Furfuryl Alcohol Polymerization in H-Y Confined Spaces: Reaction Mechanism and Structure of Carbocationic Intermediates S. Bertarione, F. Bonino, F. Cesano, A. Damin, D. Scarano, and A. Zecchina* Department of Inorganic, Physical and Materials Chemistry, NIS Centre of Excellence, and Centre of Reference INSTM, UniVersity of Turin, Via P. Giuria 7, I-10125 Torino, Italy ReceiVed: May 22, 2007; In Final Form: NoVember 6, 2007 The acid-catalyzed polymerization and resinification, in the 300-673 K interval, of furfuryl alcohol adsorbed in the framework of a protonic Y zeolite is studied by means of FTIR, Raman, and UV-vis spectroscopies. The idea is that restricted spaces can impose a constraint to the growth of the oligomeric chains, therefore moderating the formation of conjugated sequences responsible for the color of the products and allowing their observation by means of spectroscopic techniques. The detailed study of the evolution of UV-vis, FTIR, and Raman spectra upon dosed amount, contact time, and temperature has allowed the spectroscopic features of some of the single species, either neutral and positively charged (carbocationic intermediates), to be singled out and assigned to understand the mechanism of initiation. The vibrational assignments have been confirmed by computer simulations on model compounds and compared with the results of the mechanistic description of the reaction mechanism made in the past (Choura, et al. Macromolecules 1996, 29, 3839- 3850). The spectroscopic methods have been applied in a large temperature range in order to follow also the formation of more complex products into the pores, associated with longer conjugated sequences, gradually filling the open spaces of the zeolite. For samples contacted with furfuryl alcohol at 673 K, this methodology gives information also on the incipient carbonization process, leading to the formation of a carbonaceous replica phase inside the internal porosity of the zeolite. 1. Introduction Carbonaceous materials derived from polymerization and resinification of furfuryl alcohol have found a useful range of applications in the production of corrosion-resistant materials, of low flammable and low smoke production composites, pastes and agglutinants, electrode materials, and adsorbent materials for methane and hydrogen storage. 1-12 Acid-catalyzed oligomerization and resinification have been studied intensively in the past, and in general terms, the features of the process are understood. However, many aspects of the process, including the initiation mechanism, are still unknown. For sake of simplicity, we can consider the processes of oligomerization and resinification as separate, the first one occurring at low temperature and the second one becoming predominant at higher values. We shall see in the following that this assumption is not completely valid because there is no clear-cut difference between the two processes and that partial resinification occurs already during oligomerization. Coming now to the acid-catalyzed oligomerization, Dunlop and Peters, 1 have hypothesized two main mechanisms for the initiation of the process (see Schemes 1 and 2): (1) The oligomerization occurs via a condensation reaction between the OH of the methylol group of one furan ring and the 5-position of another furan ring, leading to water elimination and formation of a methylene linkage (Scheme 1). This process can continue and lead to the formation of long oligomeric chains. (2) The condensation reaction occurs between the OH of the methylol group of one furan ring and the methylol group of another furan ring to form a dimethylene ether linkage (Scheme 2). This mechanism can explain the formation of dimeric species but not the polymeric ones. Of course, if these two mechanisms are simultaneously operating, long linear chains containing both types of bridges can be present in the final product. In fact, the oligomers formed during the process following Scheme 1 can, in principle, react * Corresponding author. Phone: +39 011 6707860. Fax: +39 011 6707855. E-mail: adriano.zecchina@unito.it. SCHEME 1: Condensation Reaction between the OH of the Methylol Group of One Furan Ring and the 5-Position of Another Furan Ring to Form a Methylene Linkage SCHEME 2: Condensation Reaction between the OH of the Methylol Group of One Furan Ring and the Methylol Group of Another Furan Ring to Form a Dimethylene Ether Linkage 2580 J. Phys. Chem. B 2008, 112, 2580-2589 10.1021/jp073958q CCC: $40.75 © 2008 American Chemical Society Published on Web 02/12/2008