Dielectric relaxation of liquid crystalline dendrimers and liquid crystalline polymers with pendant nitro groups

• The dielectric relaxation was determined in a time-domain spectrometer between 100 and 295 K and from 0.1 to 1000 Hz for series of dendritic liquid crystalline polymers with scaffolds based on 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) of generations 0-3 with 4-((R)-1-methylheptyloxy)phenyl 4-{4'-[10-(hydroxy-carbonyl)decyloxy]-phenyl} benzoate as mesogen and for the second generation of dendrimers with 4-[10-(hydroxycarbonyl)decyloxy]-biphenyl 4-[4'-(2-(R)-octyloxy)-3-nitrophenyl] benzoate as mesogen. Dielectric data are also reported for a side-chain liquid crystalline polymer based on {4''-[(R)-(-)-2-octyloxyl-3-nitro-phenyl 4-(4'-(11-acryloyl-oxyundecyloxy)phenyl}benzoate. The low temperature subglass process (gamma) assigned to the spacer group was essentially insensitive to molecular architecture and to the presence of a pendant nitro group in the mesogen. The high temperature sub-glass process (beta) assigned to a 180 degrees flip of part of mesogen was only moderately sensitive to the molecular architecture. The introduction of a pendant nitro group in the mesogen led to a substantial increase in both activation energy and relaxation strength. The results suggest that the phenylene ring with the pendant nitro group participates in the beta process.

Nyckelord

dielectric relaxation

liquid crystalline polymers

dendrimers

2nd-order nonlinear optics

side-chain polymer

molecular-dynamics

poly(vinyl ether)s

main-chain

spectroscopy

behavior

phase

alignment

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