Substituent Effects on the Sol−Gel Chemistry of Organotrialkoxysilanes

• Published in: Chemistry of materials Vol. 12; no. 12; pp. 3624 - 3632
• Main Authors: Loy, Douglas A, Baugher, Brigitta M, Baugher, Colleen R, Schneider, Duane A, Rahimian, Kamyar
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.12.2000
• Subjects: Applied sciences; Exact sciences and technology; Inorganic and organomineral polymers; Physicochemistry of polymers; Preparation; Substituent effect; Silsesquioxane polymer; Molecular structure; Organic siloxane; Condensation polymerization; Experimental study; Property processing relationship; Hydrolysis; Structure processing relationship; Polyhedral molecule; Cyclic polymer; Sol gel process; Three dimensional polymer; Porosity; Chemical reactivity; Xerogel
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm000451i

Silsesquioxanes are a family of siloxane network polymers that have become important as vehicles for introducing organic functionalities into sol−gel materials. However, there has not been a systematic study of the capacity of organotrialkoxysilanes to form gels through the sol−gel process. In this study, we examined the sol−gel chemistry of organotrialkoxysilanes (RSi(OR‘)3) with different organic groups (R = H, Me, Et, Pr, i-Pr, n-Bu, i-Bu, t-Bu, hexyl, octyl, decyl, dodecyl, hexadecyl, octadecyl, cyclohexyl, vinyl, phenyl, benzyl, phenethyl, chloromethyl, chloromethylphenyl, and tridecafluoro-1,1,2,2-tetrahydrooctyl) with methoxide or ethoxide substituents on silicon, at varying monomer concentrations, and under acidic, neutral, and basic conditions. Gels were obtained from the sol−gel polymerization of the monomers with R‘ = Me and R = H, Me, vinyl, chloromethyl, chloromethylphenyl, hexadecyl, and octadecyl and R‘ = Et and R = H, Me, Et, chloromethyl, vinyl, dodecyl, hexadecyl, and octadecyl. Formation of gels, even with these monomers, was often circumvented by phase separation phenomena, giving rise to crystalline oligomers, resinous materials, and precipitates. Gels obtained from these polymerizations were processed as xerogels and characterized by solid-state NMR, microscopy, and nitrogen sorption porosimetry.