Determination of the molecular weight distribution of polymers from equilibria in the ultracentrifuge

✍ Scribed by Th.G. Scholte

• Publisher: Elsevier Science
• Year: 1970
• Tongue: English
• Weight: 283 KB
• Volume: 6
• Category: Article
• ISSN: 0014-3057
• DOI: 10.1016/0014-3057(70)90183-7

✦ Synopsis

For determination of mol. wt. distribution from sedimentation--diffusion equilibria, the concentrations or the concentration gradients are measured in a number of places in the solution column for equilibria at various rotor speeds. The mol. wt. distribution is represented by a given series of tool. wts. Using a method of linear programming, a digital computer is made to find the weight fractions of the mol. wts. in the sample which fit best with the experimental data. A method of quadratic programming (least squares method) can be used just as well.

From a three-peak polystyrene sample (a mixture of three polystyrene samples with narrow distribution), the mol. wt. distribution has been determined in this way. The mol. wt. distribution of the same sample has also been determined by sedimentation velocity analysis atthe temperature where the sedimentation coefficient is independent of the concentration. The distributions obtained by these two methods agree well with each other and with the distribution obtained by gel permeation chromatography. The average mol. wts. M,, M,,, Mz and M.+ t calculated from these distributions also agree well with the values calculated from the average tool. wts. of the three original samples.