The technique of thermally stimulated depolarisation currents (TSDC) was used to study the molecular dynamics in two samples of different molecular weight of a side-chain liquid crystalline polymer. The glass transition relaxation was carefully studied in these materials using the thermal sampling procedure. It is suggested that the amplitude of the deviation from the zero entropy prediction is related to the fragility of the glass, and a definition of fragility based on the TSDC results is proposed. Results previously obtained on other side-chain liquid crystalline polymers, on the low molecular weight organic glass former glycerol and on the orientationally disordered glass cyano-adamantane have also been discussed. Moreover, the physical ageing behaviour of the metastable glass below T-g was studied by the techniques of TSDC and differential scanning calorimetry. (C) 2000 Elsevier Science Ltd. All rights reserved.