Molecular Dynamics in Liquid Crystalline Side Chain Polymers

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Abstract
The static and dynamic dielectric properties of two liquid crystalline side chain polymers, one with a polychloroacrylate and one with a polyacrylate backbone and mesogenic side groups based on phenylbenzoate cores have been studied. The substitution of the polar chloro group at the main chain was done in order to get more information about the role of the main chain in the molecular dynamic processes. Dielectric permittivity measurements have been carried out with samples oriented in a magnetic field of 1.2 Tesla, in the frequency range 10 Hz to 10 MHz and a temperature range of – 50 °C to + 150 °C. A different behaviour is observed for the polyacrylate and the polychloroacrylate. The polyacrylate shows well resolved δ- and α-relaxations. For the polychloroacrylate the α-relaxation is extremely broad on the temperature and frequency scale. The δ-relaxation is also unusually broad and sets in very near to the clearing point. The dipole strengths of the relaxations are different for the two compounds due to the chloro group. The broadening of the relaxation processes for the polychloroacrylate is explained by a rapid increase of the viscosity below the clearing point.