P– V– T properties of a polymer liquid crystal subjected to pre-drawing at several temperatures

Abstract

We have studied the copolymer of poly(ethylene terephthalate) (PET) with 0.6 mole fraction of p-hydroxybenzoic acid (PHB). It is a longitudinal polymer liquid crystal (PLC). A number of otherwise identical samples were subjected to drawing to achieve in turn 20%, 40%, 60%, 80% and 100% increase in length. The drawing was performed isothermally at 60, 100 and 140 °C. Pressure–volume–temperature ( P – V – T ) results have been obtained for pressures up to 200 J cm −3 and temperatures up to 150 °C or so. Parameters of the Hartmann equation of state have been evaluated. Drawing first results in an increase in specific (and also free) volume, then in a decrease caused by increased orientation of the PLC, and finally in an apparent increase caused by the appearance of voids. The tensile modulus E has been determined for all pre-drawn samples. It reflects the volumetric changes a rebours: the initial increase in specific volume results in lower E values, orientation in E increase, and void formation in a second decrease.