The hydrophobic association and polyelectrolyte effect of hydrophobically associated water-soluble polymers (HAWSP) were eliminated in solvents containing 50%(volume percent concentration)1

3-propylene glycol

0.2 mol/L NaCl and water that could make molecules of HAWSP disperse in dilute solutions.Then the polymers of different molecular weights were split through the microporous membrane equipment with different aperture microporous membranes according to the principle of membrane aperture separation.The cumulative percentage of each fraction was calculated through the quantity of each fraction polymer solution which was measured by the curve of percolate quantity-filtration time fitted with a quadratic equation

and the concentration of each fraction polymer solution was measured by spectrophotometry.The Mark-Houwink equation[]=0.182M0.586 of HAWSP which was used to accurately determine the molecular weight of each HAWSP fraction

was calibrated through the static light scattering and capillary tube viscosity methods.The molecular weight distribution curve was determined according to the molecular weight (M) and cumulative percentage (W) of each fraction by using the 4-parameter equation curve.The method of microporous membrane grading to determine the molecular weight distribution of HAWSP was compared with the method of dynamic light scattering for measurement of particle size

the results of the two methods were consistent with each other.