Physical ageing in glassy liquid crystalline poly(p-hydroxy-benzoic acid-co-ethylene terephtalate)

Glassy liquid crystalline poly(p-hydroxy-benzoic acid-co-ethylene terephthalate) is after rapid cooling from temperatures above Tg in a non-equilibrium state and exhibits physical ageing. It is shown that enthalpy and volume decrease with increasing annealing time. At the same undercooling, with respect to middle temperature of the major glass transition (Tgl), the rate of the equilibration process is significantly slower in the studied polymer than in an ordinary glassy amorphous polymer. The presence of a constraining ETP-rich phase exhibiting a 25 K higher glass temperature than Tgl may be the cause for this retarded enthalpy relaxation.