Double Refraction of Flow Studies with Methyl Methacrylate Polymers in Solution

Abstract

An apparatus for the measurement of double refraction of flow is described. The magnitude of birefringence, expressed as the rotation of the plane of polarized light, may be measured to 0.05° under the best conditions with the assembly. The vortical angle and double refraction of flow of dioxane solutions of a series of fractionated polymers of α-methyl methacrylate have been measured at 25° over a concentration range of from one gram per liter to 50 grams per liter, depending upon the polymer under investigation. The specific birefringence, referred to the viscosity of the solvent, is a constant characteristic of each polymer in sufficiently dilute dioxane solutions. With the possible exception of behavior in such dilute solutions, the vortical angle is dependent upon concentration. Values of the rotary diffusion constant are calculated for each polymer from measurements of the vortical angle taken in dilute solutions. The lengths of the polymers are calculated from the rotary diffusion constants. They vary from 890A to 1880A. The shape and structure of the polymers are discussed from the point of view of their electrostatic and steric properties as evidenced by a molecular model. Tentative values of molecular weight and of length to width ratio are assigned. The viscosity of dilute dioxane solutions of the polymers has been measured at 25°. The specific viscosity increment at infinite dilution is estimated by extrapolation. This quantity is a linear function of the square of the length to width ratio, in partial confirmation of several theories of the viscosity of macromolecular solutions.