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

Abstract

Physical phenomena such as glass transition temperatures, melting points, and relaxational behavior have been determined for a wide range of thermotropic liquid crystalline polymers (TLCPs) and polycarbonate (PC). Damping intensities of rigid TLCPs during glass transition are greater than those of semirigid and semiflexible TLCPs. Positron annihilation lifetime spectroscopy was also employed to evaluate free volume parameters of polymers. In general, the positron annihilation lifetime spectroscopy (PALS) free volume parameters show that all TLCPs have much smaller, fewer free volume sites compared with PC. Correlations were found between PALS free volume parameters and glass transition temperature, dynamic mechanical damping strength, and bulk density where greater free volume parameters corresponded to higher glass transition temperatures, greater damping strength, and lower density.

Rheology and relaxation processes in a melting thermotropic liquid–crystalline polymer

“…The DSC thermogram of LC‐5000 is shown in Figure 1, which illustrates a melting range from about 270 to 293°C and a nominal melting temperature of 275°C. The melting temperature T m determined here is slightly different from that (283°C) reported by Hiseh et al23 This is probably due to the different thermal history of the samples, and we did not investigate this discrepancy further. From Figure 1, we can see that the material is fully mesophasic above 293°C.…”

Application to Polymers

“…Hsieh et al [62] found that for a range of thermotropic liquid crystalline polymers, the greater the free volume measured by PAL the greater the chain mobility at Tg and the higher the value of tan 8 (damping strength) measured by dynamic mechanical analysis.…”

Free volume and damping in a miscible high performance polymer blend: Positron annihilation lifetime and dynamic mechanical thermal analysis studies

“…The high free volume in polycarbonate is due to methyl substituents that hinders chain packing and flexible carbonate linkages that reduces rigidity. Thus the impact strength of PC is high . Imperative contribution that relates free volume and damping property in PC has been reported by Bo Wang and coworkers .…”

“…Polymers with good impact strength will have good damping ability . It is necessary to highlight here the high impact strength of polycarbonate (PC) .…”