Molecular weight

of a polymer can be measured by several techniques and are separated into 2

categories: absolute and relative. Absolute methods, such as osmometry and

light scattering, are based on theoretical ovservations for molecular weight

calculations. Relative methods, which include intrinsic viscosity and size

exclusion chromatography, depend on calibration standards. Relative methods are

usually used as it is easy and have a low cost of operation.

Viscosity

measurements are used to determine the molecular weight of a polymer by

relating the polymer size to the viscosity. Due to frictional forces at the

walls of the capillary, a pure solvent experiences shear rate under laminar

flow. Depending on the size of a polymer particle in solution, it will

experience different shear rates as it flows through the capillary. This

increases the drag and viscosity, thus viscosity is related to the polymer

size. The relative viscosity, ?rel, of the polymer solution is given

by the ratio of the solution viscosity, ?, to the solvent viscosity, ?o.

Intrinsic viscosities can be calculated experimentally by using the Huggins (Equation

1) and Kraemer (Equation 2) relationships.

Equation 1: Huggins Equation 2: Kraemer

Using an Ubbelohde

capillary viscometer, the viscosity is measured by the time it takes for the

solution to pass through the viscometer. The specific viscosity is measured

using equation 3. After obtaining the intrinsic viscosity, the viscosity

average molecular weight, Mv, can be calualated using the

Mark-Houwink equation (equation 4).

Equation 3: Specific viscosity Equation 4: Mark-Houwink equation

In this experiment, the

intrinsic viscosity was obtained by plotting both the Huggins and Kraemer

equations and the viscosity molecular weight of the sample was then calculated.