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 onl y thermotropic liquid crystalline polymers (TLCPs) as only components. The effect of the structure of the TLCPs on their miscibility and free volume p roperties (probed by positron annihilation lifetime spectroscopy) is presen ted in this work. Although all TLCPs studied are nematic and the experience with low molecular weight liquid crystals is that a common mesophase ensur es miscibility, blends of TLCPs with each other show a wide range of miscib ilities. The polymeric aspects of TLCPs such as their molecular chemistry, structure and conformation are also found to be important in determining mi scibility in blends of such materials. Regardless of their various miscibil ities, TLCP blends tend to display smaller, fewer free volume sites than ex pected 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 fu nction of blend composition. (C) 2000 Elsevier Science Ltd. AU rights reser ved.