Polystyrene molecular weight calibration curve

Herein are reported improved methods of molecular weight calibration where simultaneously, peak broadening parameters (a) are obtained through the use of multiple polydisperse molecular weight standards. There are two basic methods covered. The first and most reliable method employs the universal molecular weight calibration curve obtained using narrow MWD polystyrene standards. 

Figure L Molecular weight calibration curve for polystyrene an universal molecular weight calibration curve based on polystyrene ((%) [rj]Mw (U) w)...

The linear calibration method provides an equivalent molecular weight calibration curve to a peak position method of calibration using a series of polystyrene standards. 

Route 1 (a) Using the Mark-Houwink parameters of the PMMA test polymer in tetrahydrofuran, cthfia and thf A> construct the PMMA molecular weight calibration curve in tetrahydrofuran from the polystyrene HDV calibration curve by the use of Equation 2 where x is PMMA... 

Figure 2.14 Molecular weight calibration curves for porous silica microsphere columns. Chromatography conditions column, 10 X 0.78 cm mobile phase, tetrahydrofuran, 22°C flow rate, 2.5 ml/min detection, UV absorbance at 254 nm sample, 25 pi solutions of polystyrene standards, (a) Four individual columns showing four different calibration ranges (b) four columns in series with two distinct pore sizes (60,60,750,750A), providing a single calibration curve with a broader molecular weight range than the individual columns. (Adapted from Ref. 54 with permission.)...

The Q-factor approach is based upon the weight-to-size ratios (Q-factors) of the calibration standard and the polymer to be analyzed. The Q-factors are employed to transform the calibration curve for the chemical type of the standards (e.g. polystyrene) into a calibration curve for the chemical type of polymer under study. The inherent assumption In such a calibration approach is that the weight-to-size ratio is not a function of molecular weight but a constant. The assumption is valid for some polymer types (e.g. polyvinylchloride) but not for many polymer types. Hence the Q-factor method is generally referred to as an approximation technique. 

A universal calibration curve was established by plotting the product of the limiting viscosity numbers and molecular weight, Mw[iy], vs. the elution volume, EV, for a variety of characterized polymers. The major usefulness of the universal calibration curve was to validate individual molecular-weight values and to provide extended molecular-weight calibration at the ends of the calibration curve where fractions of narrow dispersion of the polymer being analyzed are not available. The calibration curve was monitored daily with polystyrene fractions certified by Pressure Chemicals. The relationship between the polyethylene fractions and polystyrene fractions was determined using the universal calibration curve. 

Working on the assumption that polystyrene standards are valid calibration standards for polyarylsulfones, the molecular weights (Mw) for resins IV and V were calculated from the molecular-weight distribution curves by the following equation. 

The Styragel 1000 column (1.0 x 42 cm) was prepared from resin swollen with benzene-methanol (90 10 v/v). Polystyrene standards were used for molecular weight calibration, and an exclusion limit of 28,000 was determined. The Sephadex-excluded asphaltene fraction was chromatographed on the Styragel 1000 column and a continuous elution curve was obtained from molecular weight 22,000 to 1000. 

Fig. 10.4 Molecular weight distribution curves, based on polystyrene calibration, of poly(l-chlorooct-l-yne)s obtained with catalysts (a) M0OCI4, (b) MoOCl4/Bu4Sn, and (c) MoOCl4/Bu4Sn/EtOH, in toluene at 30°C. Four successive batches of monomer (0.10 m) were added at 5 min intervals to the catalyst mixture ([M0OCI4] = 0.02 m), and completely polymerized at each stage. The curves, from top to bottom, correspond to successive stages...

Figure 4.1 Instrumental broadening of the chromatograms polystyrene standard reference materials. (A) Effect of solution concentration on observed chromatogram Mp = 1.43 x 10. Concentrations (a) 0.50 (b) 0.20 (c) 0.05 (d) 0.02 wt vol" %. 10 fim particles mixed gel (PS/DVB) column, 60 cm long (Polymer Lab. Ltd.) flow rate 1 cm min" 140°C ODCB mobile phase RI detector. (B) Separation of the individual oligomers by degree of polymerization, from 3 to 9. Mp = 580. Concentration 0.2 wt vol" %, flow rate 1 cm min" 140°C ODCB mobile phase RI detector. 2 x 10 /zm columns (PS/DVB gel) 50 and lOOA. (C) Polystyrene molecular weight/elution volume calibration curve. Experimental conditions as in (A).

Molecular weight was determined using polystyrene standards as calibration curve. 

The most widely used molecular weight characterization method has been GPC, which separates compounds based on hydrodynamic volume. State-of-the-art GPC instruments are equipped with a concentration detector (e.g., differential refractometer, UV, and/or IR) in combination with viscosity or light scattering. A viscosity detector provides in-line solution viscosity data at each elution volume, which in combination with a concentration measurement can be converted to specific viscosity. Since the polymer concentration at each elution volume is quite dilute, the specific viscosity is considered a reasonable approximation for the dilute solution s intrinsic viscosity. The plot of log[r]]M versus elution volume (where [) ] is the intrinsic viscosity) provides a universal calibration curve from which absolute molecular weights of a variety of polymers can be obtained. Unfortunately, many reported analyses for phenolic oligomers and resins are simply based on polystyrene standards and only provide relative molecular weights instead of absolute numbers. 

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