Synthesis and study of new silicon-containing polyoxadiazoles E. Hamciuc a , M. Bruma a , T. Ko ¨pnick b , Y. Kaminorz c , B. Schulz d, * a Institute of Macromolecular Chemistry, Aleea Ghica Voda 41 A, Iasi 6600, Romania b Institute of Thin Film Technology and Microsensorics, Kantstr. 55, Teltow 14513, Germany c University of Potsdam, Institute of Physics, Physics of Condensed Matter, Postfach 601553, Potsdam 14415, Germany d University of Potsdam, Research Centre Thin Organic and Biochemical Films, Kantstrasse 55, Teltow 14513, Germany Received 5 December 1999; received in revised form 4 June 2000; accepted 25 June 2000 Abstract A series of new poly-1,3,4-oxadiazoles has been synthesized by polycondensation reaction of hydrazine sulfate with a mixture of a dicarboxylic acid containing unsaturated bonds and a dicarboxylic acid containing silicon, by using methanesulfonic acid/phosphorus pentoxide as a reaction medium. These polymers were highly thermostable but they were only soluble in strong inorganic acids such as sulfuric or methanesulfonic ones. An alternative way was followed by using the corresponding dihydrazides containing unsaturated bonds and the corresponding diacid chloride containing silicon that reacted in N-methylpyrrolidinone (NMP) to give soluble silicon-containing unsaturated polyhydrazides, which were cyclodehydrated either by thermal or chemical treatment to give the corresponding polyoxadiazoles. Very thin coatings of polyhydrazides and polyoxadiazoles were deposited onto silicon wafers and they showed a very smooth surface, free of pinholes, when studied by atomic force microscopy (AFM). Some polyoxadiazole films showed strong blue photoluminescence.  2000 Elsevier Science Ltd. All rights reserved. Keywords: Poly(1,3,4-oxadiazole)s; Diphenylsilane groups; AFM investigations 1. Introduction Poly(1,3,4-oxadiazole)s have been the focus of consider- able attention with regard to the production of high-perfor- mance materials, particularly owing to their high thermal stability and tough mechanical properties, along with a fruit- ful combination of optical and electronic properties deter- mined by the specific structure of 1,3,4-oxadiazole ring [1,2]. Like other conjugated aromatic or heteroaromatic polymers, such as poly(p-phenylene) [3,4], poly(p-pheny- lene-vinylene) [5,6] or polythiophene [7,8], poly(arylene- 1,3,4-oxadiazole)s [9–11] and poly(arylene-vinylene- 1,3,4-oxadiazole)s [12] have attracted much interest because they can easily undergo chemical and electroche- mical redox reactions and the resulting conducting materials may be used in electrochemical sensors or electrolumines- cent devices, for data display, optical data processing and other. However, poly(arylene-1,3,4-oxadiazole)s and poly- (arylene-vinylene-1,3,4-oxadiazole)s are rigid, rod-like molecules and are insoluble in organic solvents and do not exhibit a glass transition (T g ) which makes their processing quite difficult. Many approaches have been undertaken to improve the solubility and lower the T g , hence to make such polymers processable, for example by introducing flexible side groups on the aromatic rings [13] or bulky moieties such as “cardo” groups [14] in the main chain, provided that the main chain conjugation is not disturbed. Another way to improving solubility and lowering the T g of aromatic polymers is the introduction of diphenylsilane units in the main chain [15]. Moreover, electrochemical studies have shown that when incorporated between two para-phenylene rings in the main chain the silicon atom gives a s – p conju- gation and supports the transport of electrons [16]. There- fore, we considered that by introducing diphenylsilane units together with some unsaturated bonds in the main chain of aromatic polyoxadiazoles a better balance of useful proper- ties and processing ability, particularly better film-forming capability would be reached. We report here the synthesis of new polyoxadiazoles either by direct reaction of hydrazine sulfate with a mixture of a dicarboxylic acid containing unsaturated bonds and a dicarboxylic acid having diphenylsilane groups, or by the reaction of the corresponding dihydra- zides containing unsaturated bonds with the correspond- ing diacid chloride containing silicon via precursor polyhydrazides which were then thermally or chemically cyclodehydrated. The properties of these polymers, such as solubility, thermal stability, glass transition, as well Polymer 42 (2001) 1809–1815 0032-3861/01/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S0032-3861(00)00457-2 www.elsevier.nl/locate/polymer * Corresponding author. Tel.: +49-3328-46-508; fax: +49-3328-46-510.