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Polymer Science & Engineering
Year Degree Awarded
Liquid crystals, Polymers
Several hydroxy-terminated, low molecular weight polymers were reacted to form esters bearing mesogenic endgroups. The effect of the different repeating unit structures with a common mesogenic unit based on an oxybenzoylterephthalate dyad ester on the formation and properties of liquid crystals was studied by microscopic and thermal analysis techniques. The polymeric glycols used were polyethylene glycols (PEG), polytetramethyl ene glycols (PTMG), polybutadiene glycol (PB), and hydrogenated polybutadiene glycol (HPB) with molecular weight of 650 ^ 6000, in addition to 1 ,12-dodecanediol for the model compound. Conversion of the mesogenic dyad ester to a dyad containing a carboxylic acid group was shown to permit mesophase formation over a wide temperature range. The HPB product of this series was found to be a liquid crystalline elastomer with a low viscosity above the melting point, and with film forming ability. On examining the effect of endgroups on physical properties, it was found that both the length v of mesogen and hydrogen bonding interaction by carboxyl groups proved to be the most important factors to form liquid crystals with the PB and HPB polymers. Texture observation of macroglycol products on a polarizing microscope gave neither sharp T.. (clearing temperature) nor typical pattern of mesomorphic state. This result may be explained on the basis of the low stability of liquid crystal phase. These results were consistent with the differential scanning calorimetry (DSC) measurement that showed isotropic transition endotherms on heating but no peak on cooling. Low molecular weight precursors with liquid crystalline end groups associate to form high molecular weight polymers which resulted in films. Until now physical properties have been poor, but there is a possibility that further research in this area might provide a route to useful polymers which could be adaptable to the RIM process.