Sulfonated syndiotactic polystyrene: sorption of ionic liquid in the amorphous phase and of organic guests in the crystalline phase Agata Dembna a , Vincenzo Venditto b *, Alexandra R. Albunia c , Rosa Califano b and Gaetano Guerra b Fourier Transform Infrared spectroscopy (FTIR) and Wide-Angle X-Ray Diffraction (WAXD) measurements have clearly established the occurrence of a dual sorption ability of sulfonated syndiotactic polystyrene samples, which exhibit the nanoporous d crystalline phase. In fact, large uptake (up to 20–30 wt%) of ionic liquid (IL; e.g. 1-ethyl- 3-methylimidazolium dicyanamide) occurs only in the hydrophilic amorphous sulfonated phases and does not disturb the hydrophobic nanoporous crystalline d phase. On the other hand, a large uptake of organic guests (e.g. naphthalene) occurs prevailingly in the nanoporous hydrophobic crystalline phase, independently of the presence of the IL in the amor- phous phase, eventually leading to the formation of syndiotactic polystyrene co-crystalline phases. The thermal stability of IL can be largely increased by their inclusion in the amorphous phase of sulfonated syndiotactic polystyrene films. Copyright © 2012 John Wiley & Sons, Ltd. Keywords: syndiotactic polystyrene; porous crystalline phases; host–guest systems; ionic liquid; thermal stability; polymer phase transitions INTRODUCTION New materials presenting novel properties have been developed in the last decades on the basis of microphase separation at the mesoscopic scale. Excellent examples are represented by copoly- mers, like styrene–butadiene–styrene, a common elastomer used for shoe soles, car tires, and adhesives, [1] or Nafion (DuPont), a material for fuel cell membranes characterized by nanoscale phase separation into conducting hydrophilic domains and structural hydrophobic domains, which combines conductivity with good mechanical properties. [2] Recently, further interest has been attracted by the combination of ionic liquid (IL) with polymers, [3–8] either by incorporating an IL into a polymer matrix [3–6] or into one phase of a diblock copolymer [7] or by synthesizing polymeric IL block copolymers. [8] Indeed, the properties of membranes that combine the mechanical properties of polymers with the high conductivity of IL, that is, salts with low melting temperatures, low vapor pressure, high thermal, chemical, and electrochemical stability, are highly enhanced. In this article, we have investigated the possibility to include IL into syndiotactic polystyrene (s-PS), a semicrystalline thermoplastic polymer exhibiting hydrophobic nanoporous crystalline phases. [9] Polymeric nanoporous crystalline phases are generally achieved by guest removal from host–guest co-crystalline phases. Their ther- moplastic nature allows an easy processing to suitable products like films, membranes, foams, and aerogels as well as allows their easy recycling, and their polymeric nature generally assures robustness as well as many desirable bulk and surface properties. Presently, polymeric nanoporous crystalline phases have been de- scribed for s-PS [10–18] and poly(2,6-dimethyl-1,4-phenylene oxide). [19] In particular, for s-PS, two nanoporous crystalline phases (d [10–13] and e [14–18] ) have been discovered, which can absorb several guest molecules producing clathrate [20–23] and intercalate [24–28] co-crystals. Films presenting s-PS/active-guest co-crystals have been proposed as advanced materials for optical, [29–34] mag- netic, [35,36] and ferroelectric [37,38] applications. Semicrystalline s-PS samples exhibiting the nanoporous d and e crystalline phases can rapidly and selectively absorb volatile organic compounds (mainly halogenated and aromatic) even when present at very low concentrations. [39–46] As a consequence, several applications in the field of chemical separations [39–46] and of molecular sensorics [47–51] for these inexpensive and reusable materials have been proposed. Recently, a solid-state sulfonation procedure of d form s-PS films, which allows an easy and uniform sulfonation of the phenyl rings of the amorphous phase, has been described. [52,53] In fact, this sulfonation procedure is able to preserve the thermodynamically unstable nanoporous d phase, essentially preserving its degree of crystallinity (generally in the range 30%–40%), also reaching high sulfonation degrees of the * Correspondence to: Vincenzo Venditto, Dipartimento di Chimica e Biologia, NANO_MATES Research Centre and INSTM Research Unit, Università degli Studi di Salerno, Via Ponte don Melillo, 84084, Fisciano, Italy. E-mail: vvenditto@unisa.it a A. Dembna Institute of Chemical Technology and Engineering, Poznan University of Tech- nology (Politechnika Poznańska), Pl. Sklodowskiej-Curie 2, 60-965 Poznan, Poland b V. Venditto, R. Califano, G. Guerra Dipartimento di Chimica e Biologia, NANO_MATES Research Centre and INSTM Research Unit, Università degli Studi di Salerno, Via Ponte don Melillo, 84084, Fisciano, Italy c A.R. Albunia Borealis Polyolefine GmbH, St.-Peter-Strabe 25, 4021 Linz, Austria Research Article Received: 03 February 2012, Revised: 20 April 2012, Accepted: 26 April 2012, Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/pat.3049 Polym. Adv. Technol. (2012) Copyright © 2012 John Wiley & Sons, Ltd.