Thermal stability of hypercrosslinked polystyrene

As mentioned above, heating of hypercrosslinked polystyrene to 325°C for at least 1 h under protective argon atmosphere does not affect the porous structure and the apparent specific surfrce area of the material. StiU, this temperature should be considered as the material s upper stability limit. 

Interestingly, the presence of residual chlorine in the hypercrosslinked polymer enhances the yield of the final carbonizate (plot 1 in Fig. 7.48). It was found that the presence of carboxyl or sulfonic substituents in the aromatic rings of the polymer also enhances the yield of final carbons [207]. In fact it has been known [208] that sulfbnated styrene—DVB copolymers can be used for the preparation of carbonaceous adsorbing materials. However, because of the ehmination of heavy sulfonic substituents (over 40% of the material weight), the final yield of carbons is by no means hi er than in the 

This suggestion is directly corroborated by the emergence of very intensive signals of unpaired electrons in the electron paramagnetic (EPR) spectra of products pyrolyzed at 500-600°C [209]. Rupture of a stressed bond unavoidably results in a change of the conformation of the broken mesh, which places the formed radicals in positions unsuitable for their 

In general, pyrolysis of certain hypercrosslinked polystyrene materials at a temperature of about 600°C may result in interesting carbonaceous adsorbing materials with a yield of up to 55-60% within 50-60 min. The products maintain the spherical form of the initial materials and their overall texture, and acquire an exceptional mechanical strength of up to 8 kg per bead. They are basically nanoporous and show size-dependent adsorbing properties [207, 210]. In particular, they efficiently separate mineral ions in accordance with the new frontal ion size exclusion process 

The desweUing anomaly is particularly characteristic of the macroporous poly-DVB XAD-4, also containing a significant firaction of meso- and 

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