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

摘要

The paper discusses the assignment of the absorbance band at 1700 cm~(-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 SnCI_4. 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 1700 cm~(-1) to aromatic carbonyl groups is incorrect. Treatment of hypercrosslinked polystyrenes with hydroxylamine, sodium bisulfite, ethyl orthoformiate or LiAIH_4 do not result in disappearance of the absorbance at 1700 cm~(-1) in FTIR spectra and emergence of corresponding characteristic new bands. Solid state 13C NMR spectroscopy also confirms the absence of C=O moieties in the above hypercrosslinked polystyrenes. The absorbance at 1700 cm~(-1) disappears, while new bands in the range of 1670-1650 cm~(-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 1700 cm~(-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.