Revue Roumaine de Chimie, 2008, 53(9), 803–811 Dedicated to the memory of Professor Cristofor I. Simionescu (1920–2007) NEW POLYIMIDES CONTAINING SILOXANE GROUPS IN THE MAIN CHAIN Maria BRUMĂ, a Ion SAVA, a* Mariana Dana DĂMĂCEANU, a Nataliya M. BELOMOINA b and Jenifer ROBISON c a Institute of Macromolecular Chemistry, Aleea Gr. Ghica Vodă 41A, Iaşi-700487, Roumania b Nesmeyanov Institute of Organoelement Compounds, ul. Vavilova 28, Moscow 119991, Russia c Tyco Electronics, 306 Constitution Drive, Menlo Park, CA 94025-1164, USA Received December 12, 2007 A series of polyimides and intermediate polyamidic acids has been synthesized by solution polycondensation reaction at high temperature of aromatic diamines containing flexible hexafluoroisopropylidene groups or cyano substituents with a dianhydride containing siloxane bridge. The solubility, thermal stability, film-forming ability and photoluminescence properties of these polymers have been evaluated and compared with those of related conventional polyimides which do not contain any flexible bridge nor substituents. INTRODUCTION ∗ Among the polymers widely studied for applications in advanced technique, aromatic polyimides have received considerable attention due to their outstanding thermal stability associated with good electrical and mechanical properties. 1-3 However, these polymers are usually difficult to process due to their rigid backbone structure which makes them insoluble and without glass transition in their fully imidized form. To improve the processing characteristics of polyimides, modification of their structure is often used by the introduction of flexible linkages in the macromolecular chain or various substituents on aromatic rings. 4-9 Our approach to improve the solubility and lower the glass transition temperature is the introduction of flexible bridges such as siloxane ( ─Si─O─Si ─) together with hexafluoroisopropylidene (6F) groups or cyano (CN) substituents in the macromolecular chain. Here we report the synthesis of new polyimides by polycondensation reaction of a dianhydride containing siloxane unit (I) with aromatic diamines containing 6F groups or CN substituents (II). The ∗ Corresponding author: isava@icmpp.ro properties of these polymers (III) such as solubility, thermal stability, film-forming and photoluminescence ability have been studied and compared with those of related polymers. RESULTS AND DISCUSSION The polyimides (III) and the corresponding intermediates (III') studied here are based on a dianhydride containing dimethyl-substituted siloxane group (I), namely 1,3-bis(4’-phthalic anhydride)tetramethyldisiloxane, and various aromatic diamines containing hexafluoroisopropylidene (6F) bridges or cyano (CN) substituents (II). The structures of these monomers are shown in Scheme 1. Polycondensation reaction of equimolar amounts of dianhydride I with diamines II, in NMP, yielded polyamidic acids III' at room temperature, and the corresponding polyimides III after heating at high temperature in solution under slow stream of nitrogen. The structures of polyimides and intermediate polyamic acids are shown in Scheme 2.