Molecular weight retention volume, function

When the total polymer response, is known as a function of retention volume, the molecular weight distributlon can be obtained in the usual manner with the appropriate molecular weight calibration curve. The molecular weight calibration curve can be obtained (a) by using the Runyon (65) copolymer molecular weight scale approach, or (b) by using a hydrodynamic volume approach if the Mark-Houwink constants for the polymer of interest are known or can be determined, or (c) by using a hydrodynamic volume approach in conjunction with an on-line viscosity detector. 

Figure 16 shows the viscometer and DRI traces of another star-branched polystyrene. This sample contained about 12% of the starting linear arm precursor which eluted at retention volume ca. 52 ml. The kinetic molecular weight of the linear precursor was 260,000. The results obtained for the individual peak through the SEC/Viscosity methodology are summarized in Table 7. It is seen that the measured of the linear arm is very closed to the kinetic value. The average functionality of this star polymer is calculated to be f = 10. 

The chemical lumping pattern shown in Figure 4 is very similar to the plotting of distillation temperatures vs. composition, a technique commonly used in petroleum refining to simulate the composition of distillate as a function of temperature. Since SEC includes nonvolatiles, information on their size distribution is also shown. In each chemical lump the molecular weight decreases as SEC retention volume increases. The individual chemical lump has a SEC separation pattern similar to a distillation temperature vs. molecular weight plot, a technique used in petroleum refining to illustrate the composition of various distillation cuts. 

Fig. 7. Interrelation between molecular weight and retention volume for macromolecules of different functionality at chromatography in the exclusion (1-3), the critical (4), and the adsorption (5) separation modes 59). In the general case, the distribution coefficient Kd is a function of the pore size D, the chain length N, the interaction energy with the pore wall of the backbone segments 0 and the terminal segment 0f containing the functional group (zones 1,2 and 3 correspond to the cases shown in Fig. 2)...

Values of Re can be calculated from Equation 6 for narrow fractions of known molecular weights and plotted as a function of Vr, the retention volume. n and w can then be calculated from the GPC molecular-size distribution curve for unknown whole polymers. To obtain /W from Equation 8 requires a value for q. 

Liebman et al. (/ 7) detected the glass transition of poly(vinyl chloride) stationary phases by recording the separation of cisitrans isomers as a function of temperature. It was found that no separation could be achieved in the vicinity of Tg while separation was possible both above and below Tg. Similar discontinuities in the plots of relative retention volumes were reported by Yatmunoto et id. 18) for poly carbonate stationary phases of differing molecular weights. 

When one of the constituents, A or B of a copolymer A-B, has an ultraviolet (UV) absorption and the other does not, a UV detector-refractive index (RI) combined detector system can be used for the determination of chemical composition or heterogeneity of the copolymer. A point-to-point composition, with respect to retention volume, is calculated from two chromatograms and a variation of composition is plotted as a function of molecular weight. The response factors of... 

Fig.l Calibration curve of GPC-SEC column. Logarithm of the molecular weight, M, is plotted as a function of the retention time (volume) (Ti ). 

The primary purpose of GPC-SEC is to obtain a retention curve that represents the molecular weight (MW) distribution of the analyte. Because the retention volume is a linear function of the partition... 

Figure 11. Copolymer composition (Plv), average styrene sequence length (Ns) and number average molecular weight as function of the retention volume. Molar feed composition is 0.90. PS is the polystyrene calibration curve. Key , Mn A>...

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