On the nature of “functional groups” in non-functionalized hypercrosslinked polystyrenes

Abstract

The paper discusses the assignment of the absorbance band at 1700cm−1 in FTIR spectra of hypercrosslinked polystyrenes. This band is exceptionally intensive in the spectra of networks obtained by post-crosslinking styrene-0.5% DVB copolymer, swollen in ethylene dichloride, with monochlorodimethyl ether up to the maximum possible crosslinking degrees of 300%, 400% and 500% in the presence of non-oxidizing catalyst SnCl4. Theoretically, in these networks each phenyl ring binds to neighboring phenyls through three, four or five methylene groups, respectively. Elemental analysis of the products seems to be deficient in C and H, thus allowing expectation of a surprisingly high percentage of oxygen. However, the traditional attribution of both the suspected high content of oxygen and the band at 1700cm−1 to aromatic carbonyl groups is incorrect. Treatment of hypercrosslinked polystyrenes with hydroxylamine, sodium bisulfite, ethyl orthoformiate or LiAlH4 do not result in disappearance of the absorbance at 1700cm−1 in FTIR spectra and emergence of corresponding characteristic new bands. Solid state 13C NMR spectroscopy also confirms the absence of CO moieties in the above hypercrosslinked polystyrenes. The absorbance at 1700cm−1 disappears, while new bands in the range of 1670–1650cm−1 emerge, in the spectrum of the sample with 500% crosslinking degree after the reduction of its benzene rings via Birch reaction. This allows suggesting that the band at 1700cm−1 and its shoulders are caused by hindered vibrations of carbon–carbon bonds and valence angles in the aromatic fragments composing the rigid network with extremely high extent of mutual connectivity.