A dodecanediamine (DDA)-based new monomer, N,N-diallyl-N-propargyl-(12-N'-formylamino)-1-dodecylammonium chloride, on homo- and co-cyclopolymerization (with SO2) afforded cationic polyelectrolytes, which on acidic hydrolysis of the formyl group gave water-soluble polyelctrolytes. One of the allyl groups undergoes cyclopolymerization with either the propargyl or the other allyl group in competing pathways; the incorporation of the allyl group is found to be faster than the propargyl unit by a ratio of 4:1. Both the monomer and its precursor as well as the polymers were used to study the corrosion inhibition of mild steel by gravimetric and electrochemical methods in acidic and saline media at 60 A degrees C. The inhibitor molecules (at a concentration of 200 ppm) exhibited inhibition efficiencies (%IE) in the ranges 81-99 % in 1 M HCl, 97-98 % in 4 M HCl, 87-93 % in 7.7 M HCl, 68-91 % in 0.5 M H2SO4, and 84-92 % in 3.5 % NaCl. There is a considerable increase in the IEs by the monomers and polymers in comparison to the parent 1,12-DDA.