Thermally induced phase separation in liquid crystalline polymer/polycarbonate blends

Abstract

Thermally induced phase separation in liquid crystalline polymer (LCP)/polycarbonate (PC) blends was investigated in this study. The LCP used is a main-chain type copolyester comprised of p-hydroxybenoic acid and 6-hydroxy-2-naphthoic acid. Specimens for microscopic observation were prepared by melt blending. The specimens were heated to a preselected temperature, at which they were held for isothermal phase separation. The preselected temperatures used in this study were 265, 290, and 300 C. The LCP contents used were 10, 20, and 50 wt %. These parameters corresponded to different positions on the phase diagram of the blends. The development of the phase-separated morphology in the blends was monitored in real time and space. It was observed that an initial rapid phase separation was followed by the coarsening of the dispersed domains. The blends developed into various types of phase-separated morphology, depending on the concentration and temperature at which phase separation occurred. The following coarsening mechanisms of the phase-separated domains were observed in the late stages of the phase separation in these blends: (i) diffusion and coalescence of the LCPrich droplets; (ii) vanishing of the PC-rich domains following the evaporation-condensation mechanism; and (iii) breakage and shrinkage of the LCP-rich domains.