Fluoroalkyl end-capped oligomers possessing nonflammable and flammable characteristics in silica gel matrices after calcination at 800 °C under atmospheric conditions

Abstract

Fluoroalkyl end-capped N-(1,1-dimethyl-3-oxobutyl)acrylamide oligomer [RF-(DOBAA)n-RF] in silica nanocomposite can exhibit a nonflammability, even after calcination at 800 °C, through the formation of ammonium hexafluorosilicate during nanocomposite reactions. In contrast, the lack of formation of ammonium hexafluorosilicate during the usual composite reactions affords a flammable behavior for the RF-(DOBAA)n-RF oligomer in silica nanocomposite. Ammonium hexafluorosilicate is formed as a result of the dehydrofluorination of amido protons [-C(=O)NH-] in RF-(DOBAA)n-RF oligomer, with fluorine atoms in the oligomers catalyzed by both ammonia and silica nanoparticles in the composite reactions. In contrast, the lack of dehydrofluorination in the nanocomposite reaction under acidic conditions affords the usual flammable behavior for the oligomer. Fluoroalkyl end-capped N-(1,1-dimethyl-3-oxobutyl)acrylamide oligomer [RF-(DOBAA)n-RF] in silica nanocomposite can exhibit a nonflammability characteristic even after calcination at 800 °C, through the formation of ammonium hexafluor osilicate corresponding to −154.8 p.p.m. signal in 19 F MAS NMR spectra during the nanocomposite reactions; in contrast, no formation of ammonium hexafluorosilicate during the composite reaction affords a usually flammable behavior for RF-(DOBAA)n-RF oligomer in silica nanocomposite.