A comparative FTIR study of thermal and photo-polymerization processes in hybrid sol–gel films Plinio Innocenzi a, * , Giovanna Brusatin b a Dipartimento di Architettura e Pianificazione, Materials Science and Nanotechnology Laboratory, Universit a di Sassari, Palazzo del Pou Salid, Piazza Duomo 6, 07041 Alghero (Sassari), Italy b Dipartimento di Ingegneria Meccanica, Universit a di Padova, Settore Materiali, Via Marzolo 9, 35131 Padova, Italy Received 23 April 2003; received in revised form 25 August 2003 Abstract Controlling the organic polymerization in organic–inorganic hybrids is a key point in the development of new materials with high homogeneity of the nanostructure. The main difficulty is related with the achievement of a simultaneous control of the organic and inorganic network formation. Thermal and photocuring represent the main routes to form the organic chains when polymerizable organic groups are present in the hybrid materials. In the present work hybrid organic–inorganic films were synthesized from 3- methacryloxypropyltrimethoxysilane (MPTMS) cohydrolyzed with tetraethylorthosilicate (TEOS) and N-[(3-trimethoxysilyl)pro- pyl]ethylenediamine (TMESPE) or 3-(triethoxysilyl)-propylamine (TESPA). This an example of basic catalyzed hybrid material with a polymerizable methacrylate functionality whose micro-structure is modified by the amine groups. FTIR spectroscopy was used to compare the effects of thermal or photo-induced polymerization on the materials. TESPA and TMESPE showed a different catalytic effect on the condensation of the inorganic network, with TMESPE the more efficient one. The presence of a more extended silica backbone reduced the curing efficiency in TMESPE derived samples. UV curing was also very effective in catalyzing the inorganic condensation of un-reacted species still present in the film after the deposition. A photo-induced polymerization of the inorganic side was observed in the hybrid films. Thermal polymerization in TMESPE films induces the reaction between the secondary amine and C@O bonds in MPTMS, this reaction is, instead, not observed in films cured by UV radiation. Ó 2003 Elsevier B.V. All rights reserved. 1. Introduction UV irradiation has been widely used in sol–gel pro- cessing of coatings to achieve photoannealing of thin oxide films [1] and organic polymerization in hybrid organic–inorganic materials bearing a polymerizable organic functional group [2]. Exposure of hybrid films to UV radiation has been successfully applied in the fab- rication of micro-optical devices, such as diffraction gratings [3–5] and channel waveguides [6,7]. The photo-polymerization process can be generally extended to all the organic–inorganic hybrids containing polymerizable organic functionalities, for instance vinylic [8], epoxy [9] or acrylate groups [10,11]. Even if in principle the formation of an organic network cova- lently bonded to the inorganic side of the material could be quite easily achieved for all these different polymer- izable functionalities, great part of the research in UV curable hybrids has been concentrated on materi- als derived from 3-methacryloxypropyltrimethoxysilane (MPTMS). This alkoxide contains an acrylate group that can be thermally or UV cured with the help of a specific photoinitiator. Organic polymerization induces the formation of polyacrylate organic chains that are covalently bonded and interpenetrated with the silica backbone. MPTMS is commonly used because shows at the same time the properties of easy processing and a high optical transparency. The overall polymerization in a hybrid material is, however, a quite complex process because several syn- thesis parameters can affect the final structure. The ex- tent of the polymerization of the inorganic network is, for example, a quite crucial aspect because the organic polymerization is always a process in competition with the formation of the inorganic network [12]. The * Corresponding author. Present address: Dipartimento di Ingegne- ria Meccanica, Settore Materiali, Via Marzolo 9, 35131 Padova, Italy. Tel.: +39-079 972 0408; fax: +39-049 827 5505/+39-070 972 0420. E-mail address: plinio.innocenzi@unipd.it (P. Innocenzi). 0022-3093/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2003.09.043 Journal of Non-Crystalline Solids 333 (2004) 137–142 www.elsevier.com/locate/jnoncrysol