Thermally reversible highly cross-linked polymeric materials based on furan/maleimide Diels-Alder adducts Placido Mineo, 1,2 Vincenzina Barbera, 3 Giovanni Romeo, 4 Fabrizia Ghezzo, 5 Emilio Scamporrino, 1 Fabiola Spitaleri, 1 Ugo Chiacchio 3 1 Dipartimento di Scienze Chimiche and I.N.S.T.M. UdR of Catania, Universit a di Catania, Viale A. Doria, 6, 95125 Catania, Italy 2 CNR-IPCF Istituto per i Processi Chimico Fisici, Viale Ferdinando Stagno D’Alcontres, 37, 98158. Messina, Italy 3 Dipartimento di Scienze del Farmaco, Universit a degli studi di Catania, Viale Andrea Doria 6, 95125 Catania, Italy 4 Dipartimento di Scienze del farmaco e prodotti per la salute, Viale Annunziata, Polo Universitario, Universit a degli studi di Messina, 98168 Messina, Italy 5 NEXAT Advanced Technology, Bright Way Tower, 7/F Mong Kok Road, Hong Kong Dedicated to Professor Antonino Corsaro on occasion of his seventieth birthday. Correspondence to: P. Mineo (E - mail: gmineo@unict.it) and U. Chiacchio (E - mail: uchiacch@unict.it) ABSTRACT: A novel thermally reversible cross-linked polymer has been synthesized by a Diels-Alder (DA) reaction between bis(4-mal- eimido-phenyl)fluorene (cBMI) and tetrakis-furan monomers (4F) under microwave (MW) irradiation. The ultimate aim of this work was the preparation of a thermosetting material recyclable by a simple thermal treatment. The use of the MW irradiation was necessary because under thermal conditions the DA polymerization could lead to materials only partially cross-linked for a not desired equilibrium between DA and retro-DA processes induced by the high temperature. The easy thermal degradation of this cross-linked material was ascertained by appropriate experiments. Moreover, to better study the involved reactions of formation and decomposition, a more simple model-compound was also synthesized. The reported data confirm the recyclability of the synthe- sized cross-linked polymer by simply heating with the possibility of a regeneration of the polymer network by a further MW irradia- tion. V C 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42314. KEYWORDS: crosslinking; polyimides; recycling; thermosets Received 3 January 2015; accepted 7 April 2015 DOI: 10.1002/app.42314 INTRODUCTION In these last years, the synthesis of self-healing materials, char- acterized by the capability of self-repairing or recovering after mechanically or thermally induced damages, has become a new emerging and fascinating field of research. 1–4 In this context, the Diels-Alder (DA) reaction constitutes a highly promising tool in order to introduce self-healing properties to polymeric systems. 5–8 In fact, one of the most interesting characteristic of this reaction is the thermal reversibility of some DA adducts by which it is possible to regenerate the starting materials. This intrinsic property suggests the synthesis of a new class of recyclable cross-linked polymers where the cross-link agent may be just the result of a DA multi-reaction. Often, the DA reaction between furans and maleimide deriva- tives has been used for the formation of thermally reversible bonds. This reversibility arises from the lower energy required to break the DA adducts with respect to any other covalent bond. Thus, after a DA reaction, the molecular structure can be subjected to dissociation upon heating, reforming the starting reagents (furan and maleimide derivatives) with the possibility, after cooling at room temperature, of the reconnection by appli- cation of a successive controlled heating. This phenomenon is frequently used to “repair” the cracks occurring into polymeric materials. The reaction has been extensively developed and the suitability of a DA-system for self-healing of a bulk material (as linear polymers, 9 net- works, 10,11 hydrogels, 12 and dendrimers 13 ), adequately demonstrated. The bis-maleimides based polymers are very interesting systems that possess many desirable properties such as a high tensile strength and an excellent chemical and corrosion resistance so V C 2015 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2015, DOI: 10.1002/APP.42314 42314 (1 of 9)