Correlation between molecular structure, free volume, and physical properties of a wide range of main chain thermotropic liquid crystalline polymers

Physical phenomena such as glass transition temperatures, melting points, a nd relaxational behavior have been determined for a wide range of thermotro pic liquid crystalline polymers (TLCPs) and polycarbonate (PC). Damping int ensities of rigid TLCPs during glass transition are greater than those of s emirigid and semiflexible TLCPs. Positron annihilation lifetime spectroscop y was also employed to evaluate free volume parameters of polymers, In gene ral, the positron annihilation lifetime spectroscopy (PALS) free volume par ameters show that all TLCPs have much smaller, fewer free volume sites comp ared with PC. Correlations were found between PALS free volume parameters a nd glass transition temperature, dynamic mechanical damping strength, and b ulk density where greater free volume parameters corresponded to higher gla ss transition temperatures, greater damping strength, and lower density. (C ) 2001 John Wiley & Sons, Inc.