PHYSICAL AGING IN A THERMOTROPIC LIQUID-CRYSTALLINE POLYMER

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