Photoresponsive Smectic Liquid Crystalline Multipods and Hyperbranched Azo Polymers

Liquid crystalline azobenzene containing
triped and tetraped monomers
were designed and synthesized and further used as B3 and
B4 type monomers to form hyperbranched polymers with tetraethylene
glycol as the A2 type comonomer. The mesophase characteristics
of the multiarm-star mesogens and hyperbranched polymers were analyzed
using various instrumentation techniques like differential scanning
calorimetry (DSC), polarized light microscopy (PLM) and variable temperature
XRD. The multipod monomers as well as hyperbranched polymers exhibited
thermotropic smectic liquid crystalline characteristics with a tendency
toward higher ordered smectic LC phases with increased branching.
The hyperbranched polymers exhibited lamellar organization even in
the as-solvent precipitated powder sample indicating higher extent
of nanosegregation. Their potential application as fast switching
photochromic materials was highlighted by carrying out isothermal
photoswitching experiments in the LC state. Reversible isothermal
smectic–isotropic phase transition could be achieved by UV
irradiation in <1 s in the multipod monomers, while it required
>2 s UV irradiation in the case of the hyperbranched polymers.