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Cromatography Handbook of HPLC - Rizzi A.

Rizzi A. Cromatography Handbook of HPLC - John Wiley & Sons, 2005. - 14 p.
Download (direct link): chromatographyhandbook2005.pdf
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For PE, TCB at 135C [14]
log MPE = -0.329 + 0.99 log MPS
For PE, ODCB at 135C [29]
log MPE = - 0.332 + log Mps
For PP, TCB at 145C [30]
log Mpp = -0.0308 + 0.975 log MPS
Ethylene-vinyl acetate (EVA) copolymers were measured at 135C using TCB as the mobile phase and a refractometer and a differential viscometer as detectors [31]. A Mark-Houwink equation for EVA at 135C in TCB was
[77] = M J
and
= 0.053 (1 - 0.56 W) for 0 < W < 0.45
or
Polymer Analysis
843
= 0.053 (1 - 0.46W - 0.32W2) for full range
where W is weight fraction of vinyl acetate in EVA.
Poly(ether ether ketone) (PEEK) is insoluble in most organic solvents at room temperature. At high temperature, closer to its melting point, PEEK dissolves in benzophenone or
diphenyl sulfone.______SEC analysis was performed____________at___115C in a_______mixture of
phenol-trichlorobenzene (1:1) [32]. Poly(phenylene sulfide) (PPS) is also insoluble in most organic solvents below 200C, and it has been measured by SEC with 1 -chloronaphthalene as the mobile phase at 210C [33]._________________________________________________________________
D. Separation of Oligomers
1. SEC
Although in the SEC separation of synthetic polymers, the SEC chromatogram usually shows just a broad and continuous elution pattern, chromatograms of oligomers have several distinct peaks. Therefore, in the oligomer analysis, the separation into individual species (different degrees of polymerization) is an objective as well as the determination of MW averages.
In the separation of oligomers by SEC, the selection of pore sizes of packing materials in columns is very important. Among seven or eight different pore sizes that are now com-mercially available, three to four sizes can be used for the oligomer separation. Chromatograms shown in Fig. 2 represent the different elution profiles of epoxy resins with different pore sizes of packing materials. Epikote 1001 had higher MW averages than Epikote 828. A column of Shodex A801 has the exclusion limit of 2000 as PS and that of Shodex A 803 has 8 x 104 (see Fig. 1). Epikote 828 was separated well with columns of Shodex A801, but
(a) 2 1 (0 2 1
II / 0
5|
71
/J TL V p\
> ' I
(b) (d)
.-JV uU } Ju L.......
l l 1 l l i
Retention 1,1_Retention Volume, mL
Figure 2 Separation of epoxy resins with different porosity polystyrene gels. Sample: (a) and (c) Epikote 1001; (b) and (d) Epikote 828; column: (a) and (b) Shodex A-801 x 2; (c) and (d) Shodex A-803 x 2; mobile phase: THF. (Data courtesy of Shodex group, Showa Denko, Ltd.)
844
Mori
resolution was worse with columns of Shodex A803. On the other hand, most of Epikote 1001 eluted at the exclusion limit when columns of Shodex A801 were used because of smaller pore sizes of the columns. The resin was separated well with columns of Shodex A803. Figures on the chromatograms represent the degree of polymerization; that is, the number of monomeric repeating units.
In peak separation, it is possible to construct a calibration curve of peak retention volume versus MW for the oligomer of interest. The higher MW region can be extrapolated. Elution order of different oligomers of the same molecular size changed with mobile phase change because of the change of molecular sizes in different solvents and the adsorption effect. The examples are shown in Figs. 3 and 4 [34]. p-Cresol novolak resin oligomers in THF (see Fig. 3) eluted earlier than oligostyrenes in contrast with their elution in chloroform (see Fig. 4).
When the resolution between two adjacent peaks is poor, even though the selection of columns of appropriate pore sizes has been made, then one may couple together more columns of the same pore size [35] or use recycled SEC [36] to improve resolution. An example is shown in Fig. 5. Both chromatograms were obtained with the same packing materials having the same pore size, but the column lengths were different. Figure 5a was obtained with 16 columns of 1.5-mm id x 25 cm for which the number of theoretical plates was 103,000, and
Retention Volume , mL
Figure 3 Elution order of oligomers in THF mobile phase. Column: Shodex A-802 X 2; sample: (o) polystyrene, () n-hydrocarbon, (?) epoxy resin, () p-cresol novolak resin, (x) polyethylene glycol. (From Ref. 34.)
Polymer Analysis
845
Retention Volume, mL
Figure 4 Elution order of oligomers in chloroform mobile phase. Column: Shodex A-802 x 2; sample: (o) polystyrene, () n-hydrocarbon. (?) epoxy resin, () p-cresol novolak resin, (x) poly-ethylene glycol. (From Ref. 34.)
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