Peak molecular weight

This simply relates to how linear the relationship between the peak molecular weight of narrow polystyrene standards versus elution volume fits a straight line. This is typically measured with the linear correlation coefficient, r. ... 

GPC chromatograms of AOT in benzene obtained with a 500 % + 100 A jjStyragel column set, and over a range of injected sample weights, are shown in Figure 1. The apparent peak molecular weight increases with the amount of sample applied to the columns. At higher sample loads, the value of Mn appears to ap-... 

On-line GPC technique for measurement of peak molecular weight of polystyrene... 

M is the peak molecular weight of a narrow distribution linear homopolymer and t is retention time. The equation is linear in the coefficients B, C, D and E. 

For a calibration curve of the form of Equation 1 the logarithm of the peak molecular weight of the standard is used and not simply the peak molecular weight. It is important to note that the error in the logarithm of the value is not the same as the error in the value itself. 

This can be shown ly plication of the error propagation equation (Equation 11). If the error in the peak molecular weight M is represented by the error variance, s and we let... 

We can detect a further complication from observations that some cationic polymerizations exhibit bimodal (two peaks) molecular weight distributions. This can happen if different active species (say, free ions and some form of ion pairs) engage in propagation or transfer reactions faster than they can come to equilibrium with each other. Under these circumstances there can be two effectively independent processes that govern the size of the macromolecules that are produced. If we ignore all these important complications we can write the following expressions for the rates of initiation (/ i), propagation (/ p), termination (R,), and transfer to monomer (Rv,m) ... 

Vapors of acrylonitrile were adsorbed into the dehydrated forms of different large- and medium-pore zeolites, to saturation levels of 46, 6, and 9 molecules of acrylonitrile per unit cell in dehydrated zeolite NaY, Na-mordenite, and silicalite, respectively. Subsequent reaction with radical initiator (aqueous solution of K2S2O8 and NaHSOs) produced intrazeolite polyacrylonitrile (no polymer was found in silicalite due to size constraints). The intrazeolite polyacrylonitrile could be recovered after dissolution of the host with dilute aqueous HF, and was very similar to bulk polyacrylonitrile. Gel permeation chromatography revealed a peak molecular weight of 19,000 for polyacrylonitrile recovered from the NaY host, and about 1,000 for the polymer from mordenite. 

The calibration of SEC requires the use of standard samples. A series of commercially available narrow MWD standards with known peak molecular weights (Mp) is normally used. The Mp value assigned to a cali-... 

Figure 1. Comparison of the peak molecular weights for a DRI and LALLS detector for the standard labeled Mp 17,000 by the supplier.

Significance of Peak Molecular Weight Corrections for Molecular Weight-Sensitive Detectors... 

Figure 2. Ratio of the viscometer peak molecular weight to the concentration detector peak molecular weight versus Mp value supplied with the standards. Open circles were determined assuming a Gaussian MWD for the standards, squares were determined from the DRI MWD, and triangles were determined from the UVMWD.

Light-scattering chromatograms of a narrow polystyrene standard with a peak molecular weight reported by the vendor of 1,030,000 are shown in Figure 1. Now, greater scattering intensity is clearly observed... 

The molecular weight of the standards is supplied by the producers, either with a single value which should correspond to that of peak maximum, or with a complete characterization data sheet containing the values of and determined by osmometry and light scattering. In the latter case, the peak molecular weight to be inserted in the calibration plot is the mean value A typical calibration curve for a three-... 

Additionally, molecular weight at the maximum of the differential form of distribution of mass fractions is often designated the peak molecular weight (Mp), and fraction percentages may indicate critical fractions of low- or high-molecular contributions. 

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