In-situ synthesis of organiceinorganic coatings via a photolatent base catalyzed Michael-addition reaction Arnaud Gigot a, b , Marco Sangermano b, * , Luigi Carlo Capozzi b , Kurt Dietliker c a Center for Space Human Robotics Polito, Istituto Italiano di Tecnologia, Corso Trento 21, 10129 Torino, Italy b Politecnico di Torino, DISAT, Corso Duca Degli Abruzzi 24,10129 Torino, Italy c ETH Zurich, Department of Chemistry and Applied Biosciences, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland article info Article history: Received 2 February 2015 Received in revised form 27 March 2015 Accepted 11 May 2015 Available online 19 May 2015 Keywords: Photolatent amine Hybrid nanocomposites Solegel process abstract Photolatent DBN derivatives were shown to be suitable catalysts for the in-situ preparation of novel organic-inorganic hybrid coatings. The formulations are based on organic resins crosslinked by a Michael reaction between acetoacetate modified oligomers and acrylic components, and an inorganic precursor undergoing a base-catalyzed solegel reaction. The size of the inorganic nanoparticles can be controlled by the addition of suitable coupling agents, thus allowing the design of hybrid coatings with optimized mechanical properties such as scratch resistance. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Based-catalyzed crosslinking processes are widely used for the curing of different resins [1]. Among them are the based-catalyzed addition of polyols to polyisocyanates providing polyurethanes [2], the ring-opening polymerization of epoxides by nucleophiles such as amines [3] or thiols [4], or the crosslinking of acetoacetate group containing polyesters with acrylates by a based-catalyzed Michael reaction [5,6]. The amidines DBU (1,5-diazabicyclo [4.3.0]undec-5-ene) and DBN (1,5-diazabicyclo[4.3.0]non-5-ene) are of the most powerful organic nitrogen bases [7]. In fact, these amidines combine a ba- sicity which is 3e4 orders of magnitude higher than that of con- ventional tertiary amines with high nucleophilicity resulting in a high catalytic reactivity, especially as catalysts for the Michael addition reaction [5,6]. The use of free amine catalysts results in formulations with a short pot life, which are difficult to handle under industrial appli- cation conditions. In order to obtain formulations with sufficient shelf life stability, the use of thermally latent or encapsulated de- rivatives of these amidines bases has been proposed [8,9]. The use of light for triggering curing process has proven outstanding advantages, due to the fact that this technology allows control of the curing both in time and space. However, in contrast to the photoinitiated radical or cationic polymerization, photolatent base (PLB) catalyzed processes have for a long time attracted little interest. It is only recently that photobase-catalyzed processes have found increasing attention and opened opportunities for a variety of new applications [10e17]. One reason for the slow acceptance of the photobase technology was the lack of suitable photolatent base catalysts, especially compounds liberating basic species that can act as real catalysts in base-catalyzed crosslinking reactions, such as DBN or DBU. Indeed, the majority of photolatent amines reported in the literature [11] are producing primary and secondary amines which are not suit- able for use as real catalysts due to the low basicity and a strong tendency to undergo addition reactions, e.g. to epoxides or acrylic double bonds. A few photolatent derivatives of tertiary amines have been evaluated at the very beginning of work on photolatent bases. In fact, the corresponding ketoprofen salts were proposed as photo- latent precursors of strong bases such as DBN or DBU [18,19], but were soon abandoned for use in industrial applications due to insufficient stability of formulations containing these salts. Inter- estingly, the same concept has recently been revisited and extended for the photochemical release of superbases by several research groups [20e25]. * Corresponding author. E-mail address: marco.sangermano@polito.it (M. Sangermano). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer http://dx.doi.org/10.1016/j.polymer.2015.05.019 0032-3861/© 2015 Elsevier Ltd. All rights reserved. Polymer 68 (2015) 195e201