Cholesteric monomer and elastomers containing menthyl groups: Synthesis and phase behavior

The synthesis of a new cholesteric monomer (MLC) containing menthyl groups and a series of cholesteric elastomers (LCE1-LCE4) is described. Their chemical structures and purity were characterized by FTIR, 1H-NMR, and elemental analyses. The phase behavior and thermal stability were investigated by differential scanning calorimetry, polarizing optical microscopy, X-ray diffraction, and thermogravimetric analysis. By inserting a flexible spacer between the mesogenic core and the terminal menthyl groups, mesomorphism of MLC was realized. LCE1-LCE4 with low content of crosslinking unit exhibited cholesteric phase because of the introduction of the nematic crosslinking unit. This indicates that low levels of chemical crosslinking do not significantly affect the phase behavior and mesomorphism of the elastomers, and reversible mesophase transitions can be observed. In addition, with increasing the content of crosslinking unit, the corresponding Tg decreased for LCE1-LCE4, whereas their Ti did not remarkable change. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012