Our study on antimicrobial ionenes revealed an unusual chemical property of quaternized linear polyethyleneimine (L-PEI) derivatives. The polymer backbone reactivity toward hydroxide strongly increases with the added number of repeating units. Methylated L-PEI and its oligomer containing four mers underwent rapid elimination in such mild alkaline conditions as 0.1 mol/L Na2CO3 solution at 25 degrees C, whereas two mer oligomer remained stable. The rigid oligomeric analog containing alkylated 1,4-diazabicyclo [2.2.2]octane subunits were even more reactive. The effect can be explained by the increased polarization of C-H bond that follows the chain elongation. Such hypothesis is well supported by a good correlation of reaction rates with H-1 NMR chemical shifts of eliminated hydrogens, what inspired discussion on possibly involved E1cB and E2 mechanisms. The observed correlation can be used to predict stability of polycations, which is an important issue in both biomedical and energy storage fields.