Contribuicao para o Estudo dos Polimeros Liquidos Cristalinos Derivados da Celulose

The aim of this work to perform a study of liquid crystaline polymers, cholesteric, lyotropics and thermotropics that were obtained from some cellulose derivatives. The first polymers studied were some cellulose acetates with a weak molecular weight, measures of intrinsic viscosity were performed using Ubbelohde viscometers and through the use of Yamakawa Model the persistence lengh and the hydrodinamic diameter were obtained. The use of Flory and worm like chein models enable us to predict the behavior of the concentrated solutions. Experimental results were obtained on the concentrated solutions by using a polarizing microscope equipped with a thermostated platine. The influence of the solvent on optical properties of the mesophase was also performed upon hydroxypropylmethylcellulose and methylcellulose in trifluoroacetic acid with the aid of a polarizing microscope equipped with a platine and a photographic apparatus which allows photography of textures during heating and cooling cycles. The rflections properties were recorded with a monochromator (visible), mounted on the microscope and associated to a photo-multiplicator and a chart recorder. The optical behavior of these mesophases was found to be quite different from that found in literature. To study the effects of side chain structure on the properties of the liquid crystalline phase we report the preparation and characterization by Differential Scanning Calorimetry, Infrared Spectroscopy, Nuclear Magnetic Spectroscopy and Chemical Methods of several esters of hydroxypropyl-cellulose. This cellulose ether was selected as a parent compound because it is readily soluble in both aqueous and monaqueous media, furnishing homogenemous reaction conditions. The influence of the degree of substitution in mesomorphic properties was performed on n-butyric ester of hydroxypropycellulose and trifluoroacetopropylcellulose. A comparative study between aceto-xypropylcellulose protonated and deuterated and the trifluoracetoxypropycellulose was also performed. For hexanoate, heptanoate of hydroxypropylcellulose and acetoxypropylcellulose some rheological studies were done for the first time. The results were analyzed by using the models proposed by Doi, G. Marruci and more recently by A. F. MartinsAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga