THERMAL AND IR-DICHROIC PROPERTIES OF SIDE-CHAIN TYPE LIQUID-CRYSTALLINE ELASTOMERS

Several liquid-crystalline elastomers (LCEs) have been prepared by cro sslinking side-chain type liquid-crystalline polymers (precursors) in which mesogens are dangling from flexible main chains through spacers. Thermal properties and phase behaviour of the precursors and LCEs hav e been investigated by means of differential scanning calorimetry (d.s .c.) and polarizing microscopy. The glass transition and meso-to-isotr opic phase transition temperatures are slightly affected by an introdu ction of crosslinks to precursors. Orientation of the mesogens in the LCEs under uniaxial elongation has been evaluated in terms of order pa rameter for orientation (f) obtained by i.r.-dichroism measurements. A ll the LCEs under deformation show negative values off, meaning the or ientation direction of mesogens perpendicular to the axis of elongatio n. The value off changes greatly in the small deformation region, and reaches equilibrium at ca. 70% elongation, suggesting that a high degr ee of orientation for the mesogens in LCEs is achieved by a relatively small elongation. Dependence off on elongation ratio is not influence d by spacer length nor by crosslinking density, implying that the inte raction between mesogens is the most dominant factor for the orientati onal order of mesogens in the LCE system in this study. (C) 1997 Elsev ier Science Ltd.