MECHANICAL SPECTROSCOPY OF SIDE-CHAIN LIQUID-CRYSTALLINE POLYMERS IN THE GLASS-TRANSITION RANGE

We report the first low-frequency mechanical relaxation measurement of molecular motions at temperatures near glass transition in side-chain liquid crystalline polymers (SCLCP) with a short alkyl spacer length of 3 in the cholesteric state. The dynamics of molecular motions invol ved in the liquid-glass transition of side-chain liquid crystalline po lymers in the cholesteric state has been studied. The effect of therma l history or physical aging has been investigated. The measured relaxa tion time when plotted against normalized reciprocal temperature in th e metastable equilibrium state shows that the molecular motion exhibit s a ''fragile'' or in other words a''highly cooperative'' character. T he interpretation of experimental results through two compatible theor etical models suggests that the molecular motions involved in the glas s transition are highly correlated in these SCLCPs. Comparison with th e data of a similar SCLCP that has a long alkyl spacer length highligh ts the change in segmental dynamics with alkyl spacer length. In addit ion, the sensitivity of mechanical spectroscopy makes it possible to m easure the variation of the glass transition temperature as a function of the chiral group amount.