Physical aging in side-chain liquid crystal polymers: A DSC investigation of the enthalpy relaxation

The enthalpy relaxation of the glasses of two side-chain liquid crystal polymethacrylates was studied with physical aging experiments detected with differential scanning calorimetry. The experimental traces were fairly well reproduced in the framework of a recent configurational entropic model. The temperature dependence of the equilibrium structural relaxation times was obtained with a simultaneous fit of several different thermograms and compared with-the behavior found for the poly(methyl methacrylate) (PMMA). The comparison evidenced the stronger character of the two liquid crystal polymers, in the frame of the strong/fragile classification of glass-forming systems. At variance with the prediction of the energy landscape model, the heat capacity increment at the glass transition was greater than in PMMA, confirming some recent results on polymeric glass formers.