it has been found that degree of blend miscibility alters free volume behaviour as a function of blend composition. (C) 2000 Elsevier Science Ltd. AU rights reserved.