Bluish-violet light-emitting liquid crystalline hyperbranched polymers using three trisalcohol B₃ monomers: Preparation, characterisation and structure–property relationship

Abstract

Bluish-violet light-emitting liquid crystalline (LC) A₂+B₃ type hyperbranched (HB) polymers composed of an internal 2,5-diphenyl-1,3,4-thiadiazole (DTD) as a mesogen were prepared by melt polycondensation of a dimethyl ester A₂ monomer with three trisalcohol B₃ monomers, and the effect of the B₃ monomer structures on LC and optical properties in the A₂+B₃ type HB polymers was evaluated. All the HB polymers 4a and 4b, having short aliphatic spacers between the central site of the B₃ monomers and the DTD unit, formed thermotropic smectic phases independent of feed mole ratios of A₂/B₃, and the phase transition temperatures and LC temperature ranges depended on the molecular weights of their HB polymers. However, in the HB polymers 4c, having long aliphatic spacers and a benzene ring between the central site of B₃ monomers and the DTD unit, only the HB polymer 4c1 prepared in the highest feed mole ratio of A₂/B₃ = 3/1 showed the LC property, probably due to steric hindrance of the B₃ monomer 3c. The HB polymers 4a and 4c displayed UV-vis absorption and photoluminescence spectra with bluish-violet light emission on the basis of the DTD unit, at almost the same wavelengths in chloroform solutions independent of the feed mole ratios of A₂/B₃ and the B₃ monomer structures, but the spectra of 4a and 4c in film displayed peak maxima at wavelengths depending on the feed mole ratios of A₂/B₃ and the B₃ monomer structures because of intermolecular interactions or aggregations.

Keywords:

• hyperbranched polymers
• trisalcohol B₃ monomers
• liquid crystalline property
• optical property
• structure–property relationship

Acknowledgements

The authors thank Ms. Michiko Egawa for her help in obtaining the elemental analysis data.