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

• Published in: Polymer (Guilford) Vol. 42; no. 25; pp. 10027 - 10033
• Main Authors: Örtegren, J, Tidlund, J, Nykvist, M, Busson, P, Hult, A, Sen, S, Boyd, R.H, Gedde, U.W
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.12.2001; Elsevier
• Subjects: 2nd-order nonlinear optics; alignment; Applied sciences; behavior; Dendrimers; Dielectric relaxation; Electrical, magnetic and optical properties; Exact sciences and technology; Liquid crystalline polymers; main-chain; molecular-dynamics; Organic polymers; phase; Physicochemistry of polymers; poly(vinyl ether)s; Properties and characterization; side-chain polymer; spectroscopy; Liquid crystalline polymers; Dendrimers; Dielectric relaxation; End group; Optically active polymer; Branched polymer; Ester polymer; Thermotropic state; Experimental study; Side chain; Acrylate polymer; Biphenyl derivatives; Local mobility; Liquid crystal polymers; Linear polymer; Aliphatic polymer; Activation energy
• ISSN: 0032-3861; 1873-2291; 1873-2291
• DOI: 10.1016/S0032-3861(01)00558-4

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-octyloxy]-3″-nitro-phenyl 4-(4′-(11-acryloyloxyundecyloxy)phenyl}benzoate. The low temperature subglass process (γ) 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 (β) assigned to a 180° 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 β process.