Spectroscopic characterization of sol–gel organo-siloxane materials synthesized from aliphatic and aromatic alcoxysilanes

In order to identify the absorption at 1310 and 1550 nm of CH and OH groups contained in photocurring organo-siloxanes materials, three materials have been prepared from aliphatic and aromatic alcoxysilanes employing both non-hydrolytic and hydrolytic sol–gel processes. The first material was synthesized via the hydrolytic sol–gel condensation of 3-trimethoxysilylpropylmethacrylate (MAPTMS) and a zirconia complex, and therefore contains OH groups. The second was produced from non-hydrolytic condensation of MAPTMS and SiCl4 using ZrCl4 as the catalyst, generating an OH free material. The third material was prepared from a hydrolytic co-condensation of MAPTMS and diphenyldiethoxysilane, and involved a three-step process: (1) separated pre-hydrolysis of the two alcoxides, (2) mixing of the two sols, and (3) further hydrolysis of the obtained mixture. This third material is therefore composed of both aromatic and aliphatic organic chains and contains residual silanol groups. Theoretical studies of the near-infrared spectra of the obtained materials clearly demonstrated that the exceptional performance of aromatic hybrid materials at 1550 nm does not originate from the low OH content as previously believed. It is in fact due to a shift of absorption resulting from the peculiar infrared absorption inherent to the aromatic groups.