A novel non-hydrolytic sol-gel route to low OH- and CH-containing organic-inorganic composites

Abstract

A new synthesis route to organic inroganic composites with low OH- and CH-content has been developed. Thus methacrylate-modified chlorosilanes were either homocondensed or cocondensed with fluoroalkyl-modifed chlorosilanes by a non-hydrolytic reaction with 2-methyl-2-propanol under formation of an inorganic network and hydrogen chloride and tertiary butyl chloride as well. Remaining chlorosilane groups were reacted by a second alcohol treatment to obtain air-stable, highly condensed, and low OH_containing sols. The condensation was followed by 29Si-NMR-spectroscopy, showing T2-content of up to 60% and and T3-content of up to 35% for trichlorosilanes and D2-content of more than 90% for dichlorosilanes respectively. The OH_content, which was estimated by FT-IR-spectroscopy, was lower than 10% referring to materials prepared by the conventionel aqueous sol-gel process. For further decrease of the CH-content copolymerization with fluorinated methacrylates was investigated. After addition of a photoinitiator transparent bulk materials with a diameter of 1 cm and a length of 1.5 cm were obtained by photopolymerization in closed UV-transparent containers using a Beltron UV apparatus with a low pressure Hg-Xe lamp. NIR -absorbance measurements were carried out and optical losses of bulk materials were determined. Cocondensed and copolymerized materials show low optical losses of 0.12 dB/cm at 1300 nm and 0.33 dB/cm at 1550 nm.