Phase behavior of side-chain liquid-crystalline elastomers and their precursors containing para-nitro azobenzene

Side-chain liquid-crystalline copolymethacrylates (PMm's), containing para-nitro azobenzene as the mesogenic group and 2-hydroxylethyl methacrylate (HEMA) as a comonomer, were synthesized by radical polymerization, and their corresponding liquid-crystalline elastomers (LCEm's) were prepared through chemical crosslinking. All of the polymers (PMm's) and the elastomers studied showed enantiotropic smectic A phases; the clearing temperature (T-i) of the PMm polymers decreased with increasing amount of HEMA, and the T-i of the corresponding LCEm's decreased compared to that of their precursors. Small-angle X-ray scattering studies on the copolymers quenched from their liquid-crystalline phases indicated that the characteristic distance increased with increasing amorphous component content and thus, the amorphous components were in between the smectic layers. (C) 2003 Wiley Periodicals, Inc.