Determining the extent of reaction by29Si NMR of abrasion-resistant hybrid sol-gel coatings based on triethoxysilane functionalized organics

Diethylenetriamine, melamine, and low molecular weight branched polyethylenimine were functionalized separately with 3-isocyanatopropyltriethoxysilane. Coatings on polycarbonate were prepared from these compounds through the sol-gel process. The extent of reaction and the relative species concentration of the trifunctional silicon atom were obtained from²⁹Si CP-MAS NMR measurements. The sol-gel reaction was found to be limited by vitrification. A variety of silicon species was present in the vitrified coating. The extent of reaction could be increased by increasing the curing temperature, curing for longer times, and increasing the acid concentration. The extent of reaction was also found to be related to the basicity of the functionalized organic backbone.