Reactive blending of polycarbonate and thermotropic liquid crystalline polymer

Abstract

Blending is to mix at least two polymers or copolymers, which is known to be an outstanding tool to obtain new materials with desirable properties because of its lower cost compared with synthesizing a new polymer. During melt blending of polymer having ester group like polycarbonate (PC), chemical reactions such as transesterification, depolymerization and repolymerization can occur because ester group is usually unstable at high temperature. These reactions would remarkably affect the properties of blends. Therefore, chemical reactions should be carefully controlled by choosing the proper preparation time, temperature and amount of catalyst. In this study, chemical reactions occurring between PC and LCP (PHB80/PET20) blends have been characterized and their influences on the properties of blends have been investigated. Firstly, miscibility has been investigated in PC/LCP physical blends in which chemical reactions is thought to be minimized. Physical blends were prepared in a twin screw extruder at 300℃. LCP contents were varied from 0-10 wt % each. The $T_g$ of PC phase in physical blends is not changed with the LCP contents, which indicates that physical blends are immiscible. Morphology of physical blends revealed by SEM indicates that the LCP phase of the spherical droplets is dispersed in PC matrix, and the interfaces between PC matrix and LCP droplet is clearly observed. Physical blends exhibit lower complex viscosity than that of PC so that LCP is thought to act as a processing agent. The logG```` vs. logG" plots also show that physical blends are immiscible. Enhancement of storage modulus relative to loss modulus at low frequency is apparent due to the contribution of interfaces. This kind of increase in storage modulus is more noticeable with adding LCP. In order to investigate effects of chemical reactions on the blend properties, reactive blends were prepared at 300℃ in a cylindrical flask by melt-mixing. In order to minimize any side reactions ...