Poly(phenylacetylene)
(PPA) bearing dendritic oligo(ethylene glycol) (OEG) as pendants was
synthesized, and its thermoresponsiveness and helical conformation
were investigated. Despite the steric hindrance of the bulky pendants
in the homopolymer PPA-OEG, the chirality could be efficiently transferred
from pendant alanine moieties to PPA main chain through ester linkage.
In order to examine the steric effect of pendants on chiral transformation,
a model PPA homopolymer PPA-Boc which carries less bulky moieties
was prepared for comparison. The chiroptical properties of these thermoresponsive
PPAs were further investigated by varying temperature to examine the
effects of their thermoresponsiveness. In addition, PPA copolymers
PPA-BDY bearing OEG dendron and fluorescent boradiazaindacene (BDY)
chromophore showed excellent thermoresponsive properties and interesting
fluorescence enhancement at elevated temperatures. To investigate
the rigidity effects of polymer backbone on the thermally induced
fluorescence enhancement, a nonchiral polymer carrying the same pendants
but with polymethacrylate as the backbone (PMA-OEG) was prepared.
It was found that the chiroptical and fluorescence properties of these
PPAs are dependent not only on their chemical structures but also
on the thermoresponsiveness