Revue Roumaine de Chimie, 2007, 52(1–2), 117–125 Dedicated to Professor Ionel Haiduc on the occasion of his 70th anniversary SILOXANE-AZOAROMATIC POLYESTERS AS POTENTIAL COMPLEX DYE SYSTEMS Carmen RACLES,* Anton AIRINEI, Aurelia IOANID, Cristian GRIGORAS and Maria CAZACU “Petru Poni” Institute of Macromolecular Chemistry, Aleea Gr. Ghica Voda 41A, Iasi, 700487, Roumania E-mail: raclesc@icmpp.ro Received January 23, 2007 New polyesters with siloxane-organic main chain and azobenzene side groups were used in physical mixtures with different polymers (aromatic polysulfones, polydimethylsiloxane, hydroxypropylcellulose), in order to study the intermolecular interactions. By electronic absorption spectroscopy, DSC, optical and electronic microscopy, we investigated the compatibility within the blends, as a function of siloxane length and matrix polymer’s chemical structure. INTRODUCTION New siloxane polyesters with azoaromatic side groups have been synthesized by direct polycondensation, at room temperature, starting from Disperse Red 19 and different siloxane- organic diacids, using dicyclohexylcarbodiimide (DCC) as an activating agent and 4-(N,N- dimethylamino)pyridinium-p-toluenesulfonate (DPTS) as catalyst. 1 By their complexity, these polymers can be regarded as multifunctional materials. The presence of the azoaromatic chromophore induces a specific behavior as dye polymers, confering photosensitivity and high dye capacity. On the other hand, the azoaromatic groups act as mesogenic moieties. The variations in the siloxane-organic structures of the main chain tailor the thermal and thermotropic LC properties of the polyesters. The presence of the mesophases, their type and range and the LC transition temperatures depend on the chemical structure of the main chain. The siloxane moieties are responsible for the biphasic morphology and modified surface properties. The possibility of nanostructured morphology, as a result of thermodynamic incompatibility between the siloxane-based main chain and the lateral aromatic groups, is interesting for possible optical aplications. The polymers’ surface properties may be useful in applications such as coatings or dyes. Polysiloxanes are known to impart hydrophobicity or water repellency. The surface enrichment in Si and the formation of a silicon surface layer was widely reported for siloxane-containing block copolymers and blends. 2-7 The explanation of such behavior is the preferential orientation of the siloxane fragments towards the surface, due to their very low surface tension. This aspect, evidenced in the case of the azoaromatic siloxane polyesters, 1 may be exploited in the perspective of complex materials hydrophobization. In this paper, we present some results of our attempt to study the behaviour of siloxane- azoaromatic polyesters as complex dye systems. The siloxane moieties improve the water repellency, while the polar functional groups may lead to intermolecular interactions (such as H- bondings, arene-arene or dipol-dipol forces) with other polymers. Physical mixtures with polymers having various structures (aromatic polysulfones, polydimethylsiloxane, hydroxypropylcellulose) have been obtained. They have been investigated for photochemical behavior and thermal properties. By UV-VIS spectroscopy, the level of intermolecular interactions has been estimated, following the variation of the absorption maxima of azobenzene chromophore. The modifications of the polymers’ glass transition temperatures, in the presence of different amounts of siloxane-azoaromatic polyesters have been investigated by DSC. The compatibility