PHYSICAL AGING IN A THERMOTROPIC LIQUID-CRYSTALLINE POLYMER

The effects of physical ageing on the mechanical properties of a liquid-crystalline copolyester (LCP) were determined. Creep measurements in torsion as a function of ageing time were performed on macroscopically unoriented samples in the temperature range of - 60 to 180-degrees-C. Below the glass transition temperature (T(g) congruent-to 100-degrees-C), the results indicate physical ageing effects analogous to those of flexible polymers. However, the curvature exponent of the compliance as a function of creep time of the LCP is distinctly smaller. Above T(g), physical ageing remains present while additional annealing effects arise. The molecular interpretation of the time dependence of mechanical properties in LCPs cannot rely upon free-volume concepts as in flexible polymers, but might be based on new structural models that were recently introduced.