A DENSITY FUNCTIONAL STUDY OF THE STRUCTURE OF SILANE COUPLING AGENT 3–AMINOPROPYLTRIETHOXYSILANE

Using density functional theory, we predicted the solution structure of the hydrolyzed 3-aminopropyltriethoxysilane (h-APS), which is a silane coupling agent commonly used in many industrial applications. We have located five stable minima on the potential energy surface of h-APS in which four of them axe "neutral", and the remaining one is zwitterionic (dipolax) in nature. Our calculations suggested that the stability of the most stable form of h-APS in water (denoted as II_N) arose from strong intramolecular OH center dot center dot center dot N hydrogen bond. The least stable form is the zwitterionic form (I_ZW), which is estimated to be over 90 kJ mol(-1) less stable than II_N. The factors governing the relative stabilities of different forms axe discussed.