Search for perspective catalytic systems for synthesis of hypercrosslinked polystyrene sorbents
Abstract
This study was focused on resolving an important technical task, namely, designing of a convenient
method for preparing hypercrosslinked polystyrene sorbents. The developed method should be simple, onestep, reasonably priced and suitable for scaling up. It also should allow obtaining beaded polymers starting both from linear polystyrene and styrene-DVB copolymers. As a part of the formulated task, the bridging of dichloroethane-swollen styrene-0.7% DVB copolymer with monochlorodimethyl ether via Friedel-Crafts reaction has been re-examined. Experiments conducted with anhydrous catalysts (AlCl3, FeCl3, SnCl4, TiCl4 and ZnCl2) showed that basically it is possible to prepare hypercrosslinked sorbents with apparent inner surface area of 800 to 1000 m2/g provided one takes one mole of the catalyst per mole of the ether. However,
AlCl3 and FeCl3 cause degradation of the initial copolymer. The reaction proceeded too slow in the presence
of TiCl4 while ZnCl2 proved to be inactive. Sill, tin tetrachloride is the most convenient catalyst for scientific
researches. Unexpectedly, it was found out that FeCl3٠6H2O is capable of catalyzing the reaction of MCDE
with polystyrene, though the inner surface area of resulting polymers did not exceed 170 m2/g. This finding
suggested to examine aqueous acidic solutions of Lewes acids as catalysts. Of all the catalysts tested only
AlCl3 lost its activity in the presence of water because of complete hydrolysis till alumina, while FeCl3,
SnCl4 and ZnCl2 more or less maintain their catalytic capability. The best results were obtained when using a
solution of 70 g ZnCl2 and 3.5 g FeCl3 in 50 mL of concentrated hydrochloric acid. Being simultaneously a
catalytic system and a dispersion medium, this solution within 7-10 hours allows introducing 100% bridges
in styrene-0.7% DVB copolymer and obtaining a porous material with inner surface area as high as 1000
m2/g. The volume ratio of inorganic and organic phases may be varied from 3.5:1 to 0.4:1 every time obtaining polymers with the same surface area. Importantly, instead of beaded styrene-DVB copolymers one canuse a solution of linear polystyrene and, in addition, replace the ether with methylal, thus preparing beaded material with inner surface area of 800-1000 m2 /g. This procedure opens a way to the utilization of waste polystyrene packing material and its transformation into useful porous sorbents.
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References
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