Imide-Containing Ladder Polyphenylsilsesquioxanes with High Thermal Stability and Thermoplastic Properties Ricardo Chavez, Emanuel Ionescu, Claudia Fasel, Ralf Riedel Technische Universit€ at Darmstadt, Institut f€ ur Materialwissenschaft, Petersenstrasse 32 D-64287 Darmstadt, Germany Correspondence to: E. Ionescu (E - mail: ionescu@materials.tu-darmstadt.de) ABSTRACT: This work reports for the first time the synthesis of ladder polyphenylsilsesquioxanes containing imide building blocks as parts of the main parallel chains. The ladder structure of the synthesized polymers was documented by means of small angle X-ray scattering (SAXS) measurements. The obtained ladder polymers exhibit stability with respect to decomposition up to temperatures as high as 460  C; additionally, they have melting points far below their decomposition temperatures, which make them interesting can- didate materials for thermoplastic processing. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40085. KEYWORDS: polyimides; thermoplastics; inorganic polymers; thermal properties Received 5 July 2013; accepted 20 October 2013 DOI: 10.1002/app.40085 INTRODUCTION Polysilsesquioxanes are silicon-containing polymers with the for- mula (RSiO 3/2 ) n where R can be hydrogen, alkyl, or aryl groups. 1–5 Currently, four classes of polysilsesquioxane struc- tures are known: amorphous, ladder, cube, and open cube. The ladder polysilsesquioxanes consist of two linear syndiotactic molecular chains that are linked periodically by siloxane units, SiAOASi. 5–7 Their structure has been studied using X-ray methods. These studies revealed that the distance between the parallel chains is about 12.5 A ˚ ; whereas the monomer length (repeating intrachain distance) is about 5 A ˚ . 7–10 These dimen- sions relate the appearance of two reflexes in their X-Ray dif- fractograms, at 2h values of 6.5  -8  and 18  -20  , respectively. 7–9 Depending on the side groups attached to the Si-atoms of the main parallel chains, the interchain distance can however vary. On the other hand, ladder polysilsesquioxanes have been also studied by 29 Si-NMR spectroscopy. These studies revealed that the siloxane unit present in the parallel main chains (T3 unit) is characterized by a broad signal at 280 ppm. 11 The ladder architecture of these materials leads to interesting properties. They have been shown to present high thermo- oxidative stability up to temperatures of 400–500  C, 6,8 high glass transition temperatures, 12 and high chemical stability. Thus, these polymeric compounds are currently used as coating materials 13 and insulators 12 for high temperature applications. Ladder polysilsesquioxanes with different side groups have been developed in order to introduce new properties. Thus, by add- ing perfluorated side groups, it is possible to obtain hydropho- bic coating materials. 14 Furthermore, it is also possible to have side groups with reactive functionalities, such as in aminopro- pylsiloxanes, which allow the ladder structures for further reactions. 15 Polyphenylsilsesquioxanes have been intensively studied among polysilsesquioxanes. These polymers were first described in 1960 by von Braun. 5,11 Typically, they are obtained by hydrolysis and further polycondensation of tri-functional monomers like Ph- SiX 3 , with X being chlorine, alkoxide or acetate groups. By using these methods, special care needs to be taken regarding the purity of the reagents and the synthesis conditions. Exam- ples of these synthesis conditions are a strict control of the reagents concentration, 5 removal of products or side products during the reaction, 5,8 and the use of base catalysts. 8 Otherwise, no ladder structures are obtained. 8 The need for performing the synthesis of polyphenylsilsesquioxanes under strict conditions implies high production costs, which hinder a broader use of polymers with ladder structure in large amounts. Thus, it is necessary to develop alternative synthesis methods that allow an easier and cost-effective production of polyphenylsilsesquioxanes with ladder structure. Polyphenylsilsesquioxanes became of technical interest as some of them show a melting point below their degradation tempera- ture, 12 thus allowing for their thermoplastic processing. The combination of high thermal stability and thermoplastic proper- ties is unusual to be present in the same material, making Additional Supporting Information may be found in the online version of this article. V C 2013 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2014, DOI: 10.1002/APP.40085 40085 (1 of 8)