Novel soluble thermally stable silane-containing aromatic polyimides with reduced dielectric constant Samal Babanzadeh a , Ali Reza Mahjoub a, ** , Shahram Mehdipour-Ataei b, * a Tarbiat Modares University, Department of Chemistry, Tehran 141554838, Iran b Iran Polymer and Petrochemical Institute, P.O. Box 14965/115, Tehran, Iran article info Article history: Received 3 May 2010 Received in revised form 26 July 2010 Accepted 1 August 2010 Available online 10 August 2010 Keywords: Polyimide Thermal properties Silane Dielectric constant abstract Bis(p-aminophenoxy)diphenylsilane (BPS), bis(m-aminophenoxy)diphenylsilane (BMS) and bis(5-amino- 1-naphthoxy)diphenylsilane (BAS) as three silane-diamines were prepared by the reactions of 4-ami- nophenol, 3-aminophenol, and 5-amino-1-naphthol respectively, with dichlorodiphenylsilane in the presence of triethylamine. The related silane-containing polyimides were prepared by two-step poly- condensation reactions of these diamines with three different aromatic dianhydrides. All the polymers were characterized and their physical and thermal properties were studied. The polymers showed high thermal stability while their solubility was greatly increased in polar aprotic solvents. Wide angle X-ray diffraction showed that all the polyimides were almost amorphous. Also their dielectric constants were decreased due to the incorporation of softening and low-polarizing siloxane units into the polymer backbone. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Recently rapid developments in the area of thermo-resistant engineering plastics have been observed. Polyimide (PI) materials have attracted attentions due to their high thermal stability, solvent resistance, excellent insulating integrity, good mechanical strength, excellent dimensional stability, low coefficient of friction, high dielectric strength, low dielectric constant, low outgassing, and resistance to creep and wear [1e4]. Due to their unique and specific properties they use as adhesives, films, composite matrices, coatings, membranes, and so on in severe environments. Application of these aromatic polymers is growing steadily because of increased performance characteristics deman- ded of polyimides in various fields including the aerospace, auto- mobile, and microelectronic industries. However, they are generally insoluble and infusible. Almost all of the prepared polyimides for the purpose of high temperature properties have more or less difficulties in processing and fabricating owing to their generally low solubility and high melting or glass transition temperatures. Most conventional processing techniques involve the fabrica- tion of polyamic acid precursors followed by thermal or chemical imidization in order to prepare related polyimides. Problems can arise because polyamic acids are thermally and hydrolytically unstable. The evolved water from imidization can also form voids in bulk materials. Therefore, a great deal of efforts has been expended to improve the processing characteristics of these relatively intractable polyimides [5,6]. Numerous methods to obtain polyimides with chemically modified chain structures have been introduced for balancing of the thermal stability and the processability. The most important methods include incorporation of hinge atoms, kink units, or flex- ible spacer units either into the dianhydride or diamine fragment or both. The introduction of bulky pendant (cardo) groups into the backbone of polymers is another approach to improve solubility and thereby processability of the polyimides [7e15]. Extensive studies on the structureeproperty relationship of pol- yimides have indicated that the problems in processing of conven- tional aromatic polyimides are resulted from the inherent molecular features of aromatic polyimides such as the molecular chain stiffness, high polarity, and high intermolecular association force. Thus, the main structural modifications to attain processable polyimides have been carried out by introducing flexible spacers and also bulky substitutes such as pendent aryl rings into their backbone. In this study, a novel group of silane-diamines containing bulky aromatic groups were synthesized and characterized. Subsequently, the related polyimides were prepared from these diamines and different aromatic dianhydrides. Incorporation of bulky groups and * Corresponding author. Tel.: þ98 21 44580000; fax: þ98 21 44580023. ** Corresponding author. Tel.: þ98 21 82883442; fax: þ98 21 88009730. E-mail addresses: mahjouba@modares.ac.ir (A.R. Mahjoub), s.mehdipour@ippi. ac.ir (S. Mehdipour-Ataei). Contents lists available at ScienceDirect Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab 0141-3910/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymdegradstab.2010.08.001 Polymer Degradation and Stability 95 (2010) 2492e2498