Semi-Quantitative Evaluation of Steric Effect on Corrosion Inhibition Efficiency of Branched Alkyl Amines

Abstract

Steric effects of branched alkyl chains on the inhibition efficiency of amine inhibitors for the acid corrosion of iron were studied. Corrosion rates were determined on a pure iron electrode in 6.1M HCl solutions with and without the inhibitors at 30C by polarization measurements. The inhibitors adopted were monoalkyl amines (I), N-ethyl alkyl amines (II), and N dimethyl alkyl amines (III), of which alkyl groups are branched and unbranched chains. The inhibition efficiency of I and II decreased with an increase in the degree of branching of the alkyl group in the orders, n-butyl>isopropyl group, and n-butyl>isobutyl>sec-butyl>tert-butyl group. However, the efficiency for III decreased in the order, sec-butyl>tert-butyl>isobutyl>n-butyl group. The polarization data were semi-quantitatively analyzed in connection with the molecular coverage areas, the polar and steric substituent constants, and the basicity constants. The steric effect of the branched chain on the adsorption of the free amine increased with increasing the degree of the branching, resulting in lowering the inhibition efficiency for the anodic partial reaction. Further, this effect was enhanced in the order from I to II and markedly to III. The inhibition efficiency of III for the cathodic partial reaction increased with the degree of the branching in the alkyl group. This increase in the efficiency is attributed to the low hydration number for cations of III by the steric hindrance of the branched chain.

Effect of Isomeric Amine Chain Extenders and Crosslink Density on the Properties of Liquid Crystal Elastomers

“…In general, the key to determining the MW of LCOs synthesized by step-growth polymerization is the stoichiometric imbalance between the LC monomer and chain extender [36,40,41]. However, although the amine chain extenders examined in this study were primary amines, they showed different reactivities toward the diacrylate groups in the LC monomer during the aza-Michael addition reaction (i.e., n-butyl > isobutyl > sec-butyl), which is possibly because of the difference in steric hindrance [42]. Considering the different reactivities, the stoichiometry of LC monomer to chain extender was carefully adjusted to be 1.81:1 for LCE-N1, 1.33:1 for LCE-N2, 1.47:1 for LCE-I1, 1.03:1 for LCE-I2, and 1.01:1 for LCE-S1.…”

“…Hereafter, we refer to the LCEs prepared with n-BA as LCE-N1 or LCE-N2, with iso-BA as LCE-I1 or LCE-I2, and with sec-BA as LCE-S1, where 1 and 2 represent high and low crosslink density of the LCE, respectively. butyl), which is possibly because of the difference in steric hindrance [42]. Considering the different reactivities, the stoichiometry of LC monomer to chain extender was carefully adjusted to be 1.81:1 for LCE-N1, 1.33:1 for LCE-N2, 1.47:1 for LCE-I1, 1.03:1 for LCE-I2, and 1.01:1 for LCE-S1.…”