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ABSTRACT:The trimethylsilylcellulose (TMSC) samples were characterized in solution by osmometry, viscometry, and gel permeation chromatography. The Mark-HouwinkSakurada (M-H-S) equation coefficients were determined in chloroform, 1,1,1-trichloroethane, and o-xylene, in all cases the exponent "a" being higher than unit, this indicating a great stiffness of the macromolecules in solution. Also, the temperature dependence of the limiting viscosity number and M-H-S coefficients respectively for TMSC in o-xylene were studied. The exponent from M-H-S equation is also higher than unit, and increases linearly with the temperature. The GPC studies indicates a relative high polydispersity of the studied samples; the polydispersity index being situated between 2 and 3. The change of the crystalline structure as the result of silylation reaction was evidenced, the crystallinity of silyl derivatives depending on the substitution degree (DS), and the molecular weight. The viscous flow parameters for dilute solutions of trimethylsilylcellulose in o-xylene were determined in the temperature range 30 -70°C. The temperature dependence of the dynamic viscosity of the solutions obeys an Arrhenius-type equation in which the apparent activation energy is linearly dependent on both the solution's concentration and molecular weight. For preexponential factor no significant dependence on concentration and molecular weight was found. This behavior was attributed to the very great stiffness of the macromolecular chains.

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ABSTRACT:The purpose of this article is to report the characterization of a solution of triphenylsilylcellulose (TPSC) in terms of its rheologic properties by osmometry and viscometry to better understand processing parameters and conditions. This work is an extension of previous similar work on trimethylsilylcellulose (TMSC). TPSC was prepared in a medium of dimethylformamide (DMF) plus pyridine, under heterogeneous starting conditions and nitrogen atmosphere, by silylation of activated celluloses with triphenylchlorosilane at 115-120°C. The isolated and purified ethers were characterized according to their polydispersities and their substitution degrees, by osmometry and viscometry in various solvents. The Mark-Houwink-Sakurada equation coefficients were evaluated in 1,1,1-trichloroethane, chloroform, and o-xylene at 30°C and in o-xylene over the 30 -70°C temperature range. The values of 2.12-2.18 obtained for exponent "a" correlated with the very low values of pre-exponential factor (of 10 Ϫ12 order), indicating a high stiffness of the macromolecular chains. The viscous flow parameters for dilute solutions of TPSC in o-xylene were determined in the temperature range 30 -70°C. The temperature dependence of the dynamic viscosity of the solutions obeys an Arrhenius-type equation in which the apparent activation energy is linearly dependent on both the concentration and molecular weight of the solution. No significant dependence on concentration and molecular weight was found for the pre-exponential factor. This behavior was attributed to the great stiffness of the macromolecular chains.