Synthesis of polyetherimide/silica hybrid membranes by the sol–gel process: inﬂuence of the reaction conditions on the membrane properties Analia I. Romero • Mo ´nica L. Parentis • Alberto C. Habert • Elio E. Gonzo Received: 8 November 2010 / Accepted: 7 February 2011 / Published online: 19 February 2011 Ó Springer Science+Business Media, LLC 2011 Abstract Hybrid polyetherimide (PEI)–silica membranes were synthesized. The aim was to obtain improved mate- rials for gas separation media. The inorganic material was prepared via the sol–gel method through the hydrolysis of tetraethoxysilane (TEOS). The inﬂuence of the reaction conditions on the ﬁnal membrane morphology and prop- erties were studied. Scanning electron microscopy (SEM), energy-dispersive X-ray analysis (SEM–EDX), and Fourier transform infrared spectroscopy (FTIR) were used to characterize the PEI and PEI–silica composite membranes. The evolution of TEOS hydrolysis and the condensation processes were veriﬁed by FTIR studies. The silica–poly- mer interaction was also analyzed. The SEM micrographs showed how the membranes distinct morphologies depen- ded upon synthesis parameters and preparation techniques (presence of coupling agent, TEOS polymerization in situ or not, silica content and membranes redissolution). The permeation rates of CO 2 , CH 4 ,O 2 ,N 2 , and H 2 through the pure polymer and hybrid membranes were measured and showed an increase of gas permeability for hybrid mem- branes but, the CO 2 /CH 4 and O 2 /N 2 selectivities decreased compared to PEI membranes. Introduction Hybrid organic–inorganic materials have been investigated as an interesting alternative to overcome the single compo- nent limitations, or to enhance mechanical, thermal and transport properties. In order to improve the performance of polymer membranes used in gas separation, inorganic materials were incorporated into the polymer matrix. Porous inorganic ﬁllers like zeolites and carbon molecular sieves (CMS) are used since they offer attractive permeation properties with permeabilities and selectivities, which are signiﬁcantly higher than polymeric membranes [1–6]. Ide- ally, the incorporation of small volume fractions of inorganic ﬁllers can result in a signiﬁcant overall membrane separation efﬁciency increase. Alternatively, hybrid membranes were proposed with the incorporation of non-porous nano-sized particles [4, 7–10]. The function of the ﬁller is to affect the molecular packing of the polymer chains, enhancing the separation properties of glassy polymeric membranes [11]. Hybrid organic–inorganic materials can be prepared using the sol–gel process. One method involves in situ reaction of an alkoxide with an organic polymer. Hydro- lysis and condensation reactions take place in the alkoxide resulting in inorganic networks bonded to the organic polymer [12, 13]. The composite material morphology and physical properties depends on the reaction conditions and the degree of compatibility between both components. When this hybrid material is designed for separation media, a key factor is to obtain a homogeneous structure. To achieve this objective, it is very important to have a membrane morphology control and to avoid phase separa- tion. A good interaction between the organic and inorganic materials may be reached with the use of compatibilizers or coupling agents, leading to the required homogeneity [12, 14–21]. A. I. Romero (&)  M. L. Parentis  E. E. Gonzo Facultad de Ingenierı ´a, Instituto de Investigaciones para la Industria Quı ´mica (INIQUI—CONICET), Universidad Nacional de Salta, Av. Bolivia 5150, A4402FDC Salta Capital, Argentina e-mail: romeroa@unsa.edu.ar; ailanarom@yahoo.com.ar A. C. Habert Programa de Engenharia Quı ´mica, COPPE/Universidade Federal de Rio de Janeiro, Cidade Universita ´ria, Cx. Postal 68502, Rio de Janeiro CEP 21941-972, Brazil 123 J Mater Sci (2011) 46:4701–4709 DOI 10.1007/s10853-011-5380-4