Reactive and Functional Silicones for Special Applications
With a history of almost 100 years, silicones -polymeric or oligomeric siloxanes- are well known as reliable materials with a wide range of applications, from home to the aerospace sector. The constant interest for these polymers is explained by their uni
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Reactive and Functional Silicones for Special Applications Carmen Racles, Mihaela Dascalu, Adrian Bele, and Maria Cazacu
Abstract With a history of almost 100 years, silicones -polymeric or oligomeric siloxanes- are well known as reliable materials with a wide range of applications, from home to the aerospace sector. The constant interest for these polymers is explained by their unique combination of properties, including chemical and physiological inertness, extreme resistance to ozone and corona discharge, film forming capacity, good thermal-oxidative and ultraviolet (UV) stability, high flexibility of the macromolecular chain, low dielectric constant, surface energy and transition temperatures, permeability to various gases, stability towards atomic oxygen and oxygen plasma, and UV-visible radiation transparency. The chemical modification of silicones is an active research area, since the attachment of several organic functional groups to the silicon atom imparts specific properties and triggers new applications. Functional siloxanes represent a bridge between siloxane and organic chemistry and combine valuable properties of silicones with reactivity and specific functions of organic moieties. In this chapter, the recent research progress in the field of functional organic siloxanes and their materials are reviewed, focusing on their applications in science and technology. Keywords Functional siloxanes · Polysiloxanes · Silicone materials
11.1 Introduction Silicones, also known as polysiloxanes, are synthetic polymers consisting of an inorganic backbone chain made of alternating silicon and oxygen atoms, with organic side groups attached to each silicon atom, with general formula [–OSiR2–]n. This class of materials has a unique combination of properties (Kuo 1999), derived from the particularities of the siloxane bond. Its length (1.64 Å) indicates a partial double bond character and a lower basicity than that of ethers, while the very low C. Racles (*) · M. Dascalu · A. Bele · M. Cazacu Department of Inorganic Polymers, “Petru Poni” Institute of Macromolecular Chemistry, Iasi, Romania e-mail: [email protected] © Springer Nature Switzerland AG 2020 T. J. Gutiérrez (ed.), Reactive and Functional Polymers Volume One, https://doi.org/10.1007/978-3-030-43403-8_11
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energy barriers for the rotation around Si-O axis (2.5 kJ mol-1 in dimethylsiloxane) and the linearization of Si-O-Si angle (1.3 kJ mol-1) explain the unusual flexibility of the polysiloxane chain. The Si-O-Si angle (140–180°) is much wider than the tetrahedral angle, while the siloxane bond is one of the most stable bonds formed by silicon, being estimated in the range 422–494 kJ mol-1 (Voronkov et al. 1978; Chojnowski and Cypryk 2000). The extreme flexibility of the siloxane backbone is reflected in the low glass transition temperature (Tg) value which is around -125 °C in poly(dimethylsiloxane) (PDMS), the best-known representative of this class of materials. By modifying the organic groups attached to the silicon at
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