Received: 10 June 2009, Accepted: 26 June 2009, Published online in Wiley Online Library: 2 August 2009 New thermally stable and organosoluble heterocyclic poly(naphthaleneimide)s y Mariana-Dana Damaceanu a * , Radu-Dan Rusu a , Maria Bruma a and Alexander L. Rusanov b As majority of polyheteroarylenes based on bis(naphthalic anhydrides), are difficult to process due to their infusiblity and insolubility in common organic solvents and solubility only in strong acids, this study is concerned with the synthesis and properties of new, easily processable polyimides and copolyimides containing naphthalene and oxadiazole rings. These polymers have been synthesized and their properties have been compared with regard to the influence of oxadiazole and naphthalene units on their physical properties. The polyimides were prepared by polycondensation reaction in solution of the aromatic diamines containing preformed oxadiazole ring with two dianhydrides having naphthalene units, at high temperature. Also, copolyimides were prepared by using a mixture of each naphthalene-containing dianhydride, with hexafluoroisopropylidene-dianhydride in the polycondensation reaction with the same diamino-oxadiazoles. Most of the resulting polyimides and copolyimides were soluble in polar amidic solvents and in less polar solvents, and their solutions gave flexible films when spread onto glass plates. The thermal stability and glass transition temperature of these polyimides and copolyimides were measured and compared. The quality and the roughness of the spin-coated films of these polymers were investigated by atomic force microscopy. The photoluminescence properties of the polymers in solution were studied to determine the color of emission. The UV absorption was also studied to determine the Stokes shift, and hence the possible reabsorption effects. The properties of the present polyimides make them attractive for applications in advanced optoelectronics and other related fields. Copyright ß 2009 John Wiley & Sons, Ltd. Keywords: polynaphthaleneimides; solubility; high thermostability; thin flexible films; blue-light emission INTRODUCTION Aromatic polyimides are well accepted as high performance polymeric materials for their excellent heat and chemical resistances, favorable electrical insulating properties, and tough mechanical characteristics. [1,2] Polyimides containing a six member imide ring, possessing naphthalimide structure, have received little attention, primarily due to the inability of obtaining soluble precursors for fabrication. Preliminary investigations have shown that polynaphthylimides, which are formed when bis(naphthalic anhydrides) are employed as monomers, display superior chemical, thermal, and fire resistance, compared with the analogous systems derived from bis(phthalic anhydrides). Moreover, polyimides based on naphthalene-1,4,5,8-tetracar- boxylic acid dianhydride (DNTA) are of considerable interest due to easy accessibility of the starting monomers. DNTA is a widely available dianhydride, showing the highest electrophilic reactiv- ity among naphthalene tetracarboxylic dianhydrides. As a consequence, in view of design of materials possessing improved properties, polymers based on bis(naphthalic anhydrides) seem to be more perspective than the analogous polymers derived from bis(phthalic anhydrides). [3–5] But, it should be noted that the majority of polyheteroarylenes, based on bis(naphthalic anhy- drides), are difficult to process, being infusible and insoluble in common organic solvents and soluble only in strong acids. In fact, unless carefully designed, polyimides are often insoluble in their fully imidized form. Thus, their use in versatile applications is often limited. Therefore, the design and preparation of soluble polynaphthylimides, to give satisfactory processability of pro- ducts without a perceptible loss of favorable properties, are important and urgent problems in the chemistry of heat resistant polymers. Much research is being carried out in order to find new soluble polyimides, which can be processed in their fully imidized form. [6,7] Being known that the introduction of flexible groups or/ and certain supplemental heterocycles into the backbone of fully aromatic polymers can lead to soluble products, a combined approach was undertaken through the synthesis of five- membered polyimides containing oxadiazole rings, which introduce a deviation from the linearity of the chain, and flexible groups such as hexafluoroisopropylidene (6F) or carbonyl. [8,9] The use of 1,3,4-oxadiazole ring in the construction of copolyimides is based on the already known high performance (wileyonlinelibrary.com) DOI: 10.1002/pat.1519 Research Article * Correspondence to: M.-D. Damaceanu, ‘‘Petru Poni’’ Institute of Macromol- ecular Chemistry, Aleea Grigore Ghica Voda 41A, Iasi-700487, Romania. E-mail: damaceanu@icmpp.ro a M.-D. Damaceanu, R.-D. Rusu, M. Bruma ‘‘Petru Poni’’ Institute of Macromolecular Chemistry, Aleea Grigore Ghica Voda 41A, Iasi-700487, Romania b A. L. Rusanov Nesmeyanov Institute of Organoelement Compounds, ul. Vavilova 28, Moscow 119991, Russia y The financial support provided through Romanian Program PNCD-2, contract no. 11008/2007 is warmly acknowledged. Polym. Adv. Technol. 2011, 22 420–429 Copyright ß 2009 John Wiley & Sons, Ltd. 420