Arno Max Basedow

Fractionation of polymers by gel permeation chromatography: An experimental and theoretical approach

Summary The mechanism of gel permeation chromatography has been studied in a series of experiments performed on separation matrices of controlled pore glass with known pore structure and narrow pore size distribution, and using dextran fractions with accurately determined molecular weights and very narrow molecular weight distribution. Molecular weight calibration of the columns and effects of experimental variables on the shape of the elution peak and the peak broadening function were investigated, and the distribution and transport of polymer molecules between the mobile phase and the stationary phase within the pores of the separation material were discussed. An improved stochastic model for molecular weight calibration of separation matrices with cylindrical pores is developed as a function of the pore diameter.

General permeation chromatography equation and its application to taylor-made controlled pore glass columns

Abstract Permeation chromatography of narrow molecular weight dextrans ranging in weight from 1000 to 300, 000 daltons was performed on columns of controlled pore glass. In contrast to wide-pore substrates, the K vs . log M plots are monotonic, except for a short “upturn” of the curve for small values of K . The experimental results for all dextrans and poresizes obey a relatively simple general equation between K = 0.25 and 1.00. An expansion of the equation, allowing for width of pore size distribution extends the experimental fit of the equation to below K − 0.25 and demonstrates that the fundamental separation mechanism is not the result of a spectrum of pore sizes. The general equation is useful for pore size selection and for the design of composite systems used in the analysis of mixtures spanning wide molecular weight ranges.

Effects of mechanical stress on the reactivity of polymers: activation of acid hydrolysis of dextran by ultrasound

SummaryThe influence of ultrasonic irradiation on the kinetics and mechanism of acid hydrolysis of dextran is studied. The increase in the rate constants of the combined hydrolytic and ultrasonic degradation was investigated as a function of the molecular weight of dextran. For molecular weights higher than the limiting value for ultrasonic degradation the rate constants are proportional to the molecular weight raised to the power of 4/3; for molecular weights below the limiting value the rate constants are proportional to the molecular weight raised to the power of 5/6. The effects are discussed in connection with stretching forces which act on the polymer molecules as a result of ultrasonic cavitation.

Studies on the Enzymatic Hydrolysis of Dextran

SummaryThe enzymatic hydrolysis of well-defined dextran fractions is studied. The results show that the rate constants of degradation are proportional to the molecular weight for molecular weights higher than 5000; for lower molecular weights the rate constants decrease gradually. Enzymatic hydrolysis of dextran is not a statistical reaction, since the individual rate constants of bond cleavage increase from the midpoint of the chain towards both ends. The results are discussed in comparison with acid hydrolysis of dextran, and the characteristic differences between both reactions are pointed out.