ORIGINAL PAPER Polymer Chain Relaxation Mechanisms in Siloxane-Carbosilane Systems Anna Kowalewska & Sławomir Kaźmierski & Bogumiła Delczyk-Olejniczak Received: 6 December 2010 / Accepted: 14 February 2011 / Published online: 5 March 2011 # Springer Science+Business Media B.V. 2011 Abstract The effect of sterically hindered carbosilane moieties, situated as end groups in telechelic oligodimethyl- siloxanes, was investigated with respect to the mobility of silicon atoms in the main chain. The relaxation phenomena in such crowded systems were studied by DSC and NMR methods. Spin–lattice relaxation times T 1 ( 29 Si NMR) of silicon atoms in the oligomer chain were estimated and related to the distance between a given siloxane unit and the carbosilane moiety. It was found that the mobility of terminal siloxane units has been substantially affected. However, in the long range, the effect does not to seem to outweigh the intrinsic flexibility of the siloxane bonds. Keywords Siloxane . Carbosilane . Tris(trimethylsilyl) methane . Segmental mobility . Relaxation 1 Introduction Carbosilane derivatives of the tris(trimethylsilyl)methyl (Tsi) moiety, due to their exceptional steric hindrance, have been extensively used both in organometallic [1, 2] and polymer chemistry [3–12]. Tsi-modified polymeric materials exhibit quite unique properties. For example, a specific change in mobility of Me 3 Si groups results in a distinct γ-type relaxation transition in ladder Tsi-silsesquioxanes, discernible by the differential calorimetry method [8]. The properties, that can be brought in by Tsi functions are of special interest regarding siloxane polymers. Polysiloxanes have low surface tension, good elasticity at low temperatures and, due to outstanding flexibility of Si-O-Si bonds, can provide good permeability (but low selectivity of diffusion) for fluids [13]. Their molecular conformation can change depending on the kind of side groups [14], resulting in a modification of the material structure and properties. Bringing sterically de- manding Tsi moieties into polysiloxane materials should be of great importance for their properties. The relationship between the mobility of a polymer chain and the type of Tsi carbosilane moiety, and its distribution along the main backbone, was recently studied for an homologous series of poly(dimethyl-methyl)siloxanes [5]. It was found that Tsi- type side groups can restrict the movement of polymer segments and in consequence lead to a tremendous increase of the glass transition temperature and thermal stability of all the studied siloxane materials. However, the effect of the adjacent Tsi in side positions to Si atoms in polymer chains could not be quantitatively estimated. Telechelic dimethylsi- loxane oligomers, α,ω-functionalized with Tsi groups, were thus chosen as a simple model system for the study into the mobility divergence of monomeric siloxane units, depending on their position with respect to carbosilane moieties. Measurement of spin–lattice relaxation times T 1 ( 29 Si NMR) of respective silicon atoms was chosen as a tool for the assessment. The results were correlated with the observed change of phase transitions of studied oligomers and their thermal stability. 2 Results and Discussion 2.1 Preparation and Properties of Telechelic Oligosiloxanes with Bulky Carbosilane End Groups 6-[Tris(trimethylsilyl)]-hex-1-ene and tris(trimethylsilyl) (vinyldimethylsilyl)methane were used for preparation of oligomeric siloxane materials, by their hydrosilylation with A. Kowalewska (*) : S. Kaźmierski : B. Delczyk-Olejniczak Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90–363 Łódź, Poland e-mail: anko@cbmm.lodz.pl Silicon (2011) 3:37–44 DOI 10.1007/s12633-011-9074-y