Azoxybenzene mesogen

Blumstein and coworkers studied the cholesteric behavior of polyesters with azoxybenzene mesogenic units and the same chiral spacer, (+) 3-methyladipic acid. They could clearly observe oily streak textures, which are typical of low molecular weight cholesterics, for the following homopolymer and copolymers ... 

Recently Blumstein and coworkers reported on the thermotropic properties of a series of main chain copolyesters with different azoxybenzene mesogenic units and flexible spacers consisting of varying ratios of (-I-) 3-methyl adipic acid and 1,12-dodecanedioic acid. Melting temperature of the copolyesters showed minimum values for either the 50/50 compositions or the 25/75 combination of the two spacer components, depending on the nature of the mesogenic units. However, Tj tended to decrease linearly with the content of the 1,12-dodecanedioic acid unit, except in one case. They also observed that the cholesteric pitch of the copolyesters seemed to increase as the concentration of the achiral unit, dodecanedioic acid, increased. Similar observations were reported earlier by Strzelecki s group... 

A liquid crystal polyester having azoxybenzene mesogenic units and decamethylene spacers was subjected to a proton NMR study after the polymer was aligned in a magnetic field of 1 Tesla Below the melting point of the polymer, the NMR spectrum... 

A.Blumstein, S.Vilasagar, S.Ponrathnam, S.B.Clough, and R.B. Blumstein, Nematic and cholesteric thermotropic polyesters with azoxybenzene mesogenic units and flexible spacers in the main chain, J.Polym.Sci., Polym.Phys.Ed. 20 877 (1982). 

STRUCTURE-PROPERTY RELATIONS IN FLEXIBLE THERMOTROPIC MESOPHASE POLYMERS I. PHASE TRANSITIONS IN POLYESTERS BASED ON THE AZOXYBENZENE MESOGEN... 

R B Blumstein. Nematic and Cholesteric Thermotropic Polyesters with Azoxybenzene Mesogenic Units and Flexible Spacers in the Main Chain. J.Poly.Sci Poly.Phys. 20 877 (1982). 

Thermotropic Polymeric Liquid Crystals (PLCs) which are formed by regularly alternating mesogenic elements and flexible spacer groups in the main chain are currently the focus of intensive investigation The standard meso-gens, such as biphenyl, stilbene, azo or azoxybenzene derivatives, which form the core of low molecular mass liquid crystals (LMLCs), are used in synthesis of PLCs as well. 

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