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Abstract
Measurements of the twist viscosity coefficient of the main-chain nematic polymer poly (4,4′ dioxy 2,2′ dimethyl azoxybenzene nonanediyl) are reported. Temperature and mass dependences are studied in detail and analyzed in terms of existing theories. This viscosity scales as the square of the order parameter. The temperature dependence is found to be the same, for different molecular masses. The process is either purely activated or free volume controlled with a rather low “freezing” temperature of the director. For the mass dependence, a power law is observed. The mean value (∼ 4–5) of the exponent suggests a behaviour intermediate between those of rod-like and entangled flexible polymers. Two regimes with different exponents can however not be excluded.