Comparative corrosion inhibition performance of diallyl amine-based cyclopolymers bearing secondary, tertiary and quaternary nitrogen's motifs in 1 M HCl

In the present work, diallylammonium chloride (3), methyldiallylammonium chloride (4), and diallyldimethylammonium chloride (5) were cyclopolymerized to produce the corresponding polymers 6, 7, and 8, respectively. The synthesized polymers were examined as corrosion inhibitors for 304L stainless steel (304L SS) in 1 M HCl after being physically and spectroscopically characterized (FTIR, ¹H and ¹³C NMR). TGA evaluated the thermal stability of these polymers. According to chemical and electrochemical investigations, the investigated polymers have outstanding corrosion-inhibitory behavior, and their inhibition potential was as follows: 6 (94.42%) > 7 (88.83%) > 8 (79.22%) at 50 ppm (chemical data). Many ideas have been put up to explain the order mentioned above of corrosion inhibition potential, including the impact of the methyl group(s) on solubility, steric hindrance, deprotonation, and back donation tendency of quaternary nitrogen. The results indicate that tested polymers become effective by adhering to metallic surfaces, and this adhesion adheres to the Langmuir isotherm model. They act as an interface and mixed-type inhibitors by adsorbing the active sites and blocking them and raising the barrier for the charge transfer mechanism. According to thermodynamic studies, chemisorption is the principal process by which polymers 6–8 adsorb on metallic surfaces. DFT study manifests that a five-membered nitrogenous heterocycle ring substantially influences back donation.