Influence of the Functionality of Polyhedral Oligomeric Silsesquioxane–POSS Containing Glycidyl Groups on the Dispersion and Interaction With Epoxy Nanocomposites Marielen Longhi, 1 Vinicius Pistor, 2 Lucas Pandolphi Zini, 1 Eliena Jonko Birriel, 1 Sandra Raquel Kunst, 1 Ademir J. Zattera 1 1 University of Caxias do Sul – UCS/Post-Graduate Program in Processes and Technologies Engineering, Caxias do Sul – RS, Brazil 2 Federal University of Rio Grande do Sul – UFRGS/Institute of Chemistry –IQ/PGCIMAT, Av. Bento Gonc ¸alves, 9500, Porto Alegre – RS, 91501-970, Brazil For the polyhedral oligomeric silsesquioxane (POSS) nanocomposites with epoxy resins, the POSS function- ality is an important issue since these compounds will be diluted in the resin that will later undergo a chemical reticulation process. In this study, mono, tri and octa- functional POSS containing glycidyl groups were dis- persed in an epoxy resin by applying ultrasound. Based on the results obtained from the transmission electron microscopy, POSS tended to form an ordered phase to minimize the interfacial tension; however, this form was influenced by its functionality. The use of mono- functional POSS shows finer dispersion and promotes an increase in the resin glass transition temperature. However, the octa-functional POSS leads to improve- ment in thermal stability as seen in the degradation analysis. These results showed that the equilibrium of the dispersed nanoparticle is more evident for lower functionalized particles since higher functionalized ones hinder diffusion movements which ultimately form an ordered and dispersed phase in the resin during reticu- lation. POLYM. COMPOS., 00:000–000, 2016. V C 2016 Society of Plastics Engineers INTRODUCTION The use of polyhedral oligomeric silsesquioxane (POSS) for the preparation of thermosetting nanocomposites has been studied to obtain hybrid materials able to resist high temperatures [1], to promote an increase in mechanical properties [2] and to improve surface properties such as polymer hydrophobicity [3]. This kind of modification is convenient for high-performance thermosetting resins like epoxy resins, which are largely used in the manufacture of paints and adhesives. POSS oligomers are hybrid com- pounds with a typical size of 1.5 nm that have its core composed of inorganic silicon atoms surrounded by organic groups of the formula (RSiO1.5)n where n represents the number of functional groups present at the vertices of the blocks [4]. In the development of the nanocomposites it is possible to incorporate different POSS oligomers with dif- ferent organic groups at the periphery of these nanocages. Amines [5, 6], alcohols [7] and epoxy groups [8, 10] are the most widely employed functional groups for the develop- ment of nanocomposites with epoxy resins. This is due to the fact that the POSS is capable of incorporating different functional groups into the epoxy resin, leading to hybrid multifunctional structures [8]. The nanocage functionality is important since the thermosetting shape of the reticulated microstructure shows a tridimensional microstructure able to interact in any direction forming links or interacting at the interface of the inserted cages [11]. By adding POSS containing epoxy groups at its periphery, it could be observed that the nanocages have reduced their reactivity as compared with the resin due to the high spatial density over the nanocages periphery and the reduced mobility of the epoxy groups [8]. Besides, POSS has a tendency of under- going aggregation forming an independent phase. This fea- ture is mentioned elsewhere in literature, indicating the chemical affinity between the hybrid POSS compounds with the organic epoxy resin through the interface between the phases, which is dependent on the organic groups pres- ent at the POSS surface [3]. By comparing POSS containing the same functional group but with a different value of n, it is possible to observe different characteristics related to the agglomeration of POSS, which tends to minimize interfa- cial tensions with the resin. Monofunctional POSS tends to Correspondence to: A. J. Zattera; e-mail: ajzatter@ucs.br DOI 10.1002/pc.23991 Published online in Wiley Online Library (wileyonlinelibrary.com). V C 2016 Society of Plastics Engineers POLYMER COMPOSITES—2016