Polystyrene chromatograms, molecular weight

Fig. 2 Typical polystyrene narrow molecular-weight range standard chromatograms and calibration curve.

Figure 9.7 shows separations under identical conditions using PSS SDV columns with 3 (Fig. 9.7a)-, 5 (Fig. 9.7b)- and 10 (Fig. 9.7c)-/i,m particle size columns. A polystyrene oligomer standard was injected and all analyses were performed in THF as the eluent. The much higher efficiencies of small particle size columns are obvious, which is important in the SEC separation of low molecular weight compounds such as additives, by-products, and resins. The reader should note that all chromatograms are area normalized and have the same Y axis to show the differences in peak width and height. 

First, we estimated the parameters a to be 0.01 and 8 to be 0.05. For the estimation of the standard deviation of the DP values, twenty chromatograms of NBS 706 polystyrene were measured and elution volumes at the distinguished per cent points of the integral curve of each chromatogram were calculated. Then, the value a was obtained to be 0.042 mL. The value 6 was estimated to be 0.1 mL, which corresponds to 0.3 % of the elution volume at the center of the calibration curve of this SEC system and 5 % difference of molecular weight. 

Figure 10 shows DRI and viscometer traces for the NBS 706 polystyrene standard. Based on the information from these two chromatograms in conjunction with the universal calibration curve, one can calculate the intrinsic viscosity EnJCv) and molecular weight M(v) at each retention volume as shown in... 

The chromatogram of Kraton 1107 shows the other components of the sample besides the major coupled diene S-l-l-S small amounts of "kill" polystyrene, uncoupled S-1 block copolymer, and material with higher molecular weight than that of SlIS are indicated. As indicated in Figures 2a and 3a, the LB polymers all showed a small polystyrene "kill" component and a high molecular weight shoulder on the block copolymer peak with a molecular weight of about twice that of the block copolymer. 

Calibration of Gel Permeation Chromatograph Polystyrene Calibration. A plot of molecular size in (S) versus elution volume for polysty-rene standards in dichloromethane showed deviation from linearity at about 2,200 which may be attributed to Imperfect column resolution, peak broadening, axial dispersion and skewing. The extensive tailing of the chromatograms of high molecular weight polystyrene standards observed in dichloromethane has also been reported in the literature (23-26). 

Gel permeation chromatograms were generated from a Waters Associates, Inc. GPC equipped with a refractive index detector. The following operating conditions were employed mobile phase, THF flow rate 1 ml/min., columns ICP, 10, 500, 100 A . Sample concentrations were prepared at 0.2% (w/w) a 100 microliter aliquot was used for molecular weight analysis. Standard polystyrene samples (Polymer Laboratories, Inc.) were used to create a calibration curve. 

Dead Volume. The dead volume difference between the viscometer and DRI must be accounted for. Otherwise systematic errors in Mark-Houwink parameters K and u can occur. In the previous paper (16), a method developed by Lesec and co-workers (38) based on injecting a known amount of a very high molecular weight polystyrene standard onto low porosity columns was used. From the viscometer and DRI chromatograms, the apparent intrinsic viscosity [h] was plotted against retention volume V. A series of [n] vs. V plots are then constructed assuming a range of dead volume, AV. 

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