ORIGINAL PAPER Influence of synthesis conditions on the cross-link architecture of silsesquioxanes prepared by in situ water production route Valeria Tagliazucca • Emanuela Callone • Sandra Dire ` Received: 28 February 2011 / Accepted: 22 September 2011 / Published online: 4 October 2011 Ó Springer Science+Business Media, LLC 2011 Abstract The esterification reaction between carboxylic acids and alcohols has been used as the source of water for the hydrolysis-condensation reactions of difunctional and trifunctional organosilanes. Diphenylsilanediol (DPDO) has been reacted with methacryloxypropyltrimethoxysilane (MPTMS) and glycidoxypropyltrimethoxysilane (GPTMS) and the obtained products have been characterized by vibrational spectroscopy (FT-IR, FT-Raman) nuclear magnetic resonance (NMR) and gel permeation chroma- tography. The relation between water availability from the in situ water production process (ISWP) and silsesquiox- anes morphology has been evaluated in the case of DPDO/ MPTMS mixtures, changing molecular features of acids and alcohols. These measurements have shown that the pK of the carboxylic acid used in the esterification reaction has a valuable influence on the silanes cross-linking ability. Acids with low pK values and heteroatoms substituents favor the silane hydrolysis and allow the growth of high molecular weight species. Using acetic acid/ethanol mix- ture leads to the best results for DPDO/MPTMS reaction, with a narrow distribution of silsesquioxane species. Under the same conditions, the reaction of DPDO with GPTMS produces polymeric species and only avoiding the presence of the difunctional precursor allows to limiting the sils- esquioxanes species growth. Keywords Organoalkoxysilanes  Silsequioxanes  Crosslinking  Organic/inorganic hybrids  GPC  FTIR 1 Introduction The organoalkoxysilanes of the type R 0 n Si(OR) 4-n , with different R 0 organic functions and OR alkoxy groups, are widely employed as precursors for the preparation of silica- based hybrid organic/inorganic materials [1, 2]. Sils- esquioxanes obtained from hydrolysis-condensation of alkoxysilanes find several applications particularly in the field of coatings, which also represent the most popular commercial sol–gel products. The first applications of silsesquioxanes were related to the mechanical properties, like the production of scratch and abrasion resistant coat- ings for polymers [3]; however, in the last decades, many new applications have been proposed such as protective and functional coatings [4–8] matrices for dissolution of organic and biochemical compounds [9–13], materials for catalysis [14–17] micro-optics and electronics [18, 19]. The silsequioxane materials present several advantages, starting from the easy availability of organosilanes func- tionalized with both non-reactive organic groups, like the commonly used methylalkoxysilanes, and reactive func- tions leading, by organic polymerization, to interpenetrated networks [20]. The features of silane precursors allow the preparation of materials characterized by different cross- linking degree both for the siloxane network and the organic counterpart. Therefore, the possibility of playing with the extent of phase interaction leads to networks characterized by different structures, with the modification V. Tagliazucca  E. Callone  S. Dire `(&) Dipartimento di Ingegneria dei Materiali e Tecnologie Industriali, Universita ` di Trento, via Mesiano 77, 38123 Trento, Italy e-mail: sandra.dire@ing.unitn.it Present Address: V. Tagliazucca Department of Heterogeneous Catalysis, Max-Planck-Institut fu ¨r Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mu ¨lheim an der Ruhr, Germany 123 J Sol-Gel Sci Technol (2011) 60:236–245 DOI 10.1007/s10971-011-2599-0