Synthesis of a soluble functionalized-silica by the hydrolysis and condensation of organotrialkoxysilanes bearing (β-hydroxy) tertiary amine groups with tetraethoxysilane

Abstract

The hydrolytic condensation of organotrialkoxysilanes containing (β-hydroxy) tertiary amine groups generates a significant fraction of intramolecular cycles and leads to the formation of closed structures. The aim of this study was to investigate if their co-condensation with a tetraalkoxy silane would take place by predominant intramolecular cyclization steps, eventually leading to functionalized silicas that can be dissolved in appropriate solvents. Co-condensation of tetraethoxysilane (TEOS) with the organotrialkoxysilane derived from the reaction of N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane with phenyl glycidyl ether, was performed in the presence of HCOOH using a thermal cycle attaining 150 °C. For TEOS molar fractions lower than 0.7, soluble functionalized-silicas containing up to about 25 wt% of inorganic silica chemically bonded to bulky organic groups, could be synthesized. The glass transition temperature of the organic part was close to 25 °C; it was inferred that the inorganic part was vitrified at the maximum temperature of the selected thermal cycle (150 °C). Most of the Si atoms supplied by the trialkoxysilane were present in fully condensed structures (T3), while those supplied by TEOS were present mostly as Q3 and Q 4 structures. These soluble functionalized-silicas may be used to introduce silica as a reinforcement of a polymer network. An example is shown, using an epoxy-diamine formulation. The equivalent of 10 wt% silica could be incorporated to the final network at the expense of a reduction of 26 °C in its glass transition temperature.