Copoly(peryleneimide)s Containing 1,3,4-Oxadiazole Rings: Synthesis and Properties RADU-DAN RUSU, MARIANA-DANA DAMACEANU, LUMINITA MARIN, MARIA BRUMA ‘‘Petru Poni’’ Institute of Macromolecular Chemistry, Aleea Grigore Ghica Voda 41A, Iasi 700487, Romania Received 20 May 2010; accepted 29 June 2010 DOI: 10.1002/pola.24209 Published online in Online Library (wileyonlinelibrary.com). ABSTRACT: New copolyimides containing perylenediimide, oxa- diazole and hexafluoroisopropylidene moieties were prepared by one-step polycondensation reaction in solution at high tem- perature of aromatic diamines containing preformed oxadia- zole ring with a mixture of a dianhydride having a perylene ring and another dianhydride with hexafluoroisopropylidene unit. The thermal stability and glass transition temperatures of these copolyimides were measured and compared with those of related polyimides. The solid polymers were also studied by polarized light microscopy and X-ray diffraction which revealed a semicrystalline state consisting of face-to-face arranged col- umns of perylenediimide units. The film-forming ability and properties of the resulting thin films were investigated by using atom force microscopy and scanning electron micros- copy which showed that the films were organized into self- assembled rod-like structures. The UV-Vis and photolumines- cence properties in solution and in solid state were also investigated. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4230–4242, 2010 KEYWORDS: crystallinity; high temperature materials; photo- optical properties; polyimides; thin films INTRODUCTION Polymeric electroluminescent devices (ELDs) have received much attention in recent years because of their color tunability, low operating voltages, ease of fabrication, and especially potential application for self-emitting full color flat panel displays. 1 One of the major issues for real application of ELDs is their degradation under continuous operation. To fabricate ELDs with high stability, much research has been performed to improve the stability of organic materials and the interface between the metal electrode and the organic thin film. 2 Polyimides have various outstanding characteristics such as good adhesion to metal, high thermal stability, low thermal expansion, excellent film-forming properties, and especially a high glass transition temperature (T g ), of above 200  C, which make them potentially useful as stable materials for ELDs. 3 Among the polyimides, those containing perylene units appear to possess one of the highest thermal stability because of the condensed aromatic perylene ring. Perylene- diimides represent one of the most important n-type semi- conductor organic materials, providing prospects for applica- tions in organic photovoltaic devices, electrophotography, artificial light-harvesting complexes, solar cells, field-effect transistors and light-emitting diodes. 4–7 Perylenediimides are inexpensive and robust materials (the parent anhydride is a common automobile paint pigment), and they are highly fluorescent and exhibit singlet energy transfer over unusu- ally long distances. 8 However, research using polyimides containing perylene in optoelectronic fields can rarely be found so far, 9,10 which may be due to the poor solubility of perylenediimide polymers in common organic solvents. Therefore, the design and preparation of soluble poly(perylene- imide)s, to give satisfactory processability of products with- out a perceptible loss of favorable properties, is an important and urgent problem in the chemistry of heat resistant polymers. 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, 11,12 a combined approach was under- taken through the synthesis of copoly(peryleneimide)s con- taining oxadiazole rings and flexible groups such as ether or hexafluoroisopropylidene. The use of 1,3,4-oxadiazole ring in the construction of co- polyimides is based on the already known high performance properties of aromatic polyoxadiazoles, such as high thermal re- sistance, good hydrolytic stability, low dielectric constant, tough mechanical behavior, and other special properties determined by the electronic structure of this particular heterocycle. 13,14 Poly(1,3,4-oxadiazole)s are of great interest for ELDs due to electron-withdrawing character of the 1,3,4-oxadiazole ring that can facilitate the injection and transport of electrons. 15 On the other hand, it was shown that the inclusion of hexa- fluoroisopropylidene (6F) units into polymers can increase the solubility, thermal stability, flame retardancy, oxidation resistance, transparency and environmental stability. 16 Correspondence to: R.-D. Rusu (E-mail: radu.rusu@icmpp.ro) Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 4230–4242 (2010) V C 2010 Wiley Periodicals, Inc. 4230 WILEYONLINELIBRARY.COM/JOURNAL/JPOLA