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Thermotropic hydrocarbon main chain liquid crystalline polymers
Abstract
Two closely related series of hydrocarbon polymers that contain mesogenic units interconnected by flexible methylene spacers along the main chain were prepared. The liquid crystalline properties of these two series of polymers were studied by differential scanning calorimetry (DSC), polarized light optical microscopy (POM) and X-ray diffraction. The first series of hydrocarbon polymers having biphenyl mesogenic units and polymethylene spacers in the main chain were prepared by a nickel catalyzed carbon-carbon coupling reaction. Polymers with number average molecular weights in the range of 4000 to 6000 have been obtained. Homopolymers with spacer units varying from 6 to 10 methylene units and equimolar copolymers with 6/8, 6/10, and 8/10 methylene spacers were found to exhibit smectic mesophases. The effect of the variation of the lengths of the methylene spacers on liquid crystalline properties is discussed. In general, increasing the length of the methylene spacers is accompanied by a decrease in the isotropization temperature. An alternating odd-even effect in transition temperatures is also observed with the even members having higher isotropization temperatures than the odd members. Two different X-ray diffraction patterns for odd and for even membered homopolymers were observed for unoriented samples. The second series of hydrocarbon polymers having tolan mesogenic units and polymethylene spacers in the main chain were prepared by a palladium catalyzed carbon-carbon coupling reaction. Polymers with number average molecular weights in the range of 3000 to 4000 have been obtained. Four polymers with 6, 8, 10 and 12 methylene spacers were prepared and they were found to exhibit smectic mesophases. Lengthening the polymethylene spacer between the tolan mesogenic groups decreased both the melting points (T$\sb1$) and the isotropization temperatures (T$\sb{\rm i}$) and also narrowed the mesomorphic ranges.
Subject Area
Polymer chemistry
Recommended Citation
Sung, Ta-Cheng, "Thermotropic hydrocarbon main chain liquid crystalline polymers" (1991). Doctoral Dissertations Available from Proquest. AAI9132919.
https://scholarworks.umass.edu/dissertations/AAI9132919