Viscosity-Temperature Relationships for Dilute Solutions of Poly(cyclohexy1 Methacrylate) in Methyl Isobu tyl Ketone
Usually, the temperature dependence of the absolute viscosity q can be written as
where RTis the thermal energy and Q is the apparent activation energy of viscous flow which is constant over a limited temperature range. The meaning of the preexponential term A is related to a n activation entropy. This expression is of the Arrhenius form and has been called the Guzman-Andrade equation, which was theoretically derived by Eyring.' Thus, the absolute viscosity of a liquid is given by where N a n d h are, respectively, the Avogadro number and the Planck's constant, V is the molar volume of the liquid, and S is the entropy of activation of viscous flow. From eqs. (1) and (2) we obtain Measurements of absolute viscosities of dilute polymer solutions and their thermal variation are often employed as a way to characterize properties of macromolecules in solution.',2 Moore et a1.4-6 have related the A and Q parameters of the Guzman-Andrade equation to the polymer flexibility and thermodynamic properties of polymer-solvent systems. In this article, we have used eq. (1) to study the behavior of the poly(cyclohexy1 methacrylate) (PCHM) in methyl isobutyl ketone on the temperature range 283-313 K.
EXPERIMENTAL
Cyclohexyl methacrylate (Fluka purum) was washed three times with sodium hydroxide followed by distilled water; it was dried over anhydrous NazSO, and distilled ( < 25 mm Hg) in pure dried nitrogen.
A sample of poly(cyclohexy1 methacrylate) was obtained by radical polymerization using 1,2-azobisisobutyronitrile (Fluka puriss) as initiator in benzene, at 328 K. The polymer obtained was fractionated by solubility in the system pdioxanelmethanol. All fractions were purified by dissolving in benzene and reprecipitation with methanol. They were freeze-dried.
All solvents were analytical grade froE Fluka.
Number average molecular weights M, and weight average molecular weights z,, were determined by membrane osmometry and laser light scattering, respectively. In Table I, it can be seen the molecular weights and polydispersity index of the five fractions employed in this work.
Viscosities of both pure solvent and polymer solutions were measured, at several temperatures (283-313 K), by means of an modified Ubbelohde viscometer. The kinetic energy corrections were less than 0.2%. The bath temperature was regulated to k0.02 K. Intrinsic viscosities were obtained by graphical extrapolation of both q,,/c and In q,/c to zero concentration of polymer.