Thermal Behavior and Dehydration Kinetic Study of SiO 2 /PEG Hybrid Gel Glasses Stefano Vecchio Ciprioti, 1 Michelina Catauro, 2 Flavia Bollino, 2 Riccardo Tuffi 3 1 Dipartimento S.B.A.I, Sapienza Universit  a di Roma, Via del Castro Laurenziano 7, Roma, I-00161, Italy 2 Dipartimento di Ingegneria Industriale e dell’Informazione, Seconda Universit  a di Napoli, Via Roma 21, Aversa, I-81031, Italy 3 Unit  a Tecnica Tecnologie Ambientali, ENEA – Casaccia Research Center, Via Anguillarese 301, S. Maria di Galeria (Roma), 00123, Italy Six different silica-polyethylene glycol (SiO 2 /PEG) organic- inorganic hybrid nanocomposites with different amounts of PEG 400 (6, 12, 24, 50, 60 and 70 wt.%) were synthe- sized by the sol-gel technique. Their thermal behavior was studied by thermogravimetry (TG) and differential thermal analysis (DTA) under a flowing argon atmosphere in a wide temperature range and their behavior was com- pared with those of the related materials with 60 and 70 wt.% of PEG, whose results were reported in a previously study. To identify all physical and chemical processes occurring in these promising materials, the gases evolved during TG experiments were analyzed at characteristic constant temperatures by FTIR. These measurements revealed that all the materials undergo a two-step dehy- dration (loosing water physically bound at temperature lower than 1008C) with overlapping of both TG and DTA curves, thus suggesting an identical behavior up to 2008C regardless the different content of PEG. A different behavior is observed at higher temperature, where three different exothermic effects were observed in the range 200–4508C accompanied by mass losses ranging from 6 to 37% for the SiO 2 /PEG hybrid materials. POLYM. ENG. SCI., 00:000–000, 2017. V C 2017 Society of Plastics Engineers INTRODUCTION Bioactivity can be defined as the ability of some materials with a definite chemical composition and structure to be incor- porated into living tissues when they are submitted to physiolog- ical environment, which consists in a series of chemical processes occurring in the material–living tissue interface. Some ceramic materials for medical application undergo a specific interaction with the physiological environment when implanted, which leads to the material integration in the living tissue. These latter materials are known as bioactive ceramics and include some calcium phosphates [1, 2], glasses, and glass- ceramics [3–5]. In this research area of biomedical field, silica- based ceramics receive great interest in the last 10 years since their substitution in the living tissues diseased or damaged aimed at inducing bone tissue regeneration. At this regards, hybrid bioceramics have significant properties derived by com- bining both inorganic and organic components, making them suitable for a wide range of medical applications [6–8]. Hydroxyapatite (HA), calcium phosphates, bioactive glasses belong to this class of materials together with related composite materials, which combine bioactive inorganic materials (able to form strong bonds to bone by reacting with physiological fluids) with biodegradable polymers (to form a silicon alkoxide matrix that may entrap active components favoring the drug delivery, like for cisplatin [9] and indomethacin [10, 11], or lanthanide complexes showing NIR-luminescence [12, 13]. Among these inorganic-organic biomaterials, silica-poly(ethylene glycol) (SiO 2 /PEG) has a good chemical stability due to the covalent bonds between the inorganic (silica) and organic (polymer) phase. On the other hand, over the past few decades PEG hydro- gels were extensively used as matrices for controlling drug delivery, as well as cell delivery vehicles for promoting tissue regeneration [14–17]. Recently, a shape-stabilized composite phase change material was prepared with the hazardous waste oil shale ash, in which PEG serves as the phase change material for thermal energy storage and SiO 2 acts as the carrier matrix to provide structural strength [18]. Bioactive glasses were usually prepared by both traditional melting and sol-gel methods [19, 20], being the advantages of using the latter stressed in a previous paper [21]. Many important properties of materials synthesized via the sol–gel technique are affected by many parameters (i.e., the chemical composition, the nature of the reagents, the solvents and catalysts used, the reaction temperature, and the rate of removal of solvents) [22]. In particular, the choice of catalyst influences the properties of the material. Hydrolysis of these materials is favored by acid catalysis since it may provoke the formation of linear Si–O–Si polymers and a more compact structure characterized by smaller pores in comparison with those obtained under basic catalysis conditions [23]. As a con- tinuation of the systematic extensive investigation carried out by our group (in particular by M. Catauro) on the synthesis, charac- terization and, in some cases, evaluation of bioactivity and bio- compatibility of inorganic silica-based gel glasses [24, 25] and silica-based organic-inorganic hybrid nanocomposited [26, 27], more recently, hybrid SiO 2 /PEG materials containing variable percentages in PEG 400 were synthesized and characterized by means of several techniques. FT-IR, NMR, XRD and SEM anal- yses showed that the SiO 2 /PEG hybrids are amorphous and homogeneous nanocomposites also when high PEG amount are embedded in the inorganic matrix. The organic and inorganic phases are linked by H-bounds between the –OH groups of the silica matrix and both the ether oxygen atoms and terminal –OH in the PEG chains [27]. Therefore, they belong to the first class organic-inorganic hybrid materials, according to Judenstein and Sanchez classification [28]. In vitro bioactivity and cytotoxicity Correspondence to: S.V. Ciprioti; e-mail: stefano.vecchio@uniroma1.it or M. Catauro; e-mail: michelina.catauro@unina2.it DOI 10.1002/pen.24561 Published online in Wiley Online Library (wileyonlinelibrary.com). V C 2017 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—2017