Reaction kinetics and network characterization of UV-curing polyester acrylate inorganic/organic hybrids Ahmet Nebioglu 1 , Mark D. Soucek * Department of Polymer Engineering, The University of Akron, Akron, OH 44325, United States Received 21 March 2007; received in revised form 23 April 2007; accepted 16 May 2007 Available online 2 June 2007 Abstract Polyester acrylate inorganic/organic hybrids were prepared using a sol–gel precursor, coupling agent, and reactive dil- uent. The hybrids were cured via a UV-free radical initiator. Design of experiments (DOE) was utilized to investigate reac- tion kinetics and complex variable interactions. The effects of the silicate groups on the free radical photo-curing reaction kinetics were investigated utilizing a time-resolved Fourier transform infrared (FT–IR) spectroscopy and a differential scanning calorimeter equipped with a photocalorimetric accessory (photo-DSC). Microgel and inorganic network forma- tion during the UV-initiated free radical crosslinking reactions was suggested to describe the complex gel-point behavior. It was proposed that the formation of the inorganic silicate groups retarded the organic crosslinking reactions. The UV-cured inorganic/organic hybrid films exhibited more homogeneous film morphology compared to the organic counterparts. In the hybrid films, a core–shell like inorganic/organic particle morphology was observed. The UV-crosslinked organic phase forms the core, whereas, the inorganic silicate forms the surrounding shell. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Inorganic/organic hybrids; Polyester acrylate; Microgel; Morphology 1. Introduction In first UV-curing systems, unsaturated polyes- ters (UPEs) dissolved in styrene were used. The vol- atility of styrene and relatively slow curing rates has restricted the wide usage of these resins. However, due to the low cost UPEs find applications in wood coatings and in the glass-filled composite industry [1]. Current UV-cure coatings are mostly based on acrylated oligomers due to their relatively higher reactivity and lower volatility. Polyester acrylates are synthesized by reacting either the hydroxyl ter- minated polyesters with acrylic acid or the carboxyl terminated polyesters with hydroxyethyl acrylate [2]. Acrylate monomers are usually introduced as a reactive diluent to reduce viscosity and increase crosslink density. The UV-cured polyester acrylates are used as wood coatings, varnishes, lithographic and screen inks [3]. Mechanical properties of the unsaturated polyes- ters based coating films are greatly affected by the network structure of the crosslinked polymer. Vari- ous researchers have studied the reaction mechanism 0014-3057/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2007.05.035 * Corresponding author. E-mail address: msoucek@uakron.edu (M.D. Soucek). 1 Present address: Bomar Specialties, Winsted, CT 06098, United States. European Polymer Journal 43 (2007) 3325–3336 www.elsevier.com/locate/europolj EUROPEAN POLYMER JOURNAL