SOME DYNAMIC FEATURES OF THE PREPARATION OF LIQUID-CRYSTALLINE ELASTOMERS

Liquid crystalline elastomers derived from siloxane polymers, PMHS and PEHS, were prepared following a two-stage reaction scheme to investig ate the effects of processing conditions and thermal treatment on meso morphic characteristics. The LC elastomer samples were analysed by FTI R, DSC, stress-strain relationship, polarized optical microscopy, and X-ray diffraction techniques. Key findings include: (1) Chain length o f the precursor siloxane polymer is critical to achieving a bulk align ment via stretching during the second-stage reaction; (2) the imposed strain is also critical to achieving a monodomain nematic character, w hich is completely recoverable upon heating beyond the clearing temper ature followed by cooling back to room temperature (i.e. thermal treat ment); (3) enthalpy is stored in an elastomer freshly prepared without an imposed strain, but the imposed strain helps to release the stored enthalpy, which can be almost completely released upon thermal treatm ent; and (4) while the stored enthalpy does not increase order paramet er (HOFA), its release through molecular relaxation contributes to an increased HOFA value.