Molecular weight distribution curve generation

In order to convert a chromatogram into a molecular weight distribution curve, a calibration curve relating molecular weight to retention volume is required. Narrow MWD standards (polydlspersity, M /li, is usually less than 1.1) of the polymer of interest are used to generate retention volume curves. A one to one correspondence of peak retention volume with peak... 

Procedure Inject 50 p.L of the Sample Preparation, following the same conditions and procedure as described under Column Standardization. Using the Molecular Weight Distribution software of the data-reduction system, generate a molecular weight distribution curve of the sample. There is no measurable peak above a molecular weight of 22,000. Monomers... 

Other computer programs were used to plot the distribution profiles, interpolate these curves for extrapolation to zero concentration, generate the molecular weight distribution profiles, and to plot them. 

Figure 22 presents the GPC curves of polystyrenes obtained in concentrated emulsions at various temperatures. The molecular weight distribution broadens because of a greater amount of low molecular weight polymers generated in the bulk as the polymerization temperature increases. The greater the temperature, the greater is the coalescence and hence the amount of bulk phase formed. 

Figure 26 compares the conversion as a function of time in concentrated emulsion and bulk polymerization and shows that polymerization proceeds much faster in a concentrated emulsion. The concentrated emulsion has an internal phase ratio of 0.93 and a molar ratio of MAA/styrene of 0.036. The molecular weight distributions of the polymers generated by both processes are presented in Fig. 27, which shows that concentrated emulsion polymerization leads to molecular weights an order of magnitude higher. Since the copolymer composition changes with conversion, the GPC curves were recorded at the same conversion. 

Molecular weight distributions (SEC curves) of poiy-styrene samples with identicai peak moiecuiar weights generated via CDB-mediated styrene buik polymerization at 70 °C at 1 and 2000 bar, respect-iveiy, with aii other parameters being kept constant. ... 

The choice of a polystyrene standard is one of mere convenience in principle, any other polymer standard with narrow molecular weight distribution could be used to generate the imiversal calibration curve. Equation 23 can be made more useful by substituting the Mark-Houwink relationship. 

The last item above deserves to be expanded upon, since one of the most common questions asked is What does this viscosity curve say about the molecular-weight distribution of this material The answer is quite a bit, but much of the information is qualitative in nature rather than quantitative. It is often used to compare and/or rank samples rather than generate absolute numbers defining the distribution. 

Temperature leads to a similar effect and in Section 4.1 the temperature dependence of Qt will be discussed. Hence, within a given series of the same polymer, it is possible to generate the flow curves at all other molecular weights given the relation between h]q and M and the flow curve of a sample at a given M. (Note The breadth of the molecular weight distribution must be the same.)... 

At the high molecular weight end the theoretical curve lies below the experimental one. The present theory does not consider chain transfer and repolymerization ( 5) which must occur to some degree. For small amounts of chain transfer, the effect of repoly-merizatlon is to generate a high molecular weight tail on the initial distribution, which can be seen here. 

The next series of Figs. 5-7 illustrate the use of a relatively new aromatic modified terpene resin as a tackifier for natural rubber latex. Again, the properties of probe tack, quick stick, peel and shear adhesion were measured for various rubber/resin ratios. We observe that this resin tackifies the natural rubber latex quite well, yet the curves are substantially different from those generated with the beta-pinene resin emulsion. These differences can be attributed to differences in solubility parameter (caused by compositional differences) and molecular weight and distribution of the two resins. 

When an on-line viscometer is used together with the refractive index detector to generate the intrinsic viscosity [t]] in order to build the universal calibration curve. Sec. II.B, the intrinsic viscosity [t]] can also be used to determine the presence and degree of branching. This is done by plotting the log of [t]] versus log molecular-weight for each slice of the distribution. This plot is called the viscosity law plot, or the Mark-Houwink plot. It is described by the equation... 

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