Porous Polymers

The preparation of capillary columns with porous polymers synthesized in situ was described by Hollis in 1973. These columns were quite active and only worked well for hydrocarbons; polar compounds elute with severe tailing. Using new coating techniques, it has become possible to coat porous polymers very efficiently on fused silica capillary columns.

Porous polymers are prepared by the copolymer-ization of styrene and divinylbenzene or other related monomers. The pore size and specific surface area can be varied by the amount of monomer added to the polymer. Several types of porous polymers have become commercially available under different names, including GS-Q, PoraPLOT Q and Supel-Q. It should be noted that the selectivity of some porous polymers in capillary columns does deviate strongly from the original polymer consisting of 100% styrene-divinylbenzene.

In general the polymer-coated capillaries are highly efficient and inert. Figure 7 shows the separation of a range of solvents with different functional groups; all the different types of compounds elute with good peak symmetry. A typical application for a porous polymer of the 'Q' type is shown in Figure 8, where

Figure 6 Impurities in 1,3-butadiene on an Al2O3/KCl PLOT column. Experimental details: column, 50 m x 0.25 mm fused silica, Al2O3/KCl, df = 4 ^m; oven, 50°C (1 min) p200°C, 10°Cmin~1; carrier gas, helium; injection, split; detection, FID. Peaks: 1, methane; 2, propane; 3, propylene; 4, isobutane; 5, butane; 6, cyclobutane; 7, unknown; 8, trans-2-butene; 9, 1-butene; 10, isobutene; 11, cis-2-butene; 12, 1,3-butadiene; 13, ethylacetylene; 14, hexane.

Figure 6 Impurities in 1,3-butadiene on an Al2O3/KCl PLOT column. Experimental details: column, 50 m x 0.25 mm fused silica, Al2O3/KCl, df = 4 ^m; oven, 50°C (1 min) p200°C, 10°Cmin~1; carrier gas, helium; injection, split; detection, FID. Peaks: 1, methane; 2, propane; 3, propylene; 4, isobutane; 5, butane; 6, cyclobutane; 7, unknown; 8, trans-2-butene; 9, 1-butene; 10, isobutene; 11, cis-2-butene; 12, 1,3-butadiene; 13, ethylacetylene; 14, hexane.

traces of acetaldehyde are measured in a hydrocarbon matrix.

Porous polymers are also available with different selectivities. By the incorporation of vinyl pyridine or methacrylate groups, the general selectivity can be changed and the polymer can be made much more polar.

Porous polymers have become very popular because of the high retention, the inertness and the selectivity that these materials provide. With porous polymers very volatile components can be separated at temperatures above ambient. In addition, one of the unique characteristics of porous polymers is their highly hydrophobic behaviour. The interaction with

Figure 7 Solvents on a porous polymer PLOT column. Experimental details: column, 10 mx 0.53 mm fused silica, PoraPLOT Q, df = 20 |im; oven, 100°Cp200°C, 10°Cmin~1; carrier gas, hydrogen; injection, split; detection, FID. Peaks: 1, methanol; 2, ethanol; 3, acetonitrile; 4, acetone; 5, isopropanol; 6, dichloromethane; 7, methylacetate; 8, pentane; 9, ethyl acetate; 10, hexane; 11, benzene.

Figure 7 Solvents on a porous polymer PLOT column. Experimental details: column, 10 mx 0.53 mm fused silica, PoraPLOT Q, df = 20 |im; oven, 100°Cp200°C, 10°Cmin~1; carrier gas, hydrogen; injection, split; detection, FID. Peaks: 1, methanol; 2, ethanol; 3, acetonitrile; 4, acetone; 5, isopropanol; 6, dichloromethane; 7, methylacetate; 8, pentane; 9, ethyl acetate; 10, hexane; 11, benzene.

water is very low, which results in a fast elution of water so that, for example, water elutes on a 100% styrene-divinylbenzene column before acetone and methanol.

The porous polymers are also recognized to be very inert, which makes them applicable for a wide range of compounds. A series of porous polymers of different selectivity has been commercialized and is nowadays available in 0.53, 0.32 and also 0.25 mm internal column diameter. Porous polymers have recently

Figure 8 Trace acetaldehyde in a hydrocarbon matrix. Experimental details: column, 25 m x 0.32 mm fused silica, PoraPLOT Q, df = 10 |im; oven, 140°C, carrier gas, helium, injection, split; detection, mass selective detection (MSD). Peaks: 1, air, argon and methane; 2, sulfur hexafluoride; 3, ethylene; 4, ethane; 5, water; 6, propylene; 7, propane; 8, acetaldehyde; 9, isobutane; 10, butane; 11, c/s-2-butene; 12, acetone; 13, isopentane; 14, pentane.

Figure 8 Trace acetaldehyde in a hydrocarbon matrix. Experimental details: column, 25 m x 0.32 mm fused silica, PoraPLOT Q, df = 10 |im; oven, 140°C, carrier gas, helium, injection, split; detection, mass selective detection (MSD). Peaks: 1, air, argon and methane; 2, sulfur hexafluoride; 3, ethylene; 4, ethane; 5, water; 6, propylene; 7, propane; 8, acetaldehyde; 9, isobutane; 10, butane; 11, c/s-2-butene; 12, acetone; 13, isopentane; 14, pentane.

Figure 9 Solvents on a porous polymer PLOT column. Experimental details: column, 25 m x 0.53 mm fused silica, PoraPLOT Q-HT, df = 20 |im; oven, 100°C p250°C, 5°C min"1; carrier gas, hydrogen; injection, split; detection, FID. Peaks: 1, methanol; 2, ethanol; 3, acetonitrile; 4, acetone; 5, isopropanol; 6, dichloro-methane; 7, pentane; 8, ethyl acetate; 9, hexane; 10, benzene; 11, cyclohexane; 12, toluene; 13, ethylbenzene; 14, propylben-zene; 15, decane; 16, butylbenzene; 17, undecane; 18, dodecane. Note the elution of volatile solvents.

Figure 9 Solvents on a porous polymer PLOT column. Experimental details: column, 25 m x 0.53 mm fused silica, PoraPLOT Q-HT, df = 20 |im; oven, 100°C p250°C, 5°C min"1; carrier gas, hydrogen; injection, split; detection, FID. Peaks: 1, methanol; 2, ethanol; 3, acetonitrile; 4, acetone; 5, isopropanol; 6, dichloro-methane; 7, pentane; 8, ethyl acetate; 9, hexane; 10, benzene; 11, cyclohexane; 12, toluene; 13, ethylbenzene; 14, propylben-zene; 15, decane; 16, butylbenzene; 17, undecane; 18, dodecane. Note the elution of volatile solvents.

become available in metal tubing, which has expanded their application even more as PLOT columns can now also be used in a process-type environment.

One of the latest developments is the improved stabilization of the 100% styrene-divinylbenzene porous polymers, which has resulted in the introduction of a high temperature material, called PoraPLOT Q-HT. This porous polymer can be used up to temperatures of 290°C, an increase of 40°C over the previously available material, and the bleed level of the polymer at lower temperatures has been reduced. The selectivity and inertness of the new polymer is not influenced by the stabilization process (Figure 9).

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