A structural-thermodynamic study of trimethylsilylcellulose

Trimethylsilylcellulose (TMSC) samples were characterised in solution by osmometry, viscometry and gel permeation chromatography. The Mark-Houwink-Sakurada (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 the unit, thus indicating a high stiffness of the macromolecules in solution. Also, temperature's dependence on the limiting viscosity number and M-H-S coefficients, respectively, for TMSC in o-xylene, were studied. The exponent of the M-H-S equation is also higher than the unit and increases linearly with temperature. GPC studies indicated a relative high polydispersity of the studied samples, the polydispersity index ranging between 2 and 3. Change of the crystalline structure as the result of the silylation reaction was evidenced, the crystallinity of silyl derivatives depending on the substitution degree (DS). The viscous flow parameters for dilute solutions of trimethylsilylcellulose in o-xylene were determined in the 30-70° temperature range. Temperature dependence on the dynamic viscosity of the solutions obeys an Arrhenius-type equation in which the apparent activation energy is linearly depending on both solution's concentration and molecular weight. For the pre-exponential factor, no significant dependence on concentration and molecular weight was found, which was attributed to the very high stiffness of the macromolecular chains.