Thermochimica Acta 494 (2009) 45–53 Contents lists available at ScienceDirect Thermochimica Acta journal homepage: www.elsevier.com/locate/tca Thermolysis of new hybrid silsesquioxane–carbosilane materials Anna Kowalewska a,∗ , Witold Fortuniak a , Krystyna Rózga-Wijas a , Bartosz Handke b a Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Lód´ z, Poland b AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Al. Mickiewicza 30, 30-059 Kraków, Poland article info Article history: Received 15 January 2009 Received in revised form 17 April 2009 Accepted 21 April 2009 Available online 3 May 2009 Keywords: Thermolysis Silsesquioxane Carbosilane Tris(trimethylsilyl)methane abstract Thermal decomposition of new silsesquioxane materials [(Me 3 Si) 3 CSiMe 2 CH 2 CH 2 SiO 3/2 ] n (PT Si SS), substi- tuted with sterically hindered carbosilane groups, was studied in an inert atmosphere (N 2 ) and air. It was found that a specific degradation of carbosilane moieties occurs at high temperatures. A ceramic residue was obtained > 900 K both in nitrogen (Si x O y C z ) and air (Si x O y ). Thermal rearrangements in the structure of polyhedral and ladder-like PT Si SS were studied, and related to those observed for a polymethylsilsesquiox- ane resin (PMSS) of regular ladder-like architecture. Thermally induced transformations were evaluated by TGA(DTA)-MS, FTIR, NMR, XRD and SEM. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Polyhedral silsesquioxane units introduced into polymeric nanocomposite materials can improve their thermal, mechani- cal and dielectric properties [1–10]. The investigation of their decomposition at high temperatures can provide an insight into the system stability and explain the mechanism of conversion into a ceramic material [11]. Thermolysis of various octahedral [12–17] and polymeric [18–30] silsesquioxanes has been thus stud- ied. Completely condensed octahedral POSS {T 8 R ,R c-C 6 H 11 [12], C n H 2n+1 (n = 2–10) [13], Me, Vi, i-Bu, i-Oct [14], CH 2 CH 2 OCH 2 CH 2 Cl [15], OSiMe 2 H [16], OSiMe 2 CH 2 CH 2 Ph [17]} were found to sub- lime on heating in an inert atmosphere. It was shown that on increasing the length of alkyl chain from C 2 to C 10 in octahedral POSS the weight loss onset (due to volatilisation and decom- position) shifted to higher temperatures [13]. Octahedral POSS with simple organic substituents that do not sublime at ele- vated temperatures in N 2 can be found among these tending to form chars of aromatic structure on decomposition. T 8 Ph is thermally stable up to 620 K in N 2 and leaves 70% of ceramic residue > 1000 K [14]. Acetoxyphenyl and hydroxyphenyl substi- tuted POSS, capable of hydrogen bonding, gave respectively 60% and 70% char yields at 1100K [17]. Very recently we have reported preparation of a new type of hybrid silsesquioxane materials – [(Me 3 Si) 3 CSiMe 2 CH 2 CH 2 SiO 3/2 ] n (PT Si SS) – bearing a sterically hindered tris(trimethylsilyl)methyl (T Si )-type ligands [31] .They ∗ Corresponding author. Tel.: +48 4268 03203; fax: +48 4268 47126. E-mail address: anko@cbmm.lodz.pl (A. Kowalewska). are built of octahedral or ladder-like silsesquioxane framework surrounded by nonpolar carbosilane ligands. Contrary to com- mon octahedral T 8 molecules, [(Me 3 Si) 3 CSiMe 2 CH 2 CH 2 SiO 3/2 ] 8 (PT Si SS-I, Scheme 1) do not sublime on heating in nitrogen atmo- sphere. Comparative thermogravimetric analysis [32] of octahedral silsesquioxanes functionalized with typical organic groups (Me, Vi, Ph) and PT Si SS-I points out to the unique properties of the latter. Bulky T Si groups were already shown to provide an excep- tional steric protection to polymeric systems, resulting in an effective separation of polymeric chains and a substantial decrease in their mobility [33–38]. Consequently, an improved material performance, glass transition temperature increase and ther- mal resistance enhancement are observed. Octahedral, crystalline (PT Si SS-I) and ladder-like, polymeric (PT Si SS-II) silsesquioxanes bearing T Si groups were thus examined for the structural changes occurring during their thermolysis. It is known that the steric strain within T Si ligand is decreased by a specific arrangement of Me 3 Si-substituents about the cen- tral carbon atom [39–41]. Due to the significant difference in the length of Si C bonds within T Si moiety (inner Si C q and outer Si CH 3 ), breaking of the former was found to be more feasible during UV-laser induced decomposition of siloxanes with side tris(trimethylsilyl)hexyl groups [35]. The difference in the bond length between inner Si C q and outer Si CH 3 in T Si moiety is also the cause of a particular thermal transition and heat capac- ity change in PT Si SS. Combined DSC and variable temperature NMR ( 29 Si and 13 C) methods indicated an increase in mobility of Me 3 Si groups above this temperature [31]. The finding was thought to be of importance for the mechanism of thermolysis of PT Si SS. Accord- ingly, it was expected that C SiMe 3 bonds would break easily at 0040-6031/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2009.04.016