Abstract: The model geometries of reactive intermediates of the super-water-absorbent resin were determined by using ab inito UHF and density functional theory UB3LYP with 6-31G basis sets. The stability and reactivity of the two kinds of typical conformation isomers(1_a, 1_b and 2_a, 2_b) with their free radicals are obtained and analyzed. The calculation results show that the total energy of isomers 1a or 2_b is lower. The energy gap of isomer 1a is smaller comparing with the frontier molecular orbitals of four model systems. HOMO energy of 1a is higher, so it is easy to lose electrons. LUMO energy is lower and it is easy to receive electrons, which benefits the charge transfer. The spin density of free radical mostly concentrates on C2 or C3 and has no large diffusion. They are the key part of reactivity. The analysis to the complex with isomer 1a and acrylic acid molecule indicate that the polymerization reaction is easy to finish because of giving out heat.

Key words: Super-water-absorbent resin, Free radical, Ab initio, DFT